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The Book of the Sea

The realms of the Baltic Sea

BALTIC ENVIRONMENTAL FORUM

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T h e r e a l m s o f t h e Ba lt i c S e a


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THE BOOK OF THE SEA

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T h e r e a l m s o f t h e Ba lt i c S e a


The Book of the Sea. The realms of the Baltic Sea

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THE BOOK OF THE SEA

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T h e r e a l m s o f t h e Ba lt i c S e a


The Book of the Sea

The realms of the Baltic Sea

Gulf of Bothnia

Åland Islands

Oslo

Helsinki Gulf of Finland

A compilation by Žymantas Morkvėnas and Darius Daunys

Stockholm Tallinn Hiiumaa

Saaremaa

Skagerrak

Gulf of Riga Gotland Kattegat

Riga

Öland

Baltic Sea

Copenhagen

Klaipėda Bornholm

Bay of Gdańsk

Rügen

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Baltic Environmental Forum 2015

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T h e r e a l m s o f t h e Ba lt i c S e a


Table of Contents

Published in the framework of the

Project partners:

7 Preface

Authors of compilation Žymantas Morkvėnas and Darius Daunys

project „Inventory of marine species

Marine Science and Technology

and habitats for development of

Centre (MarsTec) at Klaipėda

Natura 2000 network in the offshore

University,

waters of Lithuania (DENOFLIT)“

Institute of Ecology of the Nature

(LIFE09 NAT/LT/000234),

Research Centre,

financed by the European Union

The Fisheries Service under the

LIFE+ programme, the Republic

Ministry of Agriculture of the

Illustrations by Saulius Karalius

of Lithuania and project partners.

Republic of Lithuania,

Photographs by Žymantas Morkvėnas and Erlandas Paplauskis

Project implementation period:

State Service for Protected Areas

Maps compilation by Ingrida Bagdanavičiūtė

2010–2015.

under the Ministry of Environment,

Design by Gedas Čiuželis

Baltic Environmental Forum Lithuania,

Edited by Rita Maksimavičienė

Linas Ložys, Jūratė Lesutienė, Albertas Bitinas, Martynas Bučas,

9 Ecosystem of the Baltic Sea 11 Geological development

Loreta Kelpšaitė-Rimkienė, Dalia Čebatariūnaitė, Nerijus Žitkevičius,

of the Baltic Sea

Greta Gyraitė, Arūnas Grušas, Erlandas Paplauskis, Radvilė Jankevičienė,

14 18 21 24 26 28

The coasts of the Baltic Sea

Texts provided by Darius Daunys, Žymantas Morkvėnas, Mindaugas Dagys,

Rita Norvaišaitė

The authors assume sole responsibility for the content. The content of this publication does not necessarily reflect the opinion of the European Commission. © Darius Daunys, 2015 © Žymantas Morkvėnas, 2015 © Saulius Karalius, 2015 © Translation into English. Mantas Zurba, 2015 ISBN 978-609-8041-16-3

THE BOOK OF THE SEA

Salinity Food chain Ice cover Water currents

The realms of the Baltic Sea 33 The swash zone 39 Bladder wrack 39 Sand hopper 40 Gulls 40 Common gull 42 European herring gull 42 Great black-backed gull 44 Terns 45 Sublittoral sandy slopes 51 Baltic macoma 51 Sand gaper 53 Lagoon cockle

Lithuanian Sea Museum

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Water balance

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Table of Contents

54 Brown shrimp 54 Relict amphipod 55 Relict isopod crustacean 57 Small sandeel 58 Turbot 59 European flounder 60 Velvet scoter 60 Common scoter 63 Reefs 71 Black carrageen 71 Green branched weed 72 Bay barnacle 73 Mussels 75 Rockpool prawn 75 Baltic isopod 76 European eel 77 Atlantic cod 78 Three-spined stickleback 79 Shorthorn sculpin 80 Lumpfish 80 Eelpout 82 Freshwater fish 84 Round goby 85 Steller’s eider


86 Long-tailed duck 87 The water column 93 Phytoplankton 95 Zooplankton 95 Opossum shrimp 96 Twaite shad 97 Baltic herring 98 European sprat 100 European whitefish 101 Vimba bream 102 European smelt 103 Atlantic salmon 104 Goosander 104 Red-throated loon and Arctic loon 106 Great crested grebe 107 Auks 109 Grey seal 111 Harbour seal

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112 Ringed seal 114 Harbour porpoise 115 Deep water depressions

and dead zones

121 121 122 122 124

Filamentous chemotrophic bacteria Scoloplos armiger Pontoporeia femorata Diastylis rathkei Ostracods, or seed shrimps

Preface

The word ‘Baltic’ holds many associations of great importance to us ranging from our childhood memories about splashing in the spatter of the sea and building sand castles, to the Baltic Way–the symbol of our freedom and unity. This is a part of our history and an invaluable treasure. However, contrary to the citizens of many other maritime countries, a few of us are used to fully enjoy the presents of the Baltic Sea, and our acquaintance with it is often limited to summer holidays at the beach. We have very few possibilities and occasions to see the unusual sea life that takes place at some depths. Only a handful have been lucky enough. They say that personal encounters with nature and the experiences they bring make people realise the great importance of nature and the necessity to preserve it. So how can we get to know the different realms of the Baltic Sea hidden beneath the waves, often far away from the shore? Why should we care and try to preserve some mollusc colonies perching on deeply submerged boulders if we are likely to never see or touch them? This book is an opportunity to learn more about the Baltic Sea, its extraordinary and unique life. To see it with the eyes of the authors of different chapters, many of whom have spent countless hours at the sea bottom, on research vessels, observing sea birds or exploring variety of fish. The authors tried to introduce the marine inhabitants in such a way that they become familiar to the reader and provoke curiosity. The book is not an academic work or a textbook. The data and stories given here are just some interesting facts about our sea and its dwellers. Of course, this is only a glimpse of the secrets guarded by the sea sustaining more than 6 000 species, whose life stories have been covered by thousands of scientific articles. Acquaintance with the Baltic Sea starts in this book with the introduction to the ecosystem of the Baltic Sea and its most important and interesting characteristics. Then the reader is invited to take a closer look at several marine habitats, which we poetically compared to

Nature conservation 127 Why is it necessary to

protect nature?

131 The principles and tools of

nature conservation

134 Protected marine areas

in Lithuania

141 References 145 Index

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Preface


different “realms”, and their prevailing dwellers. Each described species or group of organisms are presented also in unique illustrations by Saulius Karalius, who is both an artist and a biologist. We hope that his meticulous approach will adequately reflect the artist’s respect towards these creatures of the sea and his insatiable curiosity to discover their stories. The last section of the book is dedicated to nature conservation and offers an overview of our protected marine areas. It is not very important, which section of the book you will choose to start the acquaintance with the Baltic Sea, and how much you will be able to read at a time. By spending just a few minutes, you will be able to learn about one of almost sixty species or larger groups of marine organisms, while by spending more time you might be able to explore one of the five presented submarine realms or discover some unique characteristics of the Baltic Sea. This book is dedicated to both youngsters and adults, to those relaxing on the Baltic beaches or those shopping at the fish market. To people engaged in natural sciences and to those exploring charts in search for travel destinations and adventure. It is equally good for a quiet evening with a book or some lazy time at the sea coast.

Ecosystem of the Baltic Sea

Žymantas Morkvėnas, Darius Daunys

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9

Preface


Geological development of the Baltic Sea In comparison with geological development of the oceans and some other seas, spanning hundreds and tens of million years, the Baltic Sea is very young, practically in its “babyhood”. Its origins date back some 400 thousand years, in the so-called Holstein interglacial stage, while the seabed similar to the present one has formed even later, in the Eemian interglacial, some 132-120 thousand years ago. The key factors which determined the formation of the Baltic Sea depression are thought to have been tectonic movements of the Earth’s crust and erosive impact of the Scandinavian continental glaciers, that have covered this region several

Baltic Ice Lake with its northern part

The Yoldia Sea (11.6–10.7 thousand years ago)

bordering the melting glacier

Its typical species, the bivalve mollusc Yoldia arctica

(13.0–11.6 thousand years ago)

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G e o lo g i c a l d e v e lo pm e n t o f t h e Ba lt i c S e a


before present. The name of the sea originates from the Latin name of mollusc Yoldia arctica, which once inhabited the cold and saline basin. With the intensive crust rebound in Scandinavia, the link between the World Ocean and the Yoldia Sea had disappeared, and the latter was replaced by Ancylus Lake, which lasted between 10.7 and 8.3 thousand years before present. The water temperatures of the lake were relatively low, as the lake was partly fed by the melting remnants of Scandinavian glacier. The name of this water body originates from the freshwater mollusc Ancylus fluviatilis, discovered in the sediments of that period. The Litorina Sea emerged some 8.3 thousand years ago, as a new connection with the North Sea opened up in the area of current Danish Straits, and saline water from the World Ocean flushed into Ancylus Lake. This process was caused by the sinking of the Earth’s crust in the southern part of the modern Baltic Sea, as well as by intensive rise of the global water level. The Litorina Sea stage was characterised by higher salinity than nowadays, which made it a suitable habitat for the mollusc Littorina littoraea, that later gave its name to the sea. It was at this stage, that the Curonian Spit was formed and amber was washed from the Sambia Peninsula into the sediments of the Lithuanian Baltic coast and the Curonian Lagoon. Nowadays, its pieces are occasionally cast ashore by waves and sea currents. Approximately 3.7 thousand years ago, as the intensity of geological processes had subsided, a relatively steady water level and the present coastlines stabilised. This period is called the Post-Litorina Sea. The development of the modern Baltic Sea covers the last 700 years.

times. The modern Baltic Sea has also undergone a complex geological evolution since its occurrence after the last glaciation till present, alternating its state between an isolated fresh water body and a brackish sea with a connection to the World Ocean. This succession was determined by the melting dynamics of the last Scandinavian continental glacier and associated post-glacial rebound of the Earth’s crust, global climate warming and massive melting of the ice sheet, followed by the rise of the global sea levels, as well as by crust fluctuations within the Baltic region and certain other processes. The modern Baltic Sea began to emerge only after a significant part of the ice sheet, produced by the latest Scandinavian continental glaciation, had melted. The first stage in the formation of the Baltic Sea was Baltic Ice Lake, which covered the southern part of the Baltic Sea depression between 13.0-12.6 and 11.6 thousand years before present, feeding mainly from the melting glacier covering the northern part of the depression. The next stage was the Yoldia Sea, which occurred with the spillover of Baltic Ice Lake and formation of the connection with the World Ocean in the territory of current Central Sweden. This marine basin lasted almost a millennium, approximately from 11.6 to 10.7 thousand years

12

Ancylus Lake (10.7–8.3 thousand years ago)

The Litorina Sea (8.3–3.7 thousand years ago)

Its name originates from the freshwater mollusc

The marine gastropod mollusc Littorina littorea was

Ancylus fluviatilis which inhabited the lake

widespread during this stage

THE BOOK OF THE SEA

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G e o lo g i c a l d e v e lo pm e n t o f t h e Ba lt i c S e a


The coasts of the Baltic Sea

Prevailing coast types in the Lithuanian coastline of the Baltic Sea A. Increasing (accumulation) and stable coast Protective dune crest

Berm crest

The Baltic Sea is characterised by a relatively high coastal diversity. In the northern and western parts of the Baltic Sea, bordering Scandinavia and the Jutland peninsula, where hard crystalline or sedimentary rocks resistant to wave erosion prevail near the land surface, the existing landscape has been shaped by erosive impact of the continental glacier and, to some extent, by accumulative processes at the end of glaciation. The coasts on that side were formed as the sea flooded the contour of post-glacial landscape. Tectonic processes are also important to their development: the post-glacial rebound of the Earth’s crust is most obvious in the northernmost part of the Baltic Sea, the Gulf of Bothnia, where it reaches 9-10 mm per annum. All these factors determine, that the northern and western coastline of the Baltic Sea is predominated by the fjordic coasts, with elevations ranging from several to tens of metres, which produce multiple inlets, bays and quite often even fjords or sounds, projecting up to a dozen or so kilometres into the land. The south-eastern Swedish and southern Finnish coastline of the Baltic Sea is characterised by the skerry coasts, consisting of a multitude of larger or smaller islets and rocky reefs. Skerries are widespread along the Swedish and Finnish coasts producing an aggregation of islets called the Archipelago. The latter covers the area of 11 000 km2 and consists of more than 24 000 islands and islets, being one of the most numerous in the world. Completely different types of coast prevail at the southern and eastern Baltic coastline. In that part of the basin, the coasts mainly consist of sediments and deposits of diverse origin: fluvial, organic, aeolian, etc. The prevailing soils are morainic clay and sandy loams, cobble and gravel, sand, silt, clay, and, in certain locations, peat, sapropel deposits, etc. These are soft or even crumbly formations, therefore those parts of the Baltic coastline are shaped by waves and currents. Fluvial deposits also play an important role in coastal formation processes in the southern part of the Baltic Sea, as well as on the eastern side of the Gulf of Finland and in the Gulf of Riga, resulting in flat coastal-alluvial plain coasts with extensive beaches.

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THE BOOK OF THE SEA

Dune slack

Beach face

Longshore sandbank Longshore trough

Dunes

B. Abrasion coast subject to wave erosion Cliff

Sandbank

Morainic plain levelled out by waves and currents

Sand

Moraine

15

Boulders and cobble

T h e c oa sts o f t h e Ba lt i c S e a

Ancient sea coast and terrace


The Yoldia Sea coasts nowadays are hidden by the Baltic waters–they are a few tens of metres below the present sea level. The former existence of dry land in the place of current sea bottom and the ancient coastline are indicated by rather steep terraces in the bottom relief, as well as by casual remnants of trees (stumps or trunks), dating back some 11-10 thousand years. The Ancylus Lake shoreline is also submerged in the Baltic Sea waters, just like that of its predecessor, the Yoldia Sea. Its position is vaguely determined and remains the object of scientific discussions. Future geological studies of the Baltic seabed should help to reveal the true position of the Ancylus Lake boundaries. The most conspicuous of the ancient coastlines in Lithuania is that of the Litorina Sea. In some areas it is represented by a flat coastal ridge situated some 7-8 m above the present sea level, for instance at Būtingė, in some other locations, like Nemirseta or Olando Kepurė (Duchman’s Hat) cliff, it turns into a steep slope over 10 m high. The subsequent Post-Litorina Sea in most cases remained within the earlier boundaries, however, in some segments of our coastline–north of Palanga or in the proximity of Birutės Hill–one can find the relics of the previous basin immediately behind the current ridge of the coastal dunes: segments of a slope hardly reaching 2 m. In the modern Baltic coastline of Lithuania, an obvious difference exists between the Curonian Spit and the continental coast. The Curonian Spit coast is flat and sandy, and a manmade protective coastal ridge shaped in the 19th century runs along its full length. According to its dynamic status, this coastal segment can be classified a stable coast (Fig. A). On the continental part, flat beaches framed by coastal dunes and segments of the terraces from ancient basins interchange with steep cliff segments. The coasts are in different dynamic states. Most of them are stable coasts, which means that the sediments washed away by storms are restored during calm periods. Significant areas of the coastline, especially on the continental part, are subject to wave erosion (Fig. B), for instance at Olando Kepurė cliff, or at somewhat lower cliff near Šaipiai. The least widespread type in Lithuania are the coasts with predominant accumulation of sediments, or the socalled accretional coasts.

Estonian coast of the Gulf of Finland

In the southern part of the Baltic Sea, sand is carried along the shoreline by sea currents and waves, thus producing sand spits and shallow lagoons separated by them from the sea, so-called boddens (the Bay of Greifswald, Szczecin Lagoon, etc.). In the south-eastern part of the Baltic Sea, several relatively massive sand spits usually featuring well-developed dune landscapes separate from the sea larger, mostly freshwater lagoons. The south-eastern Baltic area, including the Lithuanian coastline, is characterised by abrasion coasts (subject to wave erosion), accumulation coasts (increasing over time) or abrasion-accumulation coasts with frequently alternating eroded and expanding coastal segments. In the recent geological past, the Lithuanian part of the Baltic coastline has often changed its position and configuration. The remaining shoreline segments of the previous historical basins contribute to our understanding of geological development of the Baltic Sea in the post-glacial period, i.e. approximately in the last 13 millennia. The oldest Baltic Ice Lake shoreline is most distinctive at the Lithuanian seaside area to the north of the city of Klaipėda, where its segments are situated at 6-7 m. altitudes above the current sea level, whereas near Būtingė they are located higher–at 15-16 m.

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17

T h e c oa sts o f t h e Ba lt i c S e a


Water balance

The Baltic Sea contains some 20 800 km3 of water. If all of it were fresh, it would provide drinking water for the present global human population for about 4000 years. A water balance equation, describing water input and loss, could be derived for the Baltic Sea, just like for any other water body. Freshwater input is provided by the rivers, collecting it from extensive areas called river basins. Together, they comprise the Baltic Sea basin covering the area of 1 633 290 km2, which is four times the size of the sea surface alone. Some 250 rivers provide the annual inflow of 440 km2 of fresh water, which would cover the Baltic Sea surface with a layer 1.17 mm thick. The groundwater inflow accounts for at most 0.5 % of the total water mass of the Baltic Sea, therefore this inflow is usually counted as part of the input provided by rivers. The major input is provided by the River Neva, followed by somewhat smaller contributions by the Vistula, the Daugava, and the Nemunas. The highest input from the rivers is in spring, when snow is melting. The Baltic Sea basin holds the human population of some 85 million, therefore water from the drainage area also brings to the sea a surplus of nutrients causing the process of eutrophication, as well as various contaminants that water treatment facilities fail to remove. Another source of water input to the Baltic Sea is precipitation, which accounts for almost 20 % (225 km3) of the total input in the water balance. Of course, precipitation is highly dependent on the changing climatic conditions, but, on the average, the Baltic Sea annually receives some 500–600 mm of precipitation. The maximal input from precipitation is in July-August, the minimal–in February-March. Precipitation adds to the Baltic Sea not only fresh water but also various elements and substances, such as dissolved nitrogen. But, contrary to the river input, these substances and elements are brought from areas beyond the boundaries of the Baltic Sea basin. The Baltic Sea also has a connection with the North Sea via the Danish Straits which have limited flow capacity. They allow the annual inflow of some 1 180 km3 of saline sea

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Boundaries of the Baltic Sea basin

19

Water balance


water, which is almost three times more than the input provided by the rivers. The highest input from the North Sea is in November-January, while the lowest–in May. The inflow of saline water depends on the pressure gradient and on the winds that push water from the North Sea into the Baltic. This inflow brings along marine organisms characteristic to more salty waters. The negative part of the water balance consists of the loss through evaporation and the outflow from the basin. The annual evaporation from the Baltic Sea is very close to the input by precipitation. The estimated annual evaporation is some 450–500 mm, or about 175 km3 of water. The least intensive loss by evaporation is in spring, when the sea surface temperature is still relatively low and the winds are not so strong. The highest evaporation rate is in late autumn. Due to higher surface temperatures and a shorter cold season (when the sea is covered with ice), the southern part of the Baltic Sea looses more water by evaporation than the northern one. Because of lower density, the brackish water of the Baltic Sea flows into the North Sea along the surface layers of the Danish Straits. This way, the Baltic Sea looses about 1 660 km3 of water annually. Although the intensity of water exchange between the North Sea and the Baltic Sea varies greatly by month, by season, and by year, a complete water replacement in the Baltic Sea takes on the average about 25 years. In the neighbouring North Sea, for comparison, complete water turnover is reached in approximately 2 years.

Salinity

Change of the diversity of freshwater, brackish water and saltwater species along the water salinity gradient (Remane diagram)

No of species

Baltic Sea

0

10

20

Salinity (‰) Freshwater organisms Brackish water organisms Seawater (saltwater) organisms

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21

Sea water contains all the elements known on Earth, most of them as the ions of different salts (NaCl, MgCl2, K2SO4, CaCO3, etc.). The concentration of dissolved salts is defined as water salinity. The major input of salts is provided by rivers, but winds and precipitation also contribute to some extent. Large amounts of salts get into sea water from hydrothermal vents and submarine volcanoes, as well as from dissolving seabed and coastal rocks. The low salinity of the Baltic Sea is determined by the two main factors: its geographic position, resulting in limited water exchange with the Atlantic Ocean, and the substantial fresh water input by rivers. Compared to the average ocean salinity, the Baltic water salinity in its central part is full five times lower, so the Baltic Sea is considered a brackish water basin. Brackish water is defined as salty water, whose salinity exceeds that of fresh water but is much lower than that of the ocean. The major input of salts into the Baltic Sea is provided by the saline water flow from the North Sea via the set of straits: Skagerrak, Kattegat, the Great Belt, the Little Belt and Øresund (Öresund). These straits have the highest water salinity in the Baltic area. If at Kattegat water salinity reaches approximately 30 ‰ (about 30 g/l), in the Gulf of Finland and Bothnian Bay salt concentrations are merely 2.5–4 ‰, and in some north-eastern straits or bays the water may be 30 40 50 completely fresh. At the Lithuanian coastline, water salinity usually reaches 7–8 ‰. This is the salinity one would obtain by dissolving about a teaspoonful of salt in 1 l of water. Because of the inflow of fresh water and water exchange with the Atlantic Ocean, the Baltic Sea has rather distinctive

S a l i n i ty


stratification. Stratification of the water column is determined by the density gradients between more and less saline water layers. Diluted waters of lower density stay at the surface, while heavier saline waters sink deeper. These water masses are separated by a special stratum of steep salinity shift (halocline), characterised by a sharp increase in salinity across the layer. The halocline is usually situated at the depths of 40-80 m. In Lithuanian waters it is at 60-80 m, the salinity changing from 7–8 ‰ above to 10–12 ‰ below it. The steep salinity gradient strongly restricts mixing between the surface and deep water strata preventing transportation of the oxygen-saturated surface waters into the depths. Salinity characteristics of the Baltic Sea cause a very specific biological diversity. Although the number of species is relatively low, the Baltic Sea holds a unique combination of organisms typical to both saltwater and freshwater habitats. With increase of salinity, the diversity of freshwater species declines, while that of saltwater species tends to grow. The biodiversity gradients of both groups of organisms are illustrated by the Remane diagram produced by German marine biologist Adolf Remane in 1934. This diagram suggests that the lowest diversity of marine organisms falls in the salinity interval of 5–8 ‰ (typical to the central Baltic Sea, including Lithuanian waters). The Baltic Sea salinity, gradually decreasing from Skagerrak all the way northwards, determines distribution of some typical marine species. For example, starfishes and sea urchins do not inhabit central and eastern parts of the Baltic Sea. Water salinity affects not only physical characteristics of water and the distribution of aquatic organisms, but also their reproduction, growth rates, etc. Thus spawning of cod is successful under salinity of at least 10 ‰, and with the salinity gradient between 18 ‰ (Bay of Kiel) and 8 ‰ (Lithuanian coast), the maximum size attained by Mytilus mussels decreases from 8-9 to 3.5 cm. Salinity is extremely important to aquatic organisms, because it regulates the osmotic pressure of their bodily fluids, and thus determines the direction and speed of diffusion of various salts and dissolved gases. The balance of elements and substances necessary for normal life functions depends on these processes, therefore some species absorb salts from the environment, some prevent them from entering their organisms, while the third group maintains the same salinity levels as the surrounding water. Marine species cannot exist under low salinity, and to many of them the Baltic Sea water is too diluted, while to many freshwater species it is already too salty.

Distribution range of key Baltic Sea species Baltic macoma Cod Bladder wrack Mussel

5

Common jellyfish European flounder

3 5

4

6 30 Common limpet

20 7 10

Common starfish

8

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THE BOOK OF THE SEA

Common shore crab

Source: HELCOM, 2010

Common periwinkle Green sea urchin

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S a l i n i ty


Food chain

0,01 % 0,1 % 1 %

A marine ecological food chain is a system of organisms linked by trophic connections, wherein energy is transmitted from the producers (phytoplankton, aquatic plants and algae) through the upper trophic layers all the way to the apex predators–birds and mammals feeding on fish. Only about 10 percent of all energy produced at any individual trophic layer is passed onto the next layer. Because of this significant energy loss, food chains are usually limited to 5-6 trophic layers. In the offshore parts of the Baltic Sea, the prevailing type is a relatively simple pelagic Dynamics of sprat and food chain consisting of phytoplankton, planktonic crustaceans (zooplankton) feeding on it, plankton-feeding fishes, such as sprats, and predatory fishes, such as cods. Out of the breeding cod stocks in the Baltic Sea season, offshore areas also host fish-feeding birds, such as murres, razorbills, gulls, etc. In coastal waters, trophic 40 20 relations are more complex, comprising a food web consisting of numerous interlinked alternative food chains. There, 30 15 the diversity of primary energy sources is higher, and the systems include abundant benthic invertebrates and demer20 10 sal fish communities feeding on them. The invertebrates are also consumed by wintering sea ducks, while the fishes are 10 5 preyed upon by seals, divers, grebes, sterns, gulls, etc. The Baltic Sea food-chain is very volatile and vulnera0 0 ble. In offshore waters, cod is the key species influencing the dynamics of abundance of many other organisms. Back in 1975 1980 1985 1990 1995 2000 2005 the middle of 1980s, cod populations had collapsed because of overfishing and disrupted recovery of stocks due to Sprat stocks (1010) Cod stocks (108) decreased salinity and oxygen deficiency at the spawning Source: ICES 2005a

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THE BOOK OF THE SEA

Large (apex) predators Seal, harbour porpoise

Predators Cod

Secondary consumers Plankton-feeding fish

Energy transfer between different trophic levels

10 %

in marine ecosystems

100 %

Primary consumers, herbivores Zooplankton

Producers Phytoplankton

grounds. This had a broad-reaching effect on all trophic layers. The decline of cod population resulted in the explosion of the Baltic herring and sprat stocks. These reduced the numbers of zooplankton, thus indirectly triggering a burst of phytoplankton growth, the so-called “algal bloom”. The increased densities of sprats also intensified their intra-specific competition for food, resulting in lower weight of individual fish and lower quantities of fat (i.e. energy) accumulated by them. Some sea birds, such as common murres, are adapted to consume only high energy food, and, as a consequence, significant slowdown in growth of their young was observed.

25

Food chain


Ice cover

Parts of the Baltic Sea that freeze over in winter Mild winter Regular winter Unusually cold winter Ice-free part of the Baltic Sea

Ice cover occurs in the Baltic Sea each year. The traces of ice can be found as long as seven months per year, therefore it is very important for physical and ecological conditions in the basin. Due to the low water salinity, the Baltic water starts freezing at the temperatures just below 0 ºC. Ice formation usually starts in mid-November in the northern part of Bothnian Bay and gradually extends southward. The maximum ice cover is reached in February-March, hiding about 45 % of the total sea surface. The Gulfs of Bothnia, Finland and Riga usually freeze completely, the edge of ice cover passing near the Stockholm area. To the south of that boundary, in normal winters ice covers only shallow coastal waters, such as the Curonian Lagoon, Vistula Lagoon, Szczecin Lagoon and parts of the Danish Straits. A complete freeze-over of the Baltic Sea happens only in extremely severe winters. The last case was registered in 1947, while in winter of 1987, ice covered about 96 % of the total surface of the sea. However, even in such extreme conditions, the central part of the Baltic Sea remains open, or the ice cover is very thin there. With the increasing intensity of shipping, ensuring continuous operations of the Riga, Tallinn and other northern Baltic ports is very important. A fleet of some 20-25 icebreakers is engaged in the task. The ports of Klaipėda, Liepaja and Baltijsk are considered as ice-free ports, because the ice cover, if it ever forms there, is thin and shipping is possible without the aid of icebreakers. As the sea ice reaches the thickness of 22 cm, the longest ice road in Europe opens in Estonia. It connects the port of Rohuküla and the island of Hiiumaa stretching for about 26 km. Travelling on ice roads is part of historical and cultural heritage of Estonian islands. The Baltic ice cover is very important to the ringed seal, because these animals are adapted to reproduce on ice. They dig burrows wherein the pups are born and raised. Shrinking of the ice cover, caused by warmer winters in recent decades, poses threat to the survival of this species.

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Helsinki

Oslo Stockholm

Tallinn

Riga Copenhagen Klaipėda

27

Ice cover


Water currents

Main circulatory routes of water masses in the Baltic Sea Surface water masses

Water masses in seas and oceans are transported long distances by continuous, directional movements of water called currents. Under the influence of the rotation of the Earth, the Baltic Sea currents flow counter-clockwise. The currents passing the south-eastern Baltic coast are heading north and north-east, and their branches diverting towards the Gulfs of Riga, Finland and Bothnia retain general directional trend. They are charged with additional energy by the rivers falling into the sea in these gulfs before returning into the main system of marine currents. Having reached the northernmost part of the Baltic Sea, the currents change their course and flow south towards the Danish Straits along the eastern coast of Sweden. The main factors, causing circulation of water masses, are wind, water density gradient and the flow from the rivers. Winds bring into movement the surface layers of water, whereas the density gradient and associated differences in mass cause turbulence in the deeper layers. The speed of permanent currents in the Baltic Sea reaches only 3-4 cm/s (sometimes up to 10-15 cm/s). During the autumn and winter storms, the velocity of currents may increase significantly, up to 1-1.5 m/s. The deep water currents of the Baltic Sea never flow faster that 3-5 cm/s, therefore fresh water from the Great and the Little Belt may take from half a year to a full year to reach the Åland Islands in the northern part. The maximum current velocity in Lithuanian coastal waters was registered on 11-14 November 1967, in front of Giruliai, at the depth of 33 m. The wind speed then reached 25 m/s and the current velocity was 74 cm/s. The system of Baltic currents is highly dependent on water circulation at the Danish Straits. There, the water movement is rather complicated because of the mixing of fresh and saline water, stratification of the water column, complex contour of the seabed and frequent weather changes. When the weather is still at these straits, the surface layer of the brackish Baltic Sea water flows into the North Sea, while the more dense and saline water from the North Sea flows along the bottom in the opposite direction. There is no stratification of currents in the Øresund

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THE BOOK OF THE SEA

Source: Omstedt et al., 2013

Deep water masses

29

Water currents


strait, because the shallow sills of Drogden and Darss hinder the inflow of denser water from the North Sea into the Baltic Sea. However, the situation may change under the strong western or south-western winds, because they might cause significant flow of the North Sea water resulting in the water surge at Skagerrak and Kattegat, and as a consequence, saline water may sweep into the Baltic Sea not only along the bottom but through the entire cross-sectional area of the straits, also rolling over the Drogden Sill and the Darss Sill. A reverse process is also possible, when prevailing eastern winds cause water surge on the Baltic side. The Curonian Lagoon water level is usually higher than that of the Baltic Sea, therefore prevailing current in the Klaipėda Strait is flowing outward, carrying fresh water masses from the lagoon into the sea. Under gale-force northern or north-western winds, the current shifts its direction because of the surge of the Baltic Sea waters, and the brackish water whooshes into the lagoon. In extreme cases, the sea water may reach as far as the Cape of Ventė or the town of Nida, forcing the freshwater fish of the Curonian Lagoon to retreat. It is quite likely, however, that this retreat of fish is mostly caused by the lower temperature of incoming water, rather than by its higher salinity. Currents are of great importance. They ensure circulation and mixing of huge water masses thus changing the distribution patterns of salinity and oxygen concentration. Currents also participate in coastal formation and some even in climate formation processes, they transport nutrients and marine organisms lacking active mobility.

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The realms of the Baltic Sea

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Water currents


The swash zone

This is the borderline of the marine world. To us, the sea begins here, while to the marine inhabitants here it ends. To many holiday makers, this world reminds promenades on the beach with the waves gently tickling their bare feet, while they scan the shore with their eyes in attempt to spot a piece of amber or some other sea treasure among shiny pebbles, shells washed ashore, piles of fancy seaweeds and polished shards of glass. Treasures do exist there. However, a very few people have heard of them and even less have actually discovered them. 32

THE BOOK OF THE SEA

33

The swash zone


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35

The swash zone


B

A

D C

A

Black-headed gull

B

Common tern

C

Amber

D

Black carrageen

Sand hopper, also known as the “sand flea”, sitting in its burrow

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37

The swash zone is the most volatile part of the beach, where the waves breaking against the shoreline carry sand and create a link between the beach and the sea. Measured from the shoreline up, the swash zone may encompass up to 20 m of the beach during storms, while in the calm weather it would shrink to a mere few centimetres. In spite of that, the traces of previous storms are almost always present around: little pools, washed ashore gravel, piles of seaweeds and shells, and some rubbish, accidentally swept from ships or thrown into the sea by people. Because of recurring storms and irregular flooding, when the same part of the beach becomes either submerged or dry, the swash zone might appear to have neither characteristic fauna nor flora. Only occasionally, usually right after storms, one can see with a naked eye a few “emigrants” from the sea–amphipods, washed ashore together with the clusters of seaweeds, ripped by the storm from boulders on the bottom. Even rarer sighting on the sandy beach are the only macroscopic leaping crustaceans, adapted for permanent life in this zone, also called “sand fleas” (Talitrus saltator). A very few visitors coming to enjoy the beach know that deep underneath (0.3 m deep in summer and up to 0.5 m in winter) entire colonies of these crustaceans may be thriving. In the safety of night, when predators are absent, these arthropods would usually crawl to the surface to feed. Those, thinking that the swash zone holds nothing else but sand and some sea sediments, would be surprised to learn, that among particles of sand, where

Th hee sswa wa sh s hz oznoen e


Coarse sand with some

Bladder wrack

gravel granules and pebbles.

(Fucus vesiculosus, Linnaeus, 1753)

The latter consist of hard crystalline rock particles of relatively high resistance to mechanical destruction Well separated medium sand with prevailing quartz particles

moisture is captured, dwell rich communities of tiny animals, usually smaller than 0.5 mm across. They are also known as meiofauna. The diversity of these little organisms might in some cases be up to 25 times higher than that of macroscopic organisms seen with a naked eye. These animals exploit the cavities existing between sand particles, whose volume may account for up to the 40 % of the total volume of sand. Such communities play a unique role by decomposing the organic matter accumulated in the sand, and thus making an invisible contribution to the clean-up of beaches. In winter, as temperatures drop below zero, even the scarcely observed life disappears from the swash zone, while the animals that hide in the sand retreat into deeper layers. Sometimes air temperature is the only factor determining the location of the swash zone for the next spring. Ice cover along the shoreline protects the sand against strong storms quite efficiently, increasing probability that the swash zone will remain unchanged. However, in warm winters sandy beaches can be heavily eroded by powerful storms, so the next season both the swash zone and all its associated communities develop in new locations, although the key species and their interactions with the environment remain the same. Only a handful of holidaymakers would have sufficient knowledge of the swash zone to notice the difference.

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T JŪ H ROS E B O KONK YOG FA T H E S E A

The bladder wrack is a khaki-coloured brown alga, abundant on the rocky shores where it grows attached to hard substrates. In the Baltic Sea, it is most abundant near the Swedish and Finnish coasts. This brown alga does not grow in Lithuanian coastal waters because of strong swells during storms, however, one may find beached fragments of bladder wrack brought by the sea from other areas. The frond is flat and branching, and it usually holds numerous spherical air bladders. These bladders help the fronds to float closer to the surface and increase the overall surface area important for photosynthesis. Dependent on the temperature, impact of waves and currents, and the luminance at the bottom level, the growth rates of bladder wrack may vary between 0.05 and 0.14 cm/day, the maximal length reaching about 2 m. The life span is 4-5 years. Dense fields of bladder wrack provide an important substrate and shelter to other species, including malacostracans (or higher crustaceans), worms and snails. Since 1811, Fucus vesiculosus has been renown as one of the key sources of iodine, which is necessary for the production of hormone thyroxine, and it has been used to treat multiple conditions, such as thyroid disorders, inflammation of joints, etc. These macroscopic algae are a valuable source of many other important micro elements: calcium, magnesium, sodium, potassium, iron, chromium, zinc, as well as vitamins A, C, E, B, etc., therefore bladder wrack is used by beauty industry as a substance regulating skin elasticity. A Japanese study, carried out in 2005, revealed that bladder wrack can suppress the production of hormones which increase the risk of breast cancer.

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The swash zone

In eastern countries, bladder wrack also is a common food ingredient. The main active substance produced by bladder wrack is alginic acid, used by the food industry as a natural thickening agent for drinks, ice creams or soups.

Sand hopper (Talitrus saltator, Montagu, 1890) Talitrus saltator is a terrestrial amphipod widespread in north-eastern and northern Atlantic, Baltic and Mediterranean regions. They are most common at the tidal zones of sandy beaches, where they dig 10-30 cm deep into the sand during the daytime to avoid dehydration (desiccation), while at night they resurface to feed on decaying algae or other macroscopic plants washed ashore. These dull brown or greenish amphipods have one pair of black eyes, and two pairs of antennae, one of them being


ever taken a ferry to cross to Smiltynė (Curonian Spit)–most of the birds following the boat would be the black-headed gulls. In summer, the best identifiers of this species are dark brown head and dark red legs and beaks. Beyond the breeding season, the dark head colouration is lost, only a few dark spots remain, especially around the ears. During migration and in winter, the diversity of gull species increases, especially at the sea coast–up to 10 different species can be observed then. The identification of different gull species requires some skills, as their overall appearance is usually very similar, the differences being in the size, the colour of legs and bills, and the behaviour. Juvenile birds are even more difficult to distinguish, because they take several years to attain the appearance of adult birds.

thicker and longer than the other. The females are slightly smaller than the males. Talitrus saltator is sometimes known by its popular name of the “sand flea” because of its leaps sometimes reaching almost 1 m, produced by a flexion of the abdomen. The direction of leaps is not controlled, therefore sand fleas usually repeat a sequence of several leaps in order to escape into safety. Nocturnal migration of sand hoppers (or sand fleas) Common gull deeper into the dry land, where they feed on decomposing (Larus canus, Linnaeus, 1758) algae, is most active a few hours past midnight and continues till sunrise. There is scientific evidence that amphipods use the The common gull is a usual visitor at the coastal area during position of the Sun and the Moon to assess the time of the day. migration and in winter, but it also breeds in Lithuania. This The highest density of terrestrial amphipods on the species is broadly widespread in the whole of Eurasia and Lithuanian coast is observed in September, reaching some western part of North America. In Lithuania, it breeds in low 280 adult individuals per square metre. numbers in different parts of the country, somewhat bigger colonies settle on the island of Lake Kretuonas. In winter, Gulls it is common at the Lithuanian coast. Feeds on various invertebrates and small fish, both at sea and on land. As Almost 20 gull species have been registered in Lithuania, but many other gull species in Lithuania, the common gulls may about a half of these are only casual migrants. Only five speoften turn to scavenging at landfills. The size is significantly cies of gulls breed regularly in our country, the most abunlarger than that of the black-headed gull, from which it also dant of them being the black-headed gull (Chroicocephalus differs by greenish-yellow bill and legs. During the breeding ridibundus), breeding in large colonies in different parts of season, the head of the common gull is bright white, while in the country. This species is well familiar to those who have autumn and winter it turns greyish with some spots.

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Common gull

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The swash zone


European herring gull

Great black-backed gull

(Larus argentatus, Pontoppidan, 1763)

(Larus marinus, Linnaeus, 1758)

Another regular gull species in Lithuania is the European herring gull. The range of this species spans from the Kola Peninsula and northern parts of Norway in the north to the French coasts of the Atlantic Ocean in the south. The first breeding pairs were registered in Lithuania just over 30 years ago on Kiaulės Nugara Island in the Curonian Lagoon. Since then, the number of breeding pairs has been gradually increasing, and at present some 200 pairs of the European herring gull breed all over the country. At the seaside, this species is common both during the migratory and wintering seasons. The European herring gull is somewhat similar to the common gull, but is much bigger, has a more massive yellow beak with a red dot on its lower mandible, and pink legs. Two other gull species related and very similar to the European herring gull are also found in Lithuania: the Caspian gull (Larus cachinnans) also breeding in Lithuania in low numbers, sometimes together with herring gulls, and the yellow-legged gull (Larus michahellis) which does not breed in Lithuania but is a regular visitor.

The largest of all gull species regularly encountered at the Lithuanian coast and one of the largest gull species worldwide is the great black-backed gull, whose wingspan may reach 1.7 m. It differs from the European herring gull not only by its size, but also by much darker back and upper side of the wings. Another typical marine gull species worth mentioning is the black-legged kittiwake (Rissa tridactyla). This bird does not breed in the Baltic Sea area, however, lately it has become a rather common visitor. The first sighting in Lithuania was registered in 1982. This species is seldom seen from the shore, being a typical offshore (pelagic) species, spending somewhat more time on land only during the breeding season. In Europe, it breeds on the shores of the North Sea, Atlantic Ocean and Barents Sea, usually gathering in huge colonies on the coastal cliffs where the nests lie less than a metre apart. Their prevailing food are marine invertebrates and fish. The little gull (Hydrocoloeus minutus), as suggested by its name, is the smallest gull species not only in Lithuania, but also worldwide. This species is a rare breeder in our country included in the national Red Data Book and also protected in the entire European Union. At the seaside, it is often observed on migration, in late July–August. Migrating birds are easy to recognise by their dark underwings, rounded wing tips and light undulating flight pattern, especially during foraging, when the birds pick various invertebrates from the sea surface. During migration, these birds will have already shed their black hoods which distinguish them in the breeding season.

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Sandwich tern

Juvenile European herring gull

Great black-backed gull

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The swash zone


Sublittoral sandy slopes

Terns The most common and most known tern species in our country is the common tern (Sterna hirundo), although its relative, the black tern (Chlidonias niger), is equally abundant. Up to several thousand pairs of common tern breed in Lithuania. Usually they nest in small colonies on islands and islets of lakes, ponds and rivers. They feed exclusively in water, the main prey being small fish, less often–aquatic invertebrates. While foraging, terns often plunge into the water from flight, thus reaching prey a few decimetres below the surface. Because of slightly similar appearance, behaviour and habitats, terns are frequently mistaken for gulls, and vice-versa, especially the common tern and the most widespread black-headed gull. However, these two birds are not so difficult to recognise, both on the ground and in flight. Looking at a perching bird, terns are distinguished by their shorter legs and prolonged body shape due to long wing and tail feathers. A flying tern appears more gracious, with its wings longer and narrower than those of a gull. The bill of a tern is longer and sharper than that of a gull. It is also worth noting that no terns are found in Lithuania in winter– they are long-distance migrants wintering in the southern hemisphere. At the Lithuanian seaside, migrating common terns are quite numerous from the end of summer and through September. At the same time, another close relative of the common tern – the Arctic tern (Sterna paradisaea) – can also be seen. The main difference between the two species is the longer external tail feathers (rectrices) of the Arctic tern, giving its tail a deeper forked appearance. The migrating common terns are usually observed in their winter plumage with a paler “hood” and darker beak.

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THE BOOK OF THE SEA

Common tern

Another tern species, the Sandwich tern (Sterna sandvicensis), can also be observed on migration at the Lithuanian coastline in late summer, July to August. Up to several hundred migrating individuals are usually registered within a season. The Sandwich tern is a large tern species among those observed at the Lithuanian coast, yielding in size only to the Caspian tern (Hydroprogne caspia) from which it clearly differs by a slender dark beak with a light tip (the beak of Caspian tern is bulkier and bright red). It is worth noting, that this tern species does not breed in Lithuania, and its breeding range pattern in Europe is highly fragmented.

Although this realm is hidden under the water, the immediate associations flashing the images of the Baltic sand dunes are not tremendously misleading. Some of those submarine sandy slopes used to be parts of the developing Baltic coasts several millennia ago. In this realm, just as in the dunes of the dry land, the apparently boring sandy surface may share many interesting secrets with those who take a closer look and dig a little deeper into the upper layer of sand particles.

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Sub l i tt o r a l s a n dy s l o p e s


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47

Sub l i tt o r a l s a n dy s l o p e s


A

B C

H

D E

F G

A

Red-throated loon

B C D

E

Small sandeel

Razorbill

F

Relict isopod crustacean Saduria entomon

Baltic herring

G

Brown shrimp

European flounder

H

Opossum shrimps

Variety of benthic organisms and traces of their activities on the sea bottom

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49

The sand that we see on our beaches is not so widespread on the bottom of the sea– the Baltic seabed is predominated by boulders, rocks, clay and silt bottoms. Underwater sandy slopes are common only in the south-eastern parts of the sea, in the Lithuanian, Latvian, Polish and German coastal waters. In the most shallow part, accessible to swimmers, sandy bottom is easily recognised by sand ripples shaped by currents and waves that constantly move the sand. Somewhat deeper, the ripples turn into larger sand bars reaching several metres in height and stretching along the shoreline, that are also known as sandbanks. In different segments of the sublittoral zone, at the depths of up to 10 m, the number of these sandbanks and the troughs separating them varies and they constantly change their position and height. In this zone, where the impact of waves is felt all the way to the bottom, sandy banks are not very suitable for marine life. For species adapted to burrowing in the sand or anchoring in it by their roots, the bottom may be too unstable as the sand moves most of the time. Organic deposits are also scarce, dispersed by the waves during storms, therefore only mobile animals capable to move in from deeper areas are able to feed there, such as small amphipods, juvenile flatfish, and the brown shrimps. In calm summer nights these areas become a feasting ground for young flatfish. They arrive in big numbers to feed on abundant colonies of amphipods. With the break of day, the amphipods disperse to the nearest shelters, while the flatfish retreat into deeper waters.

Sublli tt Sub i tt oo ra r la sl asnady n dy s losple o spes


In the deeper parts of sandy slopes, the impact of waves is less obvious and the seasonal variation of temperature and other living conditions is smaller. Observations by diving or underwater cameras usually show only individual flatfish or gobies, however, a closer inspection would reveal thousands of small burrows, sandy tubes and protruding siphons. The apparently empty sandy slopes and plains actually hide a rich world, wherein life activities are concentrated in the thin surface layer of sand 1‑2 cm deep. Although oxygen does not penetrate deep into sand, the largest benthic organisms can burrow as deep as 20‑30 cm. They survive by extending to the surface long siphons used to pump in water and food, or by moving actively in their burrows and thus inducing water circulation and replenishment. Regardless of how deep this world reaches into the sand, its inhabitants–bivalve molluscs, priapulid worms and various polychaetes–are the main source of food for demersal fishes and sea ducks, such as the velvet scoter. The sandy slopes might appear mostly unchanging, but only from the perspective of a human lifespan. The tree stumps, found in these zones within the Lithuanian coastal waters of the modern Baltic Sea, at the depths of some 27 m at Juodkrantė and 14 m at Melnragė are the proof of extensive pine forests that were once growing there about 11-9 thousand years ago. Back then, the water levels were significantly lower and the territories presently covered by the sandy slopes were part of the coastal areas.

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Baltic macoma (Macoma balthica, Linnaeus, 1758) The Baltic macoma is a small marine mollusc with an oval shell featuring distinctive growth rings. The colour of shells may range from pink or whitish to pale yellow or even orange. The colouration of this clam is known to depend on its habitat, nutrition and water currents. The shells of the offshore individuals are usually thicker and brighter, whereas those living in shallow waters tend to have bigger but thinner and paler shells. Baltic macoma lives buried in the surface layer of sediments and feeds by protruding long and adjustable siphons which could be up to 10 times longer than the length of the shells. Dependent on its habitat, Baltic macoma may use different feeding strategies. Macomas living on shallow sandy substrates filter out their food from the water column with the help of these siphons, whereas those inhabiting deeper and silty bottom areas use them to suck in small particles of decomposing organic matter from the surface of the substrate. It is the most widespread invertebrate species in the Baltic Sea. To flatfish, macoma is the key source of food. They

51

are also consumed by sea ducks foraging on benthic invertebrates, such as velvet scoter. The shells of Baltic macoma are easy to find on the beach. Since their growth rate is lower in winter and higher in summer, the shells display a pattern of growth rings which allow to determine the age of an individual. Usually macomas live for 5‑10 years.

Sand gaper (Mya arenaria, Linnaeus, 1758) The sand gaper is the first invasive species in Europe. It is thought to have been brought as early as 13th century from North America, along with the boulders used by Vikings as a ballast for their boats. Sand gaper has a very thin and fragile calcium carbonate shell which can reach up to 15 cm in length. The colour of the shell ranges from dull pink to grey. Sand gapers usually live burrowed some 15-25 cm deep into sand or sill. Because of its physiological adaptation, sand gaper can live in a broad range of temperatures ranging from -2 °C to 28 °C and tolerate very low salinity. The spawning takes place twice a year, when the molluscs release into the water millions of floating eggs which turn into larvae in about 12 hours. The larva stage lasts for 2-3 weeks, when they drift at the water surface before sinking to the bottom as tiny molluscs of some 0,2 mm. Sand gapers reach maturity between the 1st and 4th year of their life. Their life expectancy is relatively long, 10-12 years, the maximum registered age being 28 years. Because of its longevity and easy identification, this mollusc is used as a bioindicator for the assessment of environmental status in the entire region of the Baltic Sea.

Sub l i tt o r a l s a n dy s l o p e s


Sand gaper

Sand gaper feeds on microscopic plankton (diatoms, bacteria and other tiny organisms) as well as on decomposing organic matter which are captured by filtration. The molluscs burrow into the substrate and then stick out to the surface a specific tubular organ–siphon. One of its openings is used to suck water in, then, as all useful content is absorbed, the surplus water is ejected through another opening. An adult sand gaper is capable to filter over 50 l of water per day. Sand gapers are preyed upon by demersal fish and diving sea birds. The empty shells are beached by the waves, so they can be found while walking along the shore.

Lagoon cockle (Cerastoderma glaucum, Bruguière, 1789)

Cockles are typical inhabitants of the intertidal zone, but the Baltic species is adapted to permanent life on the sublittoral slopes. Its close relative, the common cockle (Cerastoderma edule), is a favourite seafood in many West European countries. Their popularity as a seafood is caused not only by their excellent taste but also by high abundance (for instance, in the North Sea the density of certain populations may reach 10 000 individuals per sq. m). As they are filter-feeders and live in proximity to human populations (for instance, in sea bays), they might pick up some pathogenic organisms, e.g. the intestinal bacterium Escherichia coli. Therefore the European Commission has set specific requirements on the treatment of these molluscs intended for human consumption. Cockles are found in the Mediterranean, Caspian, Black and North Seas. They are sensitive to chemical pollution and disappear from strongly contaminated waters.

Lagoon cockles are filter-feeders living burrowed into soft substrates in the shallows. Their larval stage encompass 11th to 30th days of their life spent in the open sea, then the young individuals produce special byssal threads to attach themselves to filamentous algae before they burrow several centimetres deep into the bottom. The spawning takes place in May-July. Lagoon cockles live for about 5 years and reach the size of 1.5 cm in the Baltic Sea. Lagoon cockles have a rounded shell with 22-28 radial ribs and, perpendicular to them, clearly visible embossed growth rings. These rings, which reflect the differences in growth rates during cold and warm seasons, can be used to determine the age of cockles. The colour of shells ranges from white, beige or yellow to dark brown. Some individuals may feature small blue spots.

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Sub l i tt o r a l s a n dy s l o p e s


Brown shrimp (Crangon crangon, Linnaeus, 1758) The brown shrimp (also known as the common shrimp or sand shrimp) is the most abundant shrimp species of sandy coastal zones, wherein their numbers in summer season might reach up to 60 individuals per sq. m. These shrimps burrow into the sand during daytime to avoid strong surf or predators and to ambush their own prey. At night, they set for active hunting. The brown shrimps are not very picky about food. They forage on algae, various larvae and molluscs. In the Baltic Sea, the species grows 3-5 cm long, while in some other seas they might even reach 9 cm. Being that big, they are capable to prey even on smaller fish. The females are relatively bigger than males. The latter mate only once in the lifetime, thereafter they change their gender and become females. The gender transformation lasts for about two months. The average life span is 2-3 years. As all other crustaceans, the brown shrimps undergo ecdysis while growing. At higher water temperatures, the process reoccurs every 8-9 days, and the shrimps gain 1-3 mm in size after each round. In summer, the females carry under their abdomens some 4 500 eggs which take 4‑13 weeks to hatch. Because of the low salinity of the Baltic Sea and seasonal temperature fluctuations, the shrimps living in the

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Lithuanian coastal waters are relatively smaller than those living in normal sea water but they are still suitable for human consumption. We might not be used to eat our shrimps because of their small size, but they are popular food source for gulls, terns and demersal fish. The brown shrimp is one of the key commercial species harvested in the North Sea. The biggest catches are landed by the Dutch and German fishermen. The curious and observant holiday makers might get a glimpse of these shrimps, while wading in the shallow sea waters.

Relict amphipod (Monoporeia affinis, Lindström, 1855) This species is a relict of the last glacial period which inhabits the soft bottom substrates of both fresh and saline water bodies. It lives at the depths of 40–60 m, where the population density might reach some 10 000-20 000 individuals per square metre. This small (8 mm) relict amphipod, formerly referred to as Pontoporeia affinis, does not have a common name in the Lithuanian language. M. affinis plays an important role in mixing bottom sediments. By digging into the substrate in search for organic material, these amphipods promote circulation and exchange of various substances between the bottom sediments and deepest water layers. Amphipods of the Monoporeia genus perform active nocturnal migrations within the water column. In other parts of the Baltic Sea, where this species occurs in more shallow waters, it also demonstrates vertical migrations following the daily cycle. In daylight, they hide in the substrate

from predators while at night they actively swim in the water column. There are references, suggesting that in some regions of the northern Baltic Sea the abundance of M. affinis follows a fluctuation pattern with 6-7 years cycle. The causes of this fluctuation are not yet understood. The species is very sensitive to hypoxia and contamination, therefore it is a perfect indicator of good water quality. Throughout its entire life cycle, which lasts 1-3 years, M. affinis breeds just once. The mating takes place in autumn, while in spring the females produce some 20-30 offspring. These amphipods fall prey to demersal fishes, such as flatfish, and the isopod crustacean Saduria entomon. The specimens of this species are not to be seen on the beach. They can only be inspected in deeper seabed samples collected by scientists. M. affinis can also be found in deep

and cold lakes of the glacial origin. Curiously, it is considered extinct from the Lithuanian inland waters and listed in the national Red Data Book under category “0”. However, in the Baltic Sea, it is a relatively common species in the appropriate habitats.

Relict isopod crustacean (Blyškusis jūrvėžys in Lithuanian) (Saduria entomon, Linnaeus, 1758) Saduria entomon is a relict of the last glacial period who migrated from the Barents Sea into the Baltic Sea more than 12.5 thousand years ago. Its distribution range has been changing over time, sometimes shrinking, sometimes expanding, but nowadays the species is spread all over the Baltic Sea. Because of successful adaptation to a broad

Relict amphipod Monoporeia affinis

55

Sub l i tt o r a l s a n dy s l o p e s


Relict isopod crustacean Saduria entomon

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THE BOOK OF THE SEA

salinity range (from 1 to 20 ‰), S. entomon is also found in Lake Ladoga and at least 8 Swedish lakes. Most likely due to external resemblance, in Lithuania it has another vernacular name that translates as the “sea cockroach” (Locally applied to a few other crustacean species in different countries. [Translator’s remark]). This species is one of the largest crustaceans of the Baltic Sea. The largest, 9 cm long specimen was found in the Gulf of Bothnia. The females usually reproduce just once in their 3-4 year lifespan, because after the spawning they tend to die of exhaustion. S. entomon does not tolerate warm water, so it retreats into the deeper areas in summer. These isopods inhabit broad range of bottom substrates: sandy plains, boulder accumulations, morainic deposits or silt sediments, wherever demersal fauna is rich. They crawl on the seabed leaving distinctive trails. If necessary, these isopods are also capable of swimming in an upside-down position, although this is not a typical behaviour. S. entomon is a predatory species, preying upon benthic animals, usually other smaller invertebrates. They are also considered as cannibals capable of feeding on their own species, or scavenging for any other decaying flesh. They themselves fall prey to commercially important Baltic fishes, such as cod or flatfish.

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Small sandeel (Ammodytes tobianus, Linnaeus, 1758) The small sandeel is widespread in the North Atlantic, from Murmansk down to Spain, including Iceland, the Baltic Sea, as well as the Mediterranean Sea. At the Lithuanian coasts, they are common in sandy shallows and rarely seen in the offshore waters. Sandeels usually swim in shoals, sometimes very close to the shoreline. They spend significant share of time burrowed in the sand. In winter they are inactive and hide in the sand, burrowing up to 20-50 cm deep. Sandeels feed on zooplankton, crustaceans, worms, sometimes also on juvenile fish. They themselves fall prey to bigger predatory fishes, such as cods, turbots, eels, occasionally even flounders, and the juvenile small sandeels are also eaten by the Baltic herrings and great sandeels. Quite many sandeels are captured by fish-feeding sea birds. The small sandeel is a typical fish of the Baltic coastal waters, similar to a much rarer species, the great sandeel (Hyperoplus lanceolatus). The body of this small fish reaching 10-15 cm (max. 25 cm) is elongated and covered in tiny scales. The dorsal fin is very long, the anal fin is shorter by half, the pectoral fins are small, and the pelvic fins are absent altogether. The dorsal part is greenish-blue,

Sub l i tt o r a l s a n dy s l o p e s


the sides bear a shade of yellow, while the belly is silvery. The lower jaw does not have large teeth and is protruding forward, the mouth is wide. When this fish opens its mouth, the latter folds out like bellows. The lifespan reaches 10 years. Small sandeels reach sexual maturity at the age of 1-2 years and spawn in summer or late autumn in the coastal waters up to 30 m deep. The females produce 4‑22 thousand eggs with the diameter of 0.8‑1.0 mm, released in small clusters onto the sandy bottom. The larvae are 4‑8 mm long and swim in the water column until they turn into fry upon reaching 20 mm in size. Sandeels are used by humans as a bait for fishing larger species (cods, eels, turbots, flounders, etc.) as well as for the production of fish protein powder.

Turbot (Scophthalmus maximus, Linnaeus, 1758) The turbot is a typical marine fish species widespread in the north-eastern parts of the Atlantic: in the Mediterranean Sea and along the European coastline all the way up to the Polar Circle, including the Baltic Sea. Turbots prefer sandy, rocky or mixed-type bottoms and they easily tolerate the low salinity of the Baltic waters. Adult turbots prey on other demersal fish, such as sandeels, gobies, or Baltic herrings, less often they also include in their ration crustaceans and bivalve molluscs. The hatchlings, like those of other fish species, start feeding on zooplankton, eventually switching to benthic invertebrates. Because of their body shape, turbots are difficult to capture for other predatory fish or fish-feeding birds, however,

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floating larvae enable turbots to disperse far away from the original spawning grounds. Turbot is one of the most valuable commercial fish species living in the Baltic coastal zone. There is some evidence that seaside dwellers in the current Lithuanian territory were already using turbots for food as early as 3 000 B.C. Turbot is a slow growing fish, often subject to over-exploitation due to the high demand, therefore the stocks are declining in many areas. The most popular fishing method is by nets in the coastal waters before the spawning. This valuable fish may be cooked in many different ways; turbots can be grilled or stewed spiced up with different seafood, mushrooms, wine, vermouth or champagne. young turbots sometimes fall prey to cods while the adults may serve lunch to seals. Turbot is a flat, almost round-shaped fish. The “dorsal” side of the body where both eyes are situated is not covered in scales but features harsh osseous bumps. Turbots are capable to adapt the colour and pattern of their upper side to the background, which makes these masters of camouflage difficult to spot to both humans and their prey–other fish. The downward facing side is usually white, although sometimes it bears pigmentation spots. The mouth of this typical predator is very wide, adapted to swallowing rather big prey. Turbots may reach 25 kg, although in Lithuanian waters they are significantly smaller, usually under 1 kg, and only exceptional specimens weigh 7 kg. Turbots normally live away from the shores, but in spring they arrive to the coastal shallows well before the actual spawning. The spawning happens in batches in MayJune, the overall fecundity may range from 0.5 million to full 14 million tiny floating eggs. These eggs and the hatched

European flounder (Platichthys flesus, Linnaeus, 1758) The European flounder lives along the north-eastern Atlantic coastline, from the White, Barents and Baltic Seas down to the Mediterranean and Black Seas. This species tolerates

59

different salinity levels and is abundant at the Lithuanian coast, often entering also freshwater bodies, such as the Curonian Lagoon or some river estuaries in other countries, where they may migrate significant distances upstream in search for food. They are most common on sandy bottoms, up to 50-60 m deep. The juvenile fish usually stick near the shore, while the big adults retreat into the deeper areas. The young feed on zooplankton, insect larvae, or small crustaceans, later switching to molluscs, worms, shrimps and fish or their young as they grow bigger. Adult flounders are a difficult catch for other predatory fish, such as cod, because of their body shape, so mostly juvenile flounders fall prey to them. Smaller founders are sometimes grabbed by cormorants, while the big ones are hunted by seals. The body of the European flounder is asymmetric, oval-shaped, flat on the sides. The lateral line is surrounded by little spikes, situated at the anal part and the basis of the dorsal fin–this is an important identifier, enabling to distinguish it from another similar species, the European plaice (Pleuronectes platessa), which is rare in our waters and does not have such spikes. The upward facing side is brown or khaki coloured with brown or orange spots, so it blends well with the colours of the substrate. This enables flounders to camouflage well and avoid detection. The downward side is white, sometimes with spots. The mouth is small, with small teeth. In the Baltic Sea, flounders can reach 45 cm and 1.2 kg, although the usual size is 20-30 cm. European flounders reach sexual maturity at the age of 3-4 years, and they spawn in March-May in the coastal waters or deeper water areas. There are opinions that two varieties of

Sub l i tt o r a l s a n dy s l o p e s


flounder exist and they even show some genetic differences: the eggs of flounders spawning near the coast sink to the bottom, while those of the specimens spawning in the deep zones are buoyant, i.e. they float in the water column. The fertility is 0.4‑2 million eggs. The hatchlings have their eyes on both sides, but as they grow, they undergo metamorphosis and their eyes move onto one side–the juveniles are about 10 mm long by that time. Archaeological data suggest that flounders were used for food by the coastal dwellers as early as 6 000 B.C. in the current German territory, some 5 thousand years ago in Estonia and some 3 thousand years ago in Lithuania. Nowadays flounders are important part of the commercial fishing in the Baltic Sea, usually fished by trawls or other nets. In Lithuania they are usually fried, sometimes smoked, and their fillet can be used by experienced chefs in variety of dishes to please even the most demanding taste.

Velvet scoter (Melanitta fusca, Linnaeus, 1758)

of the velvet scoter. Within the last two decades, however, the wintering stocks of this species have declined by about 60 %, the latest counts suggesting some 370 000 birds. The main threats possibly responsible for such dramatic decline are oil pollution, accidental catches by various fishing gear and eutrophication. The global warming could have caused a certain shift of the wintering grounds, however, this possibility has not been properly explored yet. The species was included into the IUCN Red List of Threatened Species in 2012. Abundant aggregations of scoters in the Baltic Sea are observed in Pomeranian Bay, the Irbe Strait, the Gulf of Riga and along the Lithuanian and Latvian coastlines. The largest aggregations in Lithuania are observed in front of the Curonian Spit where sandy seabed is prevailing. Individual birds can be seen in the inland water bodies. When in the sea, velvet scoters are found not only in the shallow coastal waters but also offshore, in much deeper areas reaching up to 30 m. In the last few years, new big offshore aggregations of almost 30 000 individuals were also observed in the area of Klaipėda–Ventspils Plateau in front of the Lithuanian coast. As many other diving sea ducks, velvet scoters are benthic feeders–they forage on molluscs and other invertebrates, often digging them out of the soft substrate.

Velvet scoter

Common scoter

This is a northern bird species. It breads in the inland waters of taiga and forest tundra as well as at the coasts of the Arctic seas. The breeding range includes also some Baltic coastal states: Estonia, Sweden, Finland and Russia. The wintering grounds are in somewhat more southern seas: the North, Baltic and Norwegian Seas. The wintering birds ringed in Common scoter Lithuanian waters were registered breeding in the northern (Melanitta nigra, Linnaeus, 1758) part of Russia, from the Arkhangelsk administrative district in the west to the Taimyr Peninsula in the east. At the first sight this sea duck is very similar to the velvet Some 20 years ago, the wintering grounds in the Baltic scoter. The main difference from the latter is the absence of Sea used to attract about 93 % of the regional population a white speculum on their wings in both male and female

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THE BOOK OF THE SEA

61

Sub l i tt o r a l s a n dy s l o p e s


common scoters. This identifier, however, is only seen when This species can be seen both at the Curonian Lagoon coast the birds take flight. and near Palanga. The flocks are usually denser that those As many other sea ducks, the common scoter is a north- of the velvet scoter. Their favourite wintering grounds are ern species wintering in more southern seas. Contrary to the shallow coastal waters with the depths not exceeding 15 m. long-tailed duck and the velvet scoter, the common scoter Separate individuals can be noticed in the inland waters. can breed further away from freshwater bodies, wherever it Their main food are molluscs but other invertebrates are finds a suitable shelter to hide the nest (under some tundra also eagerly picked up. shrubs, in tall grass, etc.). Within the last 20 years, the Baltic wintering stocks The largest wintering aggregations in the Baltic Sea are of the common scoter have declined almost by half. This registered in the western part of the sea, in Polish, German decline is explained by certain breeding failures in their and Danish waters; Kattegat attracts especially numerous northern breeding grounds, as well as by risks at the winterflocks. In Lithuanian waters, the wintering population is ing areas: accidental catches by fishing gear, oil pollution and sparse, with just a few hundred individuals registered annually. eutrophication.

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Reefs

It may sound incredible, but reefs do exist in the Baltic Sea! They might be less colourful that the famous coral reefs, but that does not make them less interesting or valuable. It takes more than just diving into the sea to discover the treasures and bright colours of these reefs–you would need some good luck. You have to wait for the clear offshore water and a bright sunny day. And then it would be entirely up to you to find the right spots where the reef reveals its secrets...

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Reefs


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65

Reefs


A

I K

C D

B

J L

G N

F

H

E

M

A

Long-tailed duck

H

Round goby

B C

Steller’s eider

I

Spawning Baltic herring

Great crested grebe

J

Baltic herring eggs on black carrageen

D

European eel

K

Black carrageen meadows

E

Lumpfish

L

Baltic isopod

F

Shorthorn sculpin

M Mussels

G

Eelpout

N

Bay barnacle

Boulders at the Lithuanian coast, at the depth of 8 m

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THE BOOK OF THE SEA

67

Reefs are submerged oases supporting huge variety of bottom animal and plant species. The hard substrate offers excellent conditions for seaweeds to attach, while a complex bottom structure provides numerous hideouts and shelters for animals to hide. Seaweeds attract highly diverse animals who use algae as a food source, breeding grounds or hiding places. Although in other seas the prevailing reefs are of biological origin, built by the coral polyps or soft corals, the basis of the Baltic reefs is made of rocks or boulders. In Lithuanian waters, the boulder-based reefs are most common. In shallow waters up to 15 m deep, where light still reaches the bottom, the boulders are usually covered in vegetation. At some locations, the bottom relief creates areas sheltered from waves, therefore bottom seaweeds become so dense that they leave no space for benthic animals to attach to the boulders. Such thickets, especially those made of the black carrageen, a perennial red seaweed, are important spawning grounds of the Baltic herring. The eggs laid on the thalli of red seaweeds are thought to have especially favourable development conditions, while the fry finds a lot of hideouts from the swell and predators. Reefs can vary greatly according to their form and benthic communities evolved on their basis. Quite recently, merely a decade ago, unusual underwater ridges were discovered near Palanga; they reach 5 m in height, are narrow and stretch for a few tens of metres, with their slopes steep like walls. These ridges consist of especially hard type of clay, covered in mussels and hydroids, and they are usually found in clusters at the depths of 15-17 m. The ridges are thought to have formed more than 130 000 years ago. These unique structures were noticed when modern multibeam echosounders were applied in depth measurements. Precise maps of the ridge distribution along the Lithuanian coast were produced with the help of these echosounders. Until now, similar ridges shaped by glaciers have been discovered worldwide only in the Scottish waters, and in the Baltic Sea this remains the only location of such unusual reefs. The ridges have become a favourite spot among diving enthusiasts.

Reefs


In the deeper areas, where the light is limited or the seabed conditions are less favourable for seaweed thickets to form (e.g. in the proximity of sandy fields), the key elements of the reefs are dense mussel colonies. In Lithuanian coastal waters, the density of mussels in such colonies may reach tens of thousands individuals per square metre, their weight reaching 3‑7 kg. The available data suggest that the larger the number of colony-forming molluscs, i.e., the higher the density of these colonies, the more species of other benthic animals are observed there. For example, in small colonies with the mussel densities reaching only 5 thousand individuals per square metre, on average 8 other species of benthic animals are found, whereas with the mussel densities increasing to 15 thousand individuals per square metre, the average count of other animal species increases to 12. It was also established that in these colonies the molluscs settled on the top of the reef are four times bigger than the ones on the slopes. So far there is no clear scientific explanation to this phenomenon, although some scholars think that living on the reef tops offers mussels better conditions for filter-feeding and thus facilitates their growth.

Reef distribution at the Lithuanian coastline

Šventoji

Palanga

Underwater ridges stretching into the sea away from the Palanga pier

The contour of a reef lying at the depths of 15-20 m in front of the town of Palanga Reef crests

Troughs between reef crests

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69

Reefs


Abundance of long-tailed ducks based on visual counts from

Numbers of round gobies caught in Lithuanian territorial

Black carrageen

the shore (in thousands of individuals)

waters by monitoring nets (number of specimens)

(Furcellaria lumbricalis (Hudson), J.V.Lamouroux, 1813)

3500 1392 671 107

72

80

18 1262

1438

1354

2

886 537 2006 2007 2008 2009 2010 2011

434 2012

2006 2007 2008 2009 2010 2011

2012

Since the invasion of the round goby into Lithuanian waters in 2002, the numbers of mussels have significantly declined, leading to the changes of coastal reefs. In the places where the boulders used to be covered in dense colonies of these bivalves, nowadays the bay barnacle prevails. Large mussels are found only on the topmost parts of the boulders; they are too large for gobies to swallow, and swimming up to the top also requires much more effort. As mussels declined, velvet scoters also abandoned these sites where they used to forage throughout winter. Contrary to the coastal reefs, the offshore reefs retained abundant mussel colonies. This makes them especially valuable feeding grounds for demersal fish, first of all flatfish and cods, as well as for wintering waterfowl, such as long-tailed ducks. For instance, the reefs of Klaipėda–Ventspils Plateau located near the Latvian border at the depths of 24-40 m remain very important for both fish and birds. The concentration of long-tailed ducks over the reef is 5 times higher than in the surrounding waters, while the density of cods and flatfish among the boulders of the reef is 2-3 times higher than in the deeper areas.

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JŪ T H ROS E B O KONK YOG FA T H E S E A

In the Lithuanian coastal waters between Palanga and Šventoji, the black carrageen forms extensive zones of dense meadows attached to different substrates of the underwater slope, such as gravel, cobble or boulders. The black carrageen can itself serve as a substrate to other prevailing fauna and flora species, therefore the boulder fields with Furcellaria lumbricalis meadows are distinguished as one of the Lithuanian coastal biotopes. This biotope is favourable to other species of aquatic vegetation, while the majority of fauna consists of mussels and barnacles. The meadows of Furcellaria lumbricalis are the main spawning grounds of the Baltic herrings which reproduce in spring. The fry finds shelter from predators in their tangles and also plenty of food. Reef habitats based on the black carrageen meadows

have the greatest biodiversity in the central part of the Baltic Sea. During the spawning of the Baltic herring in April-May, their eggs deposited on the carrageen thalli attract numerous other fish and sea birds. Annual growth rate of Furcellaria lumbricalis is about 1 cm, ant the thalli may reach up to 30 cm. During the growth, its laminae branch into two (this is called dichotomous branching), which means that this seaweed does not have a single well expressed stipe. Black carrageen contains some anti-bacterial, fungicidal and phytotoxic substances. One of them is histamine. This substance is involved in all development stages of the seaweed providing defence against grazing animal species.

Green branched weed (Cladophora sp., Kützing, 1843) Cladophora is a genus of green algae found in shallow lakes, rivers and seas, attached to boulders or submerged wooden constructions. Some 300 species of this genus are known worldwide, but only 2 species are common in the Baltic Sea: Cladophora glomerata and Cladophora rupestris. Green branched weeds produce dense, tangled, branching, segmented strands of up to 13 cm long. Cladophora species are found at the depths of up to 10 m. The fastest growth rate is registered in May-June, so by July, they may cover entire surfaces of certain boulders. Cladophora cannot firmly attach to the substrates, therefore they are sensitive to waves, which can tear them away and carry floating in the water column or wash ashore where they decompose. Cladophora are capable of both sexual and asexual reproduction.

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Reefs


The algae of the Cladophora genus are used in aquariums, where their tangles produce oxygen and purify water. In some Asian countries certain Cladophora species are also known under the name “Mekong weed” and are consumed for food in fresh or dried form. In the Baltic Sea, green branched weeds are eaten by some invertebrates.

Bay barnacle

as early as 19th century attached to boats or in the ballast water. The first discovery of Amphibalanus improvisus was registered there in 1844 near the current town of Kaliningrad. Nowadays bay barnacles are found in all parts of the Baltic Sea. Being able to adapt to changing temperatures and salinity levels, capable to survive in low-oxygen environments, under intense eutrophication and chemical pollution, barnacles are found at almost any coastline world-wide. Amphibalanus improvisus forms a white or yellow coneshaped shell consisting of lime plates, which is usually 1 cm tall and 1-2 cm wide. The abdomen is rudimentary and the thorax bears six pairs of dichotomous filtering limbs. As the upper plates are opened, bay barnacle protrudes these limbs outside to produce a fan-like structure. By periodically unfolding and retracting that fan, barnacles filter out from the water tiny organic particles, other small animals and phytoplankton cells, which all comprise their diet. Amphibalanus improvisus is a hermaphrodite (an organism producing both male and female sex cells), however, cross-fertilisation is obligatory. From the fertilised eggs hatch

floating larvae that are carried away by currents as plankton. After a certain growth period which may last up to six moths, they stop their floating journey and attach to a hard substrate transforming into adult barnacles. Their life span is 1‑2 years. Barnacles live upside down, because they attach to various hard surfaces by their head parts. The suitable substrates include coastal rocks, shells of molluscs and turtles, hard skin of whales, crabs, underwater constructions and ship hulls. In order to protect ship hulls from damage that could be caused by barnacle overgrowth, they are painted with special toxic paints damaging the entire aquatic ecosystem. The alternative, environmentally friendly protection method– mechanical cleaning by lifting ships out of water–is much more expensive. In addition to the shipping industry, barnacles cause damage to underwater pipelines and other constructions, and a lot of money is being spent to clean them from these crustaceans. The only predator of bay barnacle in our waters is the round goby.

Mussels (Mytilus sp., Linnaeus, 1758)

(Amphibalanus improvisus, Darwin, 1854) Barnacles comprise some 1 200 species world-wide, but only one of them lives in the Baltic Sea–Amphibalanus improvisus. Despite their appearance, bay barnacles are crustaceans and not molluscs. Their “cousins” are such familiar creatures as crabs and lobsters. Barnacles are considered to be among the most sedentary marine organisms, however, the bay barnacle has arrived into the Baltic Sea from North American coasts

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For a long time, scientists had been thinking that only one species, the blue mussel (Mytilus edulis, Linnaeus, 1758), had lived in Lithuanian coastal waters, but the recent genetic analysis revealed that along with Mytilus edulis, the more northern species Mytilus trossulus, as well as hybrids of both species were present. Mussel colonies, wherein their weight may reach 8–10 kg per square metre, provide exceptional hiding, feeding and attachment conditions for other benthic animals,

73

Reefs

therefore their numbers in such colonies are several times higher than those on plain boulders not covered by mussels. Mussels have been cultivated in Europe for 800 years already and consumed by humans for over 20 thousand years. Some of the ancient coastal settlements were discovered by archaeologists because of the remains of mussel shells left by the local dwellers. Although in “typical” seas mussels reach 11 cm, in the central part of the Baltic Sea they do not exceed 3.5 cm, presumably because of the low water salinity (7–8 ‰). Low salinity also restricts the lifespan of mussels in the Baltic Sea. There it lasts 12‑14 years, while in the more salty seas, some specimens may reach up to 24 years of age. Mussels feed by filtering water and capturing organic particles in their gills. To survive, some larger individuals might filter up to 65 l of water per day–those attempting to keep them in aquariums should ensure good circulation and the largest possible volume of water.


Mussels of the Baltic Sea lead different lifestyles: in the southern parts of the sea they live on sandy substrates, producing entire colonies at the sites where they find anything to attach to. At the Lithuanian coasts, in the central Baltic Sea, mussels live exclusively on boulders and other hard substrates attached by the so-called byssus strands. These strands are based on the protein collagen, which also adds elasticity to our skin. Byssus strands are both strong and very elastic. Scientists are working to create a natural glue based on their chemical composition that could be applied in ocular surgery.

A mussel colony

Rockpool prawn (Palaemon elegans, Rathke, 1837) The rockpool prawn is a species of the European coastal waters of the Atlantic Ocean, North and Mediterranean Seas, which spread into the Baltic Sea in the 20th century. How exactly this prawn became widespread in our sea is not completely clear, but in some other territories of the former Soviet Union it was introduced intentionally. The species is used for food in the Black Sea area. In Lithuanian coastal waters, Palaemon elegans is most often found near the Palanga pier, Klaipėda mole and at Karklė. The rockpool prawn does not burrow into sand,

therefore it prefers boulder fields with rich benthic flora where it can find shelter. Rockpool prawns can reach more than 6.3 cm, their transparent carapace is covered in orange or yellow spots and dark brown stripes, while the front legs and and abdomen feature blue and yellow stripes. The colour intensity depends on the living environment, the specimens living in murky waters are much paler or might lack colouration altogether. During the warm season the female rockpool prawns carry some 400‑500 eggs on their legs and breed twice a year. The spawning is triggered by sufficiently warm water temperatures. The development of eggs is determined by photoperiod–changing duration of daylight. Planktonic larvae called zoeas, that hatch from these eggs, spend all summer drifting in the water column. By autumn, juvenile prawns descend to the bottom to continue their life as adults. Palaemon elegans is preyed upon by many species of birds, seals and predatory fish. The ever spreading Baltic population of Palaemon elegans raises great concern about possible displacement of the local species, the brown shrimp, from its distribution range. So far, there is no scientific information on the ways these two species compete.

Baltic isopod (Idotea balthica, Pallas, 1772) This isopod species is a cosmopolitan widespread in Europe along the entire Norwegian coastline, in the Mediterranean and Black Seas, and even at the Atlantic coasts. In other seas, Idotea balthica is mostly found in the intertidal zone, while at the Lithuanian coasts it inhabits shallow parts of the underwater slope with abundant bottom vegetation on which it feeds.

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75

Reefs


although identification of sex is possible only after they reach lengths of 6‑7 mm. These creatures can sometimes be found washed ashore together with the tangles of black carrageens and green branched weeds.

European eel (Anguilla anguilla, Linnaeus, 1758) Although some 30 species of the genus Idotea are known world-wide, only three of them are found in the Baltic Sea, and their appearance is very similar. All the three species arrived from the Atlantic Ocean when Baltic Ice Lake gained connection with the ocean. The males grow up to 4 cm and are larger than the females. The exoskeleton is yellow, brown or green with tiny white dots, the females are usually darker. Idotea balthica can be distinguished from other crustaceans by its flat tail plate with a tridentate posterior border, where the median process is longer and acute. Idotea balthica is an omnivorous animal, feeding on benthic micro- and filamentous algae, small invertebrates and detritus. This is the key “herbivore” of the Baltic Sea, although it does not ignore animal food either. The isopod is a very important component of the aquatic communities because it supports fish diversity, serving food to some 23 species. Isopods are among the most popular invertebrates used in scientific research. This popularity is due to the fact that their generations change in about half a year, and they do not require any special care or conditions. What is rather unusual among benthic invertebrates is that the females produce young which already resemble adult specimens,

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THE BOOK OF THE SEA

European eels are distributed in Europe, North Africa and part of Asia where they live in coastal waters, estuaries, lakes and rivers. Eel’s body is long, thin, rounded and looks somewhat snake-like. The upper side is usually dark green, the lower–yellowish, however, the colours change as the fish matures, the dorsal side becoming dark blue or almost black, while the abdominal–silvery. Although eel’s mouth is not very wide, it is full of small teeth designed to hold the prey. The European eel is one of the most mysterious fishes, and for many centuries even scientists around the world did not know where they reproduced and how they appeared in our water bodies. Aristotle had been thinking that eels were emerging from mud, later this theory was replaced by another, stipulating that eelpout was the mother of eels. This theory must have inspired the German vernacular name of eelpout, Aalmutter, which literally means “the mother of eels”. Nowadays the species has been much better studied, and yet many questions about biology and ecology of eels remain unanswered. The seaside dwellers of the Baltic Sea were familiar with eels very long ago–according to archaeological data, the inhabitants of the coastal areas used to fish and eat eels at around 6 000 B.C. European eels are among the most

valuable commercial fishes. Unfortunately, their stocks are being rapidly depleted–within the last 30 years, the stock recovery rates have declined by up to 100 times. In Lithuania, most eels are caught by fish traps in the Curonian Lagoon and in smaller rivers during migration. This fish is an important object of recreational fishing, however, catching an eel with a fishing rod is quite a challenge. In Lithuania, eels are served smoked or marinated, or used to cook a tasty fish soup. The life cycle of European eel starts and ends far away from Lithuanian shores. Although nobody has ever observed eels spawning in natural environment, based on the smallest size of captured larvae the conclusion was made that their spawning grounds must be in the Sargasso Sea. The hatched larvae migrate with the Gulf Stream towards European shores where they undergo metamorphosis and turn into transparent little fishes devoid of pigmentation but already resembling an adult eel. Upon getting pigmentation, young eels settle in various coastal waters or migrate upstream into freshwater bodies. As they reach maturity, the grown-up eels start the last journey of their lives back to the Sargasso Sea where they are thought to spawn once in their lifetime and to die afterwards.

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Reefs

Eel is a predatory demersal fish. They usually spent the day hiding passively, for instance among aquatic vegetation, stones or burrowed into a soft substrate, while at night they leave their hideouts for active hunting. Adult eels forage on fish, frogs, crustaceans, and large insect larvae. The juveniles feed on small larvae and various worms that they find on the bottom. Mature eels migrating to their spawning grounds cease foraging. Their intestines are thought to undergo complete resorption during migration.

Atlantic cod (Gadus morhua, Linnaeus, 1758) A cod is a desirable catch of any recreational fisherman. According to the official data, the largest cod caught in Lithuania weighed full 19 kg! Moreover, in Norway which is further to the north than Lithuania and is notorious for its record-breaking fish, the largest captured cod weighted over 47 kg and was registered as an absolute world record– the largest cod caught by recreational fishing gear. Nowadays the Atlantic cod is a very important commercial fish of the Baltic Sea, and its stocks are strongly affected by intense commercial fishing. Although lately cod stocks have been gradually recovering, the status of the species is still classified as vulnerable. The main method of commercial cod fishing is offshore bottom trawling. Fishermen who fish in the coastal waters mostly catch cods by using gill nets. Another fishing method popular in the past, by longlines, is seldom used nowadays. As for the receipts of cod preparation, there are very many of them. It is worth noting that salted or dried cods used to be one of the key


provisions during long sea voyages, when the European seamen sailed to discover distant lands. The success of cod reproduction highly depends on water salinity. At least 10 ‰ salinity and sufficient oxygen levels are necessary for normal development of cod eggs, therefore they spawn at deeper depressions, sometimes up to 100 m. below the surface. Cod fecundity is known to depend on their size, and the biggest females were reported to produce up to 4 million eggs. The Atlantic cod is one of the main predators of the Baltic Sea mainly feeding on other fish, such as Baltic herrings and sprats, and they also demonstrate some cannibalism when larger cods prey upon their smaller kin. Large crustaceans, such as Saduria entomon, also supplement their diet. This species actively hunt for their prey in the demersal and pelagic zones of the water column. Juvenile cods feed on various crustaceans and worms. The body of cod is spindle-shaped, with a large head. The mouth is extremely large and equipped with great

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numbers of small sharp teeth. The lower jaw has a long barbel. The body is greenish with the shade of grey or brow and mottled with brown spots. Cods are widespread in the North Atlantic and Arctic waters. Beyond doubt, this is one of the most important marine fish species of the Baltic Sea where it is adapted to the low salinity conditions.

Three-spined stickleback (Gasterosteus aculeatus, Linnaeus, 1758) An outstanding feature of this species is three spines at the dorsal fin providing defence against predators as well as bony plates on the flanks producing a sharp edge. The dorsal part is greyish-green, the sides are yellow or silvery. Before spawning, the males turn red and the females develop dark spots on their sides. The males demonstrate interesting behaviour: they build nests on the bottom, using plant material and their mucus,

then use a special “dance” to attract females to them and guard the eggs laid in the nest till they hatch. Their lifespan is 3‑4 years and the maximum body length reaches 11 cm. The three-spined sticklebacks inhabit both salty and fresh water bodies: seas, estuaries and lakes. They are widespread in the Northern Hemisphere, from the temperate zone in Europe to the Black Sea, North Africa, but also in North America, Greenland and East Asia. Sticklebacks feed on crustaceans, insect larvae and eggs of other fish. They are abundant in the Baltic Sea; at certain locations, where they gather into shoals, they might even eliminate zooplankton and thus provoke algal blooms. Sticklebacks use to be fished and used as fodder for ducks, pigs, farmed fur-bearing animals or other fish, and also used in fish oil production. Although never considered a valuable commercial fish, the three-spined stickleback has become a true “superstar” of laboratories due to its morphological diversity, unique behaviour and short life-cycle, which make it an irreplaceable test animal in evolutionary biology or behavioural studies, the numbers or studies being comparable to those done on mice or Drosophila fruit flies. From their feeding grounds in the Baltic Sea, sticklebacks migrate for spawning to the coastal waters including the Curonian Lagoon. The eggs are released in batches in May-July, when the water warms up to 18‑20 °C.

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Shorthorn sculpin (Myoxocephalus scorpius, Linnaeus, 1758) The shorthorn sculpin is a fish of impressive appearance widespread in all seas of Northern Europe. The fish is up to 30 cm long, very spiky, usually dark in colour with a bright orange or red belly mottled with white spots. The head is enormously big, with a broad forehead, equipped with large spines. The eyes and the mouth are also very large. The mouth is full of small teeth designed to grab and hold the prey. Sculpin is a typical demersal predator, ambushing its prey from different hideouts at the bottom. Its diet consists predominantly of other juvenile fish (cod, flatfish, European smelt, Baltic herring, etc.) as well as of small adult fish (sprat and sticklebacks) and larger crustaceans. Sculpins are of no commercial value, so they are not subject to specialised fishing, however, recreational fishermen catch them quite often when using animal bates. Taken out of the water, this fish demonstrates a peculiar behaviour: it puffs up, spreads its spikes in defence and produces a buzzing sound by vibrating some muscles in the frontal part of its body. Shorthorn sculpins spawn in the coldest season–in December‑February. The females, who are normally slightly larger than the males, produce up to 2 700 red sticky eggs, which clump into clusters and stick to seaweeds. The males protect and defend these eggs. These fishes are usually found in the coastal waters up to 25 m deep although sometimes they are caught also at greater depths. They are sedentary but demonstrate some seasonal relocations, moving close to the shore in summer and deeper


in winter. Sculpins occupy different habitats, both on sandy and rocky bottoms, while temperature or salinity changes have little effect on their spacial distribution.

Lumpfish (Cyclopterus lumpus, Linnaeus, 1758) The lumpfish, whose vernacular Lithuanian name translates as “the sea toad”, is an odd-looking Baltic fish, growing up to 5.5 kg, although in Lithuanian waters much smaller individuals under 200 g are caught only occasionally. The natural distribution range of this species covers the northern part of the Atlantic, the North and Baltic Seas. Lumpfish is a relict of the last glacial period (12 000 year ago) in the Baltic Sea. The diet of this demersal fish mostly consists of crustaceans, bristle worms, fish larvae and small fish. The most active foraging period is in winter, while during the spawning it ceases feeding altogether. The body of lumpfish is short, almost spherical and devoid of scales. The upper side is dark, greenish or grey, while the lower side is usually pale yellow. The mouth is small, adapted to small-sized prey. The pelvic fins have evolved into suction discs which it uses to attach to boulders.

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The lumpfish spends most of its life far away from the shores, in the open sea up to 200 m deep, hiding among boulders and rocks on the seabed and approaching the shores only during its reproductive migrations. Several catches of lumpfish have been registered even in the northern part of the Curonian Lagoon during the spawning period. The spawning of lumpfish is extended in time and lasts from February till May. The eggs are released in batches on hard stony substrate or in the thickets of seaweeds (such as kelp). The females leave the eggs after spawning and retreat from the shores, while the males stay to take care of the eggs, which they fan with their pectoral fins. The hatchlings are also supervised by the male for some time, and only later, as they gain in size, they start independent life. In Lithuania, this fish has no commercial value and is not subject to targeted fishing or used for food, however in Iceland and Denmark, it is consumed salted, dried or smoked.

Eelpout (Zoarces viviparus, Linnaeus, 1758) The eelpout (also known as viviparous blenny/eelpout) belongs to the marine fish family Zoarcidae. From appearance, it resembles an eel, however, the elongated body is usually light yellowish with a pattern of dark spots. The eelpout body is slimy, its small scale are sunk into the skin, leaving the impression that the fish is scaleless. The largest specimens reach 50 cm in length and 500 g in weight. They are found in the coastal waters of the seas of Northern and Eastern Europe. Among the Baltic fish, it is a true relict of the last glaciation.

Lumpfish

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This fish is peculiar because of its bones which are greenish in colour due to the pigment vivianite. The green skeleton may appear a bit weird, however, the flesh is perfectly edible. The young of eelpout have a great similarity to the glass eels, therefore for long years, before the true breeding biology of the European eel was discovered, the eelpout was broadly believed to give birth to eels. The eelpout fully justifies its vernacular names–contrary to most other familiar fish species, it does not spawn eggs, giving birth to 30‑400 fully developed young instead. This fish is characterised by internal insemination and complete development of eggs and hatchlings in the mother’s body. The eelpout is a demersal fish usually found at depths of up to 40 m on solid stony or rocky bottoms, where it hides in cracks or among bottom vegetation. It is passive in daytime, foraging more actively at night. The main diet consists of snails, crustaceans, bottom-dwelling worms, fish fry and eggs. They themselves fall prey to many predatory fish and fish-feeding birds.

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Freshwater fish The Baltic Sea salinity is relatively low, therefore its coastal waters often contain some typical freshwater immigrants: European perch, pike-perch, roach, freshwater bream, white bream, etc. However, their abundance in the coastal waters depends on the season and hydrological conditions–these fishes are usually observed there in the warm season and calm seas. Freshwater fish are usually absent from the offshore waters of the Baltic Sea, but at the coastal waters, especially in the warm season, they constitute a significant share of commercial catches. The dominant freshwater species in those catches are the European perch, pike-perch and freshwater bream. Some freshwater species, such as perches and pike-perches, migrate from the Curonian Lagoon to the Baltic coastal waters each spring after spawning, move between brackish and freshwater zones in the summer and in autumn, when the sea water gets colder, they return to the Curonian Lagoon for wintering. This migratory behaviour is considered to be linked with better foraging conditions in the Baltic Sea and a positive impact of the brackish water on physiological processes of fish. It may also be the case, that migrations allow these fishes to get rid of some ectoparasites that do not tolerate brackish water. Freshwater fish species usually swim into Lithuanian Baltic coastal waters from the River Šventoji and the Curonian Lagoon. Most freshwater fish do not breed in saline water and start their migrations to the sea only after spawning in fresh waters. Their abundance and species composition in the marine coastal zone is directly linked with the state of

Pike-perch

Roach

Freshwater bream

European perch

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fish communities in freshwater bodies, and the latter often depends on fishing intensity and eutrophication. With the approach of autumn, in September‑October, numbers of freshwater fish at the sea coast diminish, but they are replaced by migratory anadromous fish swimming to spawn from the sea into the rivers, such as vimba bream, Atlantic salmon, sea trout and European smelt. True marine species, such as cod, Baltic herring or flounder arrive in the coastal waters in larger numbers only as the water gets cold. So in the course of a year, the coastal waters are frequently predominated by freshwater fish in the warm season, by marine species in the cold season, while in autumn they are filled with migratory fish species.

Round goby (Neogobius melanostomus, Pallas, 1814) The round goby is a species provoking heated discussions and arguments like no other fish. In the Baltic Sea, it is found in coastal waters and freshwater estuaries. The natural distribution range of round goby covers the Pontic–Caspian region (encompassing the basins of the Black, Azov and Caspian Seas), while in Lithuanian waters the first specimen was caught in 2002. The fish is relatively small, its body short and sturdy, the head is big, mouth sufficiently wide, equipped with small frontal teeth and another set of teeth deeper in its throat specialised for crushing molluscs. The body colour is adapted to its surroundings, however, the prevailing colouration is dark, almost black. The dorsal fin has a clear black spot in a yellow frame, while the ventral fins are conjoined.

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The intensive spawning of round gobies lasts from April to June in batches and in several rounds. The eggs are attached to stones, plants and other substrates. The males guard the eggs from predators and fan them with their fins. Many males die after the breeding season. The diet of round gobies is pretty diverse, however, the major part of it consists of various molluscs, crustaceans, other invertebrates and small fish. With their numbers growing steadily, gobies tend to become the main catch of the recreational fishers, fishing in the Baltic coastal zone. Their share in commercial catches is also increasing. Although this fish is not large it can be used for food–fried, smoked or canned. They are considered to be one of the most numerous fish species of the coastal waters at present, while in future their abundance is likely to decline. This is a usual population trend of all invasive species–as they occur in a new environment with no natural enemies, diseases, competitors and other regulatory factors, the population explodes, but eventually a decline follows till the population is stabilised. The round goby is considered to be an especially aggressive invader capable to produce a profound impact on the ecosystem. Spreading rapidly, round goby is likely to compete with local fish species (flounder, eelpout, etc.) for food

or habitats. It cannot be completely rejected that this small fish may even influence the abundance of marine waterfowl– the abundant populations of gobies might be consuming large quantities of molluscs which are an important food source to certain birds, thus causing a shortage of food and pushing them away into different areas. On the other hand, fish-feeding birds, such as cormorants, must be undoubtedly happy about its arrival.

Steller’s eider (Polysticta stelleri, Pallas, 1769) This is one of the rarest sea ducks. It is included in the IUCN globally threatened species list as a vulnerable species, and is also listed in the Lithuanian Red Data Book. The numbers of wintering Steller’s eiders counted at the Lithuanian coasts had been gradually increasing from 1969, when 10

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individuals were registered, till 1997, when the wintering stock reached 2 000 birds. Then, a rapid decline of the numbers of wintering eiders followed, and a decade later only 100 individuals were counted in Lithuanian waters. In the last few years only individual birds have been spotted at the Lithuanian coasts, and in some years no observations were registered altogether. The Steller’s eider is a benthic feeder, foraging on bottom molluscs and other invertebrates. At the Lithuanian coastline, it used to be very attached to their traditional wintering grounds over the mosaic cobble seabed between Karklė in the south and Kunigiškiai in the north. The wintering flocks are usually very dense, and all the birds dive in highly synchronised manner. The Lithuanian wintering grounds near Palanga used to be the southernmost aggregation of this species. Larger aggregations are registered at the Saaremaa Island in


Estonia, but even there their abundance has been declining lately. One possible explanation to this decline of the Steller’s eider in its Baltic wintering grounds is a shift in wintering locations linked with the global warming: more and more birds tend to stay for winter in the northern seas, near the Kola Peninsula and in northern parts of Norway, instead of flying to the Baltic Sea.

The water column

Long-tailed duck

In this environment, everything and everyone is in motion. What differ are the speeds and directions. Some move at will, some helplessly drift carried by waves and currents. This is the offshore realm, home to both close relatives of whales and the smallest inhabitants almost invisible to a naked eye. This is the world where no one stays in one place for too long, nonetheless, it has its own rules and order.

(Clangula hyemalis, Linnaeus, 1758) This is a northern species breeding in small tundra lakes, at the shores of the northern seas and sometimes also in larger lakes. The nest is usually built on the ground in proximity to water. Within the last two decades, the North-European/ West-Siberian population of the long-tailed duck had shrunk by almost three times–from 4.6 to 1.6 million birds. In 2012, the species was included into the list of globally threatened species. Accidental catches by fishing gear, oil pollution, eutrophication and effects of the global warming were identified as the key factors affecting their population. The Baltic Sea is a wintering ground of some 90 % of the regional population of the long-tailed duck. The birds arrive in the Baltic Sea after moulting in Northern Russia in October‑November and stay till April‑May. Merely a few years ago, they were abundant at the Lithuanian coasts near Palanga, where the wintering flocks

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used to include a few thousand, or even over ten thousand birds. However, in the last years, these wintering flocks have dramatically diminished. The most likely explanation of this rapid decline is the negative impact of an invasive species, the round goby, on the availability of mussels, the favourite food of these ducks. It is interesting to note, that the abundance of long-tailed ducks wintering in front of the Curonian Spit and foraging mostly on benthic crustaceans has changed insignificantly. According to its feeding habits, the long-tailed duck is a benthic feeder, foraging on demersal invertebrates, molluscs, sometimes also fish eggs. The diet may differ in different habitats and parts of their range. At the Lithuanian coasts, their main food near Palanga are mussels, while along the Curonian Spite–the isopod Saduria entomon.

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The water column


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The water column


Seas and oceans contain about 98 % of the total water resources on Earth. The average thickness of the global water layer is 3 680 km, and this water column is referred to as the pelagic zone (originating from the Greek word pelagos meaning “open sea”). The deepest layer of the water column on Earth is almost 11 km, while in the Baltic Sea it is way more modest–the deepest depression is the Landsort Deep but it reaches only 459 m. The average water column of the Baltic Sea is about 53 m deep. This zone is full of marine life, majority of which consists of microscopic algae or animals almost invisible to a naked eye (they are called phytoplankton and zooplankton). They constitute about half of all the diversity of living organisms in the Baltic Sea. However, this realm is also home to the largest animals, the marine mammals. Three species of seals and the only cetacean species in the Baltic Sea, the harbour porpoise, are the rulers of the pelagic zone who do not have natural enemies superior to them in their environment. Even so, they still balance on the brink of extinction because of human activities. The water column is a world where everything and everyone is in motion, because there is nothing to attach to. The only difference is that some, such as fish or marine mammals, can swim actively and reach the places they want at will, while some others have simply adapted to survive drifting with the currents or being tossed by turbulence. Despite constant water circulation in the water column, it retains distinctive layers that are important to many marine organisms. The surface layer of the Baltic Sea up to 10-20 m deep warms up in summer and does not mix with the deeper layers. It may get as warm as 16–20 °C, while the temperatures beneath reach merely 4–5 °C. This layer usually has enough light, therefore its warmer waters facilitate the most intense growth of microscopic algae. However there are animals, such as cod, that carefully avoid higher temperatures typical to this layer. The intermediary water stratum where the temperature gradient is steep is called the thermocline. This layer is below the warm surface layer and seldom exceeds 10 m. Only in calm weather with steady continental winds, which push the surface waters further offshore in the course of a few days, the cold but clear deep water rises up to the shore. Such stratification of the upper layers of the water column is common only in summer, because the autumn storms stir these strata up, and the temperatures in the water column even up till the next summer.

B A

D

C

F

Baltic grey seal

D

A school of sprats

B

Common murre

E

Opossum shrimps

C

Atlantic salmon

F

Common jellyfish

A

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THE BOOK OF THE SEA

91

Th hee wat wat er e rc ocloulmunm n


Commercial catches of the European whitefish

Commercial catches of the twaite shad

in the Curonian Lagoon (tonnes)

in the Curonian Lagoon (tonnes)

60

300

40

200

20

100

0

0 1945 1955 1965 1975 1985 1995 2005 2015

1945 1955 1965 1975 1985 1995 2005 2015

Contrary to the temperature stratification, vertical stratification of salinity is caused by the fact that the deeper, cooler and saltier water has higher density and is heavier. In the central part of the Baltic Sea bordering Lithuania, the surface water salinity of about 7 ‰ remains more or less stable down to the depths of 60 m, then within the next stratum of about 20 m it rapidly increases to 10–11 ‰, after which the salinity changes very little, no matter how deep. This steep salinity gradient, which in the southern part of the sea starts even at lower depths of some 40 m, is called the halocline. This layer is especially important to the deepwater species preferring cold water, some of which have survived since the last glaciation. This stratum is important because it creates a rather strong barrier preventing the deep water strata from mixing with the surface layer. Because of it, the oxygen content below the halocline is usually lower, and the stagnant water of the deep takes a decade to be completely refreshed. This gradual replacement is caused by the inflow of heavy and saline water from the Norths Sea, usually caused by the winds. It reaches different parts of the Baltic Sea at a different pace–the stronger the winds, the further north this water flows. In those periods the “old” water from the depths rich in different accumulated materials is pushed out into more shallow areas.

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T J ŪHROS E BO KN O YKG O AF THE SEA

Phytoplankton Phytoplankton consists of microscopic algae, and their generalised name originates from the Greek word planktos, meaning errant or drifting with the current. The largest phytoplankton organisms may reach the size of about a quarter of a millimetre, while the smallest are less than a micrometre, i.e., they measure in thousandth parts of a millimetre. These organisms are sampled by very dense nets, although the colonies of phytoplankton that dye large areas of the sea surface can be observed even from satellites. Just as the grass and the trees on the dry land, phytoplankton are the main “green” products of the sea, serving food to other organisms, first of all to small animals inhabiting the water column–zooplankton. The growth of phytoplankton depends on the available light and dissolved nutrients. On land, plants get nutrients via their root systems, but the phytoplankton cells absorb them directly from the surrounding medium. The absence of roots means that phytoplankton cells

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The water column

can be transported long distances in the water column, and since nutrients dissolved in the water are available everywhere, this “migratory” lifestyle causes them no problems leaving only one concern–to stay in the upper layers of the water column, where there is enough light. In order to get more nutrients from their environment, the cells develop to produce the largest possible surface area through which they are absorbed. When both nutrients and light are abundant, and the environment stays warm and calm, some species of phytoplankton multiply very rapidly. Their colonies dye water surface in bright colours. In the Baltic Sea, the colour usually is green–this phenomenon is called an “algal bloom”. How come that the cells of phytoplankton, which are slightly heavier than water and gradually sink, manage to stay afloat for so long? The sinking is slowed down by various adaptations, such as different projections, spikes and other forms designed to increase cell surface but not its volume, or tiny locomotive flagella and bristles, enhancing the ability to stay “suspended” in the water. Cells might also


have various “buoys“ inside–the vacuoles filled with low density liquids, and some species can connect their cells to produce chain-like colonies. Just as trees on the dry land, phytoplankton perform the process of photosynthesis and produce oxygen necessary for other aquatic organisms to breath. Phytoplankton do not need leaves, photosynthesis takes place in chloroplasts contained in their cells. Moreover, by performing photosynthesis, phytoplankton not only replenish oxygen content in the water but also reduce the amount of carbon dioxide in the atmosphere by accumulating carbon in their cells, which is eventually transferred to other organisms in the food chain as phytoplankton get consumed by them. If that does not happen, the cells eventually die and sink to the bottom, being decomposed by bacteria along the way or accumulating on the seabed as dead organic material. The latter either stays intact for long periods of time or is consumed by the benthic animals.

Zooplankton

Zooplankton Zooplankton is a collective term denoting aquatic animals that spent all or most of their lifetimes in the water column. Some of them drift with the currents and are not capable of swimming actively, while others move actively at the speeds of up to 7‑8 m per minute or 1.5 km per day, migrating deeper during the daytime to hide from predators in the darkness and resurfacing to feed at night. Zooplankton consist of either microscopic animals that are poor swimmers, or larger animals with soft body texture, such as jellyfishes. The largest of them are among the longest sea creatures reaching 40 m, but these giants do not live in the Baltic Sea. In order to see these soft-bodies animals or to collect their samples safely, the

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THE BOOK OF THE SEA

95

The water column

scientists who study them usually dive in the water column in remote offshore areas where the seabed is too deep to see. Up to 1 200 species of zooplankton have been registered in the Baltic Sea. This number does not include large numbers of small pelagic larvae of those animals whose adult forms are sessile and live on the bottom. The numbers of these larvae of bivalve molluscs and other benthic animals may reach thousands per cubic metre of water. Transported by currents, the organisms at that stage of their development are able to reach territories that adult individuals would never be able to get to. Zooplankton comprise an important part of aquatic food webs; small zooplankton usually feed on phytoplankton, while they themselves are consumed by larger forms of zooplankton or larger marine inhabitants, first of all fish. It is interesting to note that krill, which is part of zooplankton in the Antarctic waters, is the main food source of the largest marine mammals–whales. The key fish species of the Baltic Sea, the Baltic herring and the European sprat, feed exclusively on zooplankton, mostly on copepods. With the explosion of the sprat stocks, competition over food resources has increased, the trend showing growing numbers of fish with their stomachs filled with ever smaller organisms.

Opossum shrimp (Neomysis integer, Leach, 1814) No wonder that these animals resemble shrimps–they are also part of higher crustaceans (class Malacostraca) which encompasses some 25 000 species. Mysids, or opossum shrimps, are slender free-swimming transparent crustaceans of about 17 mm. Their head, eyes and thorax are shielded by


a well-developed carapace. The rostrum is acute but short. These crustaceans also have two pairs of antennae the shapes whereof are important identifiers of species. Contrary to shrimps, mysids live in swarms that are easy to spot to predatory pelagic fish during daytime. In the wild, swarming is a simple survival strategy that many organisms use, enhancing the chance of a particular individual to survive predator attacks. To avoid the attention of predators, mysid swarms descend into the darker depths during the day, while at night they return to the surface layers richer in food. In spite of that, mysids are an important food source to fish. Mysids are known as “opossum shrimps”, because they feature a brood pouch resembling the marsupium of opossums. Mysids carry their eggs in this “pocket”. An important reproductive factor is the ambient temperature which determines how many generations will be raised per year. Neomysis integer easily adapt to changing salinity levels, which allows them to spread broadly from the Baltic and North Seas down to the Mediterranean. They are also quite common in brackish bays and lagoons.

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Opossum shrimps play a very important role in marine food webs, sustaining fish stocks of commercial importance. Some studies showed that during the cold season about 80 % of the diet of cods staying at the depths of 50 m consisted of mysids.

Twaite shad (Alosa fallax, Lacepède, 1803) This is a fish of the herring family living in the Northeast Atlantic, from the southern coasts of Scandinavia to Morocco, including the British Isles and the Baltic Sea. From appearance, the twaite shad resembles the Atlantic herring, it may grow up to 60 cm and 1.5 kg. This species has a characteristic dark spot behind its gill covers and a row of 6‑10 similar spots placed along the flanks (although sometimes they are hardly visible or not visible at all). The body is covered in large thin scales. These fish tend to stay in schools and migrate long distances. They are most common in the offshore areas stretching along the sea or ocean coastline, while their juveniles are

usually found in estuaries and coastal waters, where they stay for about a year. Shads tolerate oceanic salinity, the brackish Baltic Sea water and fresh water. They swim in schools migrating in the water column in the course of a day from the surface to the demersal layers in pursue of their meals. Twaite shads feed on juvenile fish of other species (Baltic herring, sprat, etc.) and crustaceans. Twaite shads gather for spawning near estuaries and river deltas in March‑April, the males being in their 2nd or 3rd and the females in their 3rd or 4th year. As the water warms up to 10–14 °C, they rush upstream into fresh waters, usually rising just a few kilometres, however, spawning as far as 400 km upstream from the sea has also been registered. There is some evidence that in Lithuania individual shads used to swim upstream as far as the town of Prienai. Nowadays these migrations no longer happen, and the spawning takes place in the Curonian Lagoon at the Nemunas delta. Spawning proceeds near the surface in May (hence a popular local name, translating as “the Mayfish”), usually at night, when water temperature reaches 12–22 °C. While spawning, shads produce a purring noise with their tales, which must have given them their Lithuanian name “perpelė“. They produce some 12-15 (up to 230) thousand eggs which drift in the water or sink to the bottom. The larvae hatch in 2‑8 days.

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The water column

In early 20th century, the twaite shad was one of the most abundant and important fishes of the herring family in the North and Baltic Sea basins. The catches were quite significant: in 1930s, Lithuanian fishermen would land 14‑60 t annually. The stocks started to shrink in the first half of the 20th century in the entire range of their distribution. In the post-war Lithuania, the catches were steadily declining, till from the end of 1950s they were no longer registered in commercial catches. Then the twaite shad was enlisted in the Red Data Book of Lithuania. The prevailing opinion is that the negative impact on shad stocks in the entire distribution range has been produced by climate change, construction of dams, pollution and overfishing. In the middle of 1990s, the population spawning in the Curonian Lagoon unexpectedly sprang back to life and became so abundant that the species was withdrawn from the Red Data Book and even a limited commercial fishing was resumed. The twaite shad remains a protected species under the EU Habitats Directive. Lately, however, a new decline of stocks has been observed, the likely cause being overfishing. When removed from the water, twaite shads start rotting very soon, so they require a special processing and preparation for consumption. On the other hand, the fish is delicious and fat, usually consumed smoked, marinated and sometimes salted.

Baltic herring (Clupea harengus membras, Linnaeus, 1761) The herring is a typical maritime species. In the Baltic Sea, the Atlantic herring is adapted to the low salinity and is called the Baltic herring. Sometimes they even enter the Curonian Lagoon with a surge of the brackish water. In


spring, large schools of herring migrate from their wintering and foraging grounds towards the spawning areas near the coast. The feeding habits of the Baltic herring change along with their growth: the juveniles feed on small crustaceans and zooplankton in the water column, while the adult fish prefer larger bottom dwelling animals. Although herrings are a favourite food of many predators, such as predatory fish, sea birds and seals, they are well adapted and capable to escape predation: they swim in schools, blend well with the ambiance thanks to their silvery grey colouration, have acute sense of hearing and demonstrate very short reaction time to a danger. The dorsal part of herring is dark, the sides silvery and the body is compressed on the sides. The scales are small and thin. The Baltic herring is smaller than its relative the Atlantic herring, reaching the size of up to 25 cm, and in exceptional cases–up to 37.5 cm. The life span can be as long as 10 years, but in most cases it is limited to 3-6 years. Baltic herrings spawn over submarine banks, ridges and shallows covered in algal meadows in the coastal waters up to 20 m deep when the water warms up to 10 °C. Majority of the population breeds in spring, a smaller part–in autumn. A single female may produce up to 65 000 eggs. People dwelling at the coasts of the Baltic Sea used herrings for food at least since 6 000 B.C. Nowadays, the Baltic herring remains an important commercial fish. In the Baltic Sea they are fished with trawls and other nets, often in the coastal waters close to the spawning areas. Not long ago, the Baltic herring was the most numerous fish species in the Baltic Sea, however, in the last few decades their population has been shrinking and the fish appear less

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fattened, possibly because of the competition with sprats which have become very abundant. Herrings are served fresh, pickled or smoked.

European sprat (Sprattus sprattus balticus, Girgensohn, 1846) European sprats, also known as brislings (German name: Breitling, Latvian: Bretlina), live in the North-East Atlantic: in the North Sea and surrounding waters–up to the Lofoten archipelago in the North, western part of the British Isles, the Baltic Sea and down to Morocco in the South. They are also found in the northern Mediterranean and the Black Sea. These typical marine fishes are also adapted to brackish water, therefore they are very abundant in the Baltic Sea. Sprats live in large schools in the surface layers of the water column up to the depths of 5-6 m. Sprats are extremely numerous in Lithuanian waters. Both larvae and juvenile sprats, and the adults feed on zooplankton, only the size of the prey depends on the size of the fish at a particular stage of their lives. A recent study revealed that sprats also forage on eggs and hatchlings of cod, thus being able to influence the reproduction success of the latter; even more so, because they also compete with the cod larvae and juveniles for limited supplies of zooplankton. On the other hand, the cod is their main predator regulating the abundance of sprat. Sprats are also preyed upon by salmon, sea trout, sea birds and other predators. The sprat is a small fish similar to an undersized Baltic herring. They differ from the latter by their belly with a strong keel of scutes. The dorsal part is dark greenish, the sides are silvery. The scales are thin and easily shed.

Baltic herring

Sprat

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Sprats reach maturity within 1-4 years, as the body length becomes 8–12 cm. The life span is up to 6 years, the maximum size is 18 cm. The major share of sprats caught in the Baltic Sea are used to produce fodders for farmed fur-bearing animals or fish powder. Another part of the catches is used for human consumption: salted, marinated or smoked. Marinated European sprats are often sold under commercial name of “kilka” (which actually applies to the Black and Caspian Sea sprat), while smoked and canned they are sold as “sprats” (although the Lithuanian name is bretlingis). The stocks are extremely rich, although certain decline has been registered after the population peak in the middle of 1990s. Sprats spawn in the deep parts of the Baltic Sea, for instance over the Bornholm, Gdansk or Gotland depressions, especially, over the seabed slopes, usually at the depths of 50–60 m. They produce some 6 000–14 000 buoyant eggs, the larvae rise to the surface layers of the water column and the juvenile fish stays in the same areas or swim closer to coastal banks and shallows. The spawning period is prolonged, ranging between March and August, but the peak is reached in April-May, when the surface layers start to warm up faster.

European whitefish (Coregonus lavaretus, Linnaeus, 1758) This is a fish of the salmonid family widespread from West Europe to Alaska and North America. The European whitefish is easily recognisable among other fish by a small fleshy adipose fin located on the dorsal part, between the dorsal and caudal fins. The sides are silvery, the upper jaw is protruding and longer than the lower one. European whitefish live in

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many different habitats, both in freshwater bodies (lakes and rivers) and in seas. The Baltic population of whitefish spawn either in the sea (the Gulf of Bothnia) or migrate into the rivers. Our coastal waters are inhabited by the migratory form of the European whitefish, that lives in the demersal layers of the coastal waters but migrates for reproduction into the freshwater Curonian Lagoon. Whitefish feed on benthic and planktonic crustaceans as well as other invertebrates. They themselves are a favourite food not only to humans. It was established that the seals of the Baltic Sea living at the Swedish coasts mostly feed on this particular fish. Reproductive migration of mature whitefish (some individuals reach reproductive age as early as in the 5th year of their life) into the Curonian Lagoon via the Klaipėda Strait starts in September, reaching its peak in October and early November. Then in late November–early December, they concentrate at the shallow spawning grounds characterised by hard gravel substrate which are located at the western coast of the lagoon between Nida and Šarkuva, as well as at the southern coast between the settlement of Šaksvytė (Kashirskoje) and the mouth of the Deimena (Deyma) river. The spawning lasts till the freezing of the Curonian Lagoon in December. The productivity reaches 23 000‑100 000 eggs.

In the Kaliningrad district of the Russian Federation, European whitefish have been bred artificially and released in the lagoon as the fry gets bigger for several years already. The European whitefish has always been a desirable catch of local fishermen, intensively harvested by nets. Whitefishes can grow really big, up to 2-3 kg, although an individual as big as 10 kg has also been officially registered. Before the World War II, the catches of whitefish in the Curonian Lagoon averaged over 40 t per season, sometimes peaking up to 100 t. Commercial catches in 1960-70s used to reach 20-30 t, but then they shrunk to very small quantities. Presently, the status of the European whitefish stocks at the Lithuanian coastal waters is critical, and only separate individuals are caught. Such a dramatic decline of this species was caused by overfishing and, possibly, climate warming along with the negative impact of eutrophication on the spawning grounds located in the Curonian Lagoon. In spite of that, this fish does not enjoy a special protection status in Lithuania, except for a certain protection level offered under the EU Habitats Directive. European whitefish living in the sea accumulate in their muscles a lot of fat necessary for long migrations, therefore they are considered very valuable and delicious fish.

Vimba bream (Vimba vimba, Linnaeus, 1758) Vimba breams are widespread across the basins of the North, Baltic, Azov, Black and Caspian Seas. In Lithuania, a landlocked population was created after a dam was built on the Nemunas river to create the Kaunas Reservoir, and they successfully reproduce although the fish do not grow very

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big. In the sea, they usually stay in the brackish water areas close to river mouths. Vimba breams are migratory fish swimming to spawn from the sea into the rivers. In Lithuania, vimba breams inhabit the Curonian Lagoon and larger rivers, such as the Nemunas and the Neris. They tend to stay in the coastal waters, usually up to 20 m deep. The hatchlings feed on plankton and stay in the rivers till the autumn, then set off for the sea. In the sea, vimba breams forage on crustaceans, insect larvae, molluscs, shrimps, less often on aquatic vegetation. Juvenile vimba breams fall prey to predatory fish, water birds and other aquatic predators. The vimba bream belongs to the carp family (Cyprinidae). Its dorsal part is bluish-grey, the flanks and belly are silvery. The scales are large. The body is medium deep, compressed on the sides. The mouth is inferior, capable of protruding like a tube. The anal fin is very long. A distinctive edge devoid of scales stretches between the ventral and anal fins. The pectoral, ventral and anal fins are yellowish, while the dorsal and caudal fins are grey. They reach 4045 cm and 1.5 kg, very rarely up to 50 cm and 2 kg. Vimba breams grow slowly, and a ten year old fish usually weigh 750‑850 g.


The spawning takes place in May-June at the shoals and rapids of the rivers, over gravel and pebble riverbeds, as the water warms up to +13 °C or more. The males reach maturity in their 5th, the females–in the 6th year. The eggs are released in batches. A single female can produce 48‑120 thousand eggs. During the spawning, vimba breams turn dark, with their dorsal parts getting almost black, the fins gain a shade of red, and the male bodies become covered in breeding tubercles. After the spawning, the fish return to the sea. The vimba bream is a commercial fish in Lithuania. They are valuable and delicious. The best value is in autumn, when their flesh contains 12–13 % of fat. After the reproduction, the fat content shrinks to 2–4 %. Vimba breams are served fried, marinated or pickled. They are especially delicious when smoked cold or hot. Historically, in Lithuania their arrival used to be celebrated along the banks of the Nemunas river by holding a special festival called “žiobrinės“ (žiobris is the Lithuanian name of the vimba bream), at which the captured fish was cooked or smoked over bonfires.

European smelt (Osmerus eperlanus, Linnaeus, 1758) Juvenile European smelt feed on zooplankton, but as they grow they target ever larger prey–various crustaceans, including shrimps and small fish, for instance, juvenile sprat, Baltic herring or cod. Smelts themselves are desirable prey to many fish: they are hunted by eels, pikes, perches, pike-perches, eelpouts, and even some cyprinides would not miss an opportunity to feast on juvenile smelts. Smelts are often captured also by cormorants and other fish feeding water birds.

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up to 30 cm or even longer. Their distinctive features are an intense smell which resembles of cucumbers and a small adipose fin typical to their relatives, the salmonide fish. The European smelt lives in seas, estuaries and deep lakes, its distribution range covering the North Atlantic starting south of the White Sea and down to the western coasts of France, including the Baltic Sea. People have been fishing smelts since long ago, for instance some written sources of the 15th century mention smelts as one of the most important fish species used for food in the eastern part of the Baltic Sea. Nowadays these fish, especially popular among Lithuanians, are consumed fried, marinated, dried, smoked or prepared in other ways, and they also serve as a popular bait for fishing predatory species. The stocks are strong, although in some areas of the Baltic Sea they diminish due to pollution, obstructions on the migration routes to the spawning areas, destruction of the spawning grounds, overfishing, and possibly also due to climate change. The European smelts living in the Baltic Sea start spawning in early spring, some of them right in the coastal waters, but most travel in huge shoals into freshwater areas in river deltas or higher upstream. Dependent on the water temperature, the spawning takes place in February-April, over a sandy or gravel substrate. The females produce 8 00050 000 yellow eggs that stick to the substrate. The larvae hatch in 3‑5 weeks and drift downstream into the estuaries. Smelts are pelagic fish therefore their body colour is typical to pelagic species with the light lower parts and silvery-grey dorsal side. Such colouration helps to camouflage against predators. The mouths are equipped with many sharp teeth adapted to grasp the prey. Smelts grow

Atlantic salmon (Salmo salar, Linnaeus, 1758) The salmon is widespread in the temperate to polar latitudes of the Northern hemisphere. In the West Atlantic, salmon are found from West Greenland to Quebec in Canada and the Connecticut coast of the United States. In the East Atlantic, they live from the White and Barents Seas down to Portugal, including the basins of the North and Baltic Seas as well as Iceland. In Karelia and Sweden, salmon can also be found in freshwater lakes. In the Baltic Sea, Atlantic salmons live in the pelagic zone where they chase their prey, while

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with the start of the breeding migration (usually at the end of summer and in autumn) they approach the shores and migrate into the freshwater bodies to spawn. Juvenile salmon are preyed upon by many predatory fish, fish-feeding water birds (such as cormorants) and such aquatic predators as otters. Adult salmon are too large for many predators, however, for seals in the sea they are a true delicacy. Juvenile salmon in rivers forage on various invertebrates, such as aquatic insects, molluscs, and crustaceans, and on other fish, while in the sea their diet consists of crustaceans, sandeels, sprat, Baltic herring and other fish. The salmon, which is considered a royal marine fish, has a fusiform (spindle-shaped) body with a relatively small head, its back is blue, the flanks are silvery and the belly is white. The caudal fin is truncated, the flanks feature dark spots in a form of “X” or a crescent, especially above the lateral line. This predatory fish has well developed teeth. Salmon can grow really big, up to 46.8 kg, although their average weight is 4-5 kg and the body length is 50‑100 cm. The life span is up to 10 years, but most fish survive for 4‑6 years.


In Lithuania, salmon breed in their native rivers in October-November, as the water cools down to 5–6 °C, by digging the so-called nests, which are furrows in the substrate up to 1.5 m long and 0.5 m wide. They release and bury some 8‑10 thousand, sometimes up to 30‑40 thousand large eggs reaching 5–7 mm in diameter, thus hiding and protecting them. After the spawning, salmon return to the sea–they breed up to five times in their lifetime, although few fish make it even to the third or fourth reproduction round. Young salmon set off for the sea on their first year or stay in the river for 2-6 years, and upon reaching the sea, they start to feed intensively and quickly gain weight. Various peoples inhabiting the Baltic coasts were using salmon for food as early as 6 000 years ago, and in the territory of Lithuania–at least since 3 000 B.C. These very valuable fish considered a royal delicacy are served salted, dried, hot-smoked or cooked according to countless sophisticated recipes.

Goosander (Mergus merganser, Linnaeus, 1758) A species that both breeds and winters in Lithuania. The population annually breeding in our country consists of some 1 000 pairs. This bird is listed as Category 5 (restored species) of the Lithuanian Red Data Book. The nests are built in hollow trees, various openings and cavities (between boulders, under the roots of trees, etc.), but the birds also successfully occupy customised nest boxes. The breeding population is healthy and keeps growing. The goosander is the largest of the three species of the so-called “sawbill ducks” wintering in Lithuanian waters (the other two are the smew (Mergellus albellus) and red-breasted merganser (Mergus serrator)).

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In comparison with other duck species wintering in the Baltic Sea, the goosander is more likely to choose fresh or brackish water bodies to spend the cold season: open stretches of rivers and streams, lakes and the Curonian Lagoon. Usually it would move into the coastal waters of the Baltic Sea from the Curonian Lagoon if the latter freezes over. Somewhat larger flocks wintering in the coastal zone of the sea are registered in front of the continental coast, where up to 5 000 wintering individuals have been counted in the recent years. Within the last decade or so, the numbers of goosanders spending winters in Lithuanian waters have declined slightly. A trend registered all across the Baltic shows the increasing numbers of birds on the wintering grounds in front of stone and rocky shores and declining wintering stocks in lagoons and enclosed bays. In the entire Baltic Sea, goosanders choose very shallow waters, usually under 5 m deep. According to its food preferences, the goosander is a fish-feeding (ichthyophagous) species, whose diet consists primarily of fish and, to much lesser extent, of other aquatic animals. Its bill is adapted to such type of food, equipped with serrated edges that provide a better grip on slippery fish.

Goosander

Arctic loon

Red-throated loon and Arctic loon (Gavia stellata, Pontoppidan, 1763; Gavia arctica, Linnaeus, 1758) Just as marine ducks, loons breed in freshwater bodies but move to the sea for wintering. The red-throated loon is the northernmost loon species breeding in the lakes and pools of various sizes in the Arctic tundra. The start of the breeding season highly depends on the thawing of the snow cover. These birds

Red-throated loon

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The water column


are solitary breeders, and only large lakes may host a few breeding pairs. The Arctic loon has a much wider distribution range than the red-throated loon. A few pairs regularly breed also in Lithuania. In our country, it is enlisted in the national Red Data Book as Category 1 (endangered) species. The biggest threat faced by the pairs breeding in remote lakes of Lithuania is disturbance caused by recreational visitors. Similarly to grebes, loons are clumsy on the dry land, therefore they build their nests as close to the water as possible. The males are not very different from the females by appearance. In breeding plumage, the red-throated loon is distinguished by a bright brown patch on its throat and grey colour on the rest of its neck and head. The Arctic loon in breeding plumage is also difficult to mistake for another species. Its head and back of the neck are grey, while the throat is covered with a large black patch, the sides of the neck bear black stripes while the black back is decorated with white spots. In their winter plumage, both species loose that distinctive colouration and can be easily confused. The red-throated loon differs from the Arctic loon by its bill pointing slightly upward (the other species has a horizontal bill) and somewhat lighter neck colour. In addition to that, the red-throated loon is a little smaller than its relative. Nonetheless, because of great similarity, both species are often counted together during various censuses in order to avoid misidentification. In the Baltic Sea, loons are usually observed as solitary individuals, less often in small and loose groups. Only during migration these birds can be frequently seen passing or resting in larger groups. Loons winter both in shallow coastal waters and offshore, wherever they find enough food.

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Loons are excellent swimmers capable to dive deep and long in pursue of their main prey–small fish. Because of this hunting pattern they often get entangled in stationary fishing nets in the territories where their wintering grounds overlap with intense fishery zones. The populations of both species have been declining recently, the main threats being disturbance and depredation at the breeding grounds, accidental catches in fishing nets and oil pollution at the wintering grounds.

Great crested grebe (Podiceps cristatus, Linnaeus, 1758) In Lithuania, this bird is observed all year round, the breeding population reaching up to 20 000 pairs. It breeds in the inland water bodies: lakes, ponds, reservoirs, etc. The nest is always built at the edge of the water, among aquatic vegetation, because the bird is almost incapable of walking on dry land. During the breeding season, this grebe is characterised by its feathery head and neck decorations and complex courtship behaviour. In the past, it was intensively hunted for its decorative feathers. The winter plumage is unimpressive, predominated by white colour and shades of grey. Grebes winter at sea, therefore they can be seen in the Baltic coastal waters only outside the breeding period. In winter, this is the only grebe species abundant along Lithuania’s Baltic coast. Some 1 500‑2 000 wintering individuals are counted annually in Lithuanian coastal waters. In the inland waters, only solitary birds or small groups are observed in winter. The great crested grebe is a typical fish-feeder, its main diet consisting of small fish that these birds actively chase underwater. It can also feed on small invertebrates and

amphibians. Contrary to many sea ducks, the wintering distribution of great crested grebe is less predictable, because the birds aggregate at the sites where their main prey–small fish, are abundant. Usually grebes do not produce large aggregations at the wintering grounds, they spent winters dispersed, in solitude or small groups.

Auks Auks are sometimes called the penguins of the Northern Hemisphere. Contrary to penguins, they can fly by frequently flapping their relatively small wings, however, many other features, such as the appearance (with predominant black, dark brown and white colours), upright posture on the dry land and excellent diving skills, make them quite similar indeed. Nevertheless, the two bird groups are not closely related. Unlike many other bird species mentioned in this book, auks rely primarily on their wings rather than their feet to gain speed underwater. They are offshore, or pelagic, species seldom seen from the shore, except for the breeding grounds. The can dive very deeply, over 100 m, but usually feed at the depths up to 30 m.

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In Lithuanian waters of the Baltic Sea, three representatives of the auk family can be observed relatively often: the razorbill (Alca torda), the common murre (Uria aalge) and the black guillemot (Cepphus grylle). Speaking of these birds, the great auk (Pinguinus impennis) could also be mentioned. It was a large (some 80 cm tall) flightless bird that once lived in the North Atlantic–a member of the same family and close relative of the razorbill which can be observed in Lithuania. The mass extermination of these birds for their downs and plundering of their eggs–at first for food and then for collections–resulted in the complete extinction of this species in the middle of 19th century. The last known breeding pair was killed in 1844 on an islet adjacent to Iceland. Auks, especially, the common murre, often breed in large colonies on coastal cliffs, teaming up with other colonial seabird species. The breeding density of murres may reach up to 20 pairs per square metre. Black guillemots nest solitarily or in small colonies. The breeding sites are located on ledges of the cliffs, between pieces of rocks or in wider cracks. The nests are very basic or sometimes non-existent. Razorbills and common murres lay one egg in a clutch, black guillemots may produce 1-2 eggs. In Lithuanian waters, auks are observed only outside the breeding season, in October‑April. In this period the flying auks that are in their winter plumage are very difficult to distinguish to a non-expert observer, because all the three species are of about the same size, body shape and have similar flight patterns. Only black guillemots have much lighter winter plumage compared to razorbills or murres, with white and grey colours prevailing. The easiest way to distinguish a murre from a razorbill is by the shape of the


Black guillemot

Common murre

bill: common murres have slender and sharp bills, while those of razorbills are bulky, deep, compressed on the sides and rounded at the tip. Razorbills are widespread in Europe, East Canada and Greenland. They also breed in the Baltic Sea on its rocky shores of Sweden, Finland, Russia and Estonia. Common murres of the Baltic Sea breed only in Sweden, however, they have a very broad global range, nesting on the coasts of the Pacific, Atlantic and Arctic Oceans. Black guillemots, although also breeding in the Baltic Sea, are widespread much further north than their other two relatives of the auk family– their nesting grounds reach such remote northern territories as Svalbard and Franz Josef Land. Black guillemots often winter right next to the edge of the ice cover, even in remote Arctic areas. All auks usually feed on fish by actively pursuing them underwater. Because of that these birds often get entangled in stationary nets if their feeding areas overlap with commercial fishery zones where stationary nets are used.

Grey seal (Halichoerus grypus, Fabricius, 1791)

Razorbill

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Grey seals are large colonial marine mammals. They are characterised by a pointed snout, rounded head, fusiform body and short tail. A thick layer of fat is stored under the skin. The main propulsive organs in the water are their hind legs which have evolved into broad flippers. The front legs are used for steering and breaking. These animals have good senses of smell and hearing as well as sensitive whiskers called vibrissae, which can sense water turbulence produced by fish and even sound waves. Each vibrissa moves

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The water column

independently and is equipped with 10 times more neural cells than the whiskers of land animals! Grey seals assemble into large aggregations for breeding, moulting and resting, usually on ice or remote islets away from humans. In the Baltic Sea, they grow up to 1.6‑2.1 m, the females reaching 100‑180 kg, while the males can weigh about 300 kg. This is the largest mammal of the Baltic Sea. The females live some 30-40 years, the males–about 10 years less. The cows reach sexual maturity at the age of 4‑5 years. The skin of the grey seal is dark, ranging from dark grey or brown with patches to black. The diet of Baltic grey seals highly depends on the season and fish abundance. It consists of flatfish, Baltic herring, cod, sandeels, smelts, shorthorn sculpins, gobies, sticklebacks. An adult seal can consume some 10-30 kg of fish per day. While hunting, seals can submerge up to 100 m deep and stay underwater for up to 20 min. In the Baltic Sea, grey seals moult in April-June, on floating ice or at land-based rookeries, while their breeding and mating takes place in late February-March. The females give birth to one, sometimes two pups. The grey seal pups weight 12‑15 kg at birth. They are covered in white soft fur which is replaced by adult fur within 1-2 months, although moulting starts already in 7-10 days after birth. The suckling period lasts for only 16-20 days, during which the female ceases feeding and looses some 50-75 kg of her body weight, relying only on the accumulated fat reserve. The mother’s milk has a very high fat content (sometimes reaching up to 60 %), therefore the pup gains about 2.5 kg per day. The females discontinue nursing very abruptly by swimming out to the sea or starting to mate with the males. The


weaned pups usually have reached 40-50 kg by then. As their mothers abandon them the pups fast for 1-4 weeks. This fasting is a critical stage for the grey seal pups, because their fat reserves are only sufficient for a limited period, in which they must learn to swim well and to catch fish. The pups loose about 30 % of their body mass over that time. Smaller baby seals that failed to accumulate sufficient energy reserve risk freezing or starving to death. Each year such exhausted pups are found also on Lithuanian shores. They are sheltered by the Lithuanian Sea Museum, nursed and eventually released back into the Baltic Sea. The weakened pups require a special care and diet. They are given particular meals, consisting of minced herring, fish oil, various vitamins and micro elements. The mixture is tube-fed to the pups, an only a fortnight later, when their stomachs adapt to this food, they receive their first fish. Once the youngsters start eating well and the necessary quarantine period is over, they are transferred into tanks and pools to join their kin. The young seals stay there

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till they completely recover and accumulate enough fat to be returned to the Baltic Sea. The rescued seals are usually released into the wild in spring or autumn, when large schools of Baltic herring arrive to breed near the shore making their survival easier. The released young seals are tagged and named. The pups born in the museum are named by children. Each spring, a competition is announced and children send in their drawings and proposed names for the seal pups. The pups born in the wild are named after a particular location where they were found, such as Palanga, Nemirseta, Preila or Kopgalis. Although the grey seal has no natural enemies in the Baltic Sea, the size of its population has been changing quite significantly within the last century an a half. A little more than a century ago, there were about 80‑100 thousand of them. The intensive hunting throughout the 20th century and dramatic increase of water contamination at the end of the century have reduced the population to 3 000 animals.

The numbers of Baltic grey seals started recovering only Baltic Sea, Kattegat and Skagerrak is some 6 000 individuals after the bans on hunting and use of some especially toxic strong, while the eastern population covering the coasts of fertilisers in agriculture had been introduced. Nowadays Germany, eastern Sweden and sometimes Poland consists of the Baltic population of the grey seal is estimated at about only about 200 individuals. 30 thousand, although there are suspicions that it could actuHarbour seals avoid the open sea and inhabit coastal ally be double of that. Baltic grey seals are currently found all banks, closed bays and areas near large river estuaries. They over the Baltic Sea, although they are most widespread in its tend to lead a sedentary lifestyle sticking to their favourite northern parts: the Gulfs of Bothnia, Riga and Finland. habitats and refraining from distant migrations. A prevailing opinion is that grey seals do not live perThe adult males are about 1.9 m long and weigh manently in Lithuanian territorial waters and only arrive to- 70‑150 kg, while the females reach 1.7 m and 60‑110 kg. The gether with the migratory fish. Although their numbers have colour of males and females is usually the same, ranging markedly increased in the last decade, the exact count is not from light grey to dark brown with black spots, however, the available. These seals are most frequently observed in early belly is always lighter. spring during the period of intense seal migrations, usually The harbour seal is easy to distinguish from the grey as single individuals or pairs, less often in small pods. The seal by the shape of its mouth, where the sides of the lips largest numbers of sightings were registered at the beaches of hang down to produce an inverted “V”. Its head is also Palanga, Smiltynė, Melnragė and Nida, as well as at Karklė, shorter and more rounded than that of the grey seal, and near the cliff of Olando Kepurė. The total of more than 200 resembles the snout of a dog–hence its popular nickname, grey seal sightings have been registered in Lithuania within “the sea dog”. the last quarter of a century. The daily diet of the harbour seal consists of 3‑6 kg of fish. They usually feed individually or in small groups in the Harbour seal coastal waters, although dives of up to 200 m deep have also (Phoca vitulina, Linnaeus, 1758) been registered. The main food is marine fish: flatfish, Baltic or Atlantic herring, cod, eels, sandeels, smelts, etc.–some 30 The harbour seal is the most widespread seal species in the fish species altogether– but they would not miss an opportuworld. It lives in the temperate, subarctic and arctic climatic nity to grab crabs, shrimps and various molluscs, too. zones of the Northern Hemisphere. The global population The lifespan of females lasts 30-35 years, while that of consists of about half a million individuals. The species is di- males is 20-25 years. The bulls are attached to their protected vided into five subspecies. The Baltic harbour seals belong to territories, usually located near the rookeries or migration the subspecies Ph. v. vitulina, whose main population inhab- routes of the cow seals. This way they increase their chances its the coasts of East Atlantic, while the Baltic Sea hosts only to find fertile females. Harbour seals form colonies at their several thousand individuals. The population of western rookeries, however, individual animals always keep certain

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distance. Usually seals lie next to the water edge to be able to escape quickly. Harbour seals mate in the water at about the same time when the young are weaned. The males fight over females, however, they are less aggressive than grey seals. In order to repel other males from their “aquatic” territories and to attract the females, they use vocalisation an specific swimming displays. Gestation lasts for about 10.5 months. In the Baltic Sea, the pups are usually born in June-July on sandy or gravel beaches. On the East Atlantic coasts, the females usually come ashore as the tide starts subsiding, in order to give birth before the new tide arrives. The newborn pups are well developed and capable of swimming right away. The single pup (twins in exceptional cases) is born devoid of the white baby fur which is shed while still in the womb. The newborn pups are 65-100 cm long and weigh 8-12 kg. They spend the first days of their lives mostly in the water, closely following their mothers and coming ashore only to rest. The mother nurses the pup for 4‑6 weeks with a very fatty milk (up to 45 % fat), both in the water and on the dry land. During the lactation period, the pup gains about 0.5 kg daily and soon starts an independent life, where it has to learn hunting and survival skills. In the Baltic Sea, the harbour seal has practically no natural enemies, except humans, who hunt them illegally, contaminate water and cause incidental drowning in their fishing gear. Only young seals might also be threatened by stray dogs, seagulls and ravens. There are only three recorded sightings of this seal species in Lithuania, the first one from 2005, the other two cases from 2014. Although the global population of this

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species is abundant and still increasing or at least stable, the Baltic population is small and vulnerable to external impacts, therefore harbour seals are protected in the Baltic Sea.

Ringed seal (Phoca hispida, Linnaeus, 1758) The ringed seal is the smallest seal species living in the Baltic Sea. Its name was given due to the skin pattern: the animal is covered in dark fur scattered with light ringshaped patches. The Baltic Sea is inhabited by the Baltic subspecies of the ringed seal P.h. botnica. Some 75 % of the Baltic population reside in the northern part of the Baltic Sea, mainly in the Gulf of Bothnia. Another part of the population lives in the Gulfs of Riga and Finland. These seals usually stick to the sea areas that retain ice cover throughout their breeding season. Ringed seals have a special skill of using their teeth to dig burrows in the snow over the ice cover. Such burrows have several air vents and blowholes, giving access to the water straight from the tunnel. The latter are drilled by the seals themselves using their strong claws, or based on the natural cracks in the pack ice. One female usually maintains 4‑6 blowholes which serve as escape routes in case of predator

attack. The burrows shelter the pups from the cold and hide them from predators, such as foxes, thus being essential for their survival. In summer and autumn, when the ice is gone, Baltic ringed seals rest on the solitary rocks peaking above the surface, little islets, or rocky shores. The females reach sexual maturity at the age of 4-6 years. The males reach maturity at about the same age, however, they usually get the first mating opportunity at the age of 8-10 years. The males are slightly larger than the females. The males are slightly larger than the females. The overall length of adults is about 115–136 cm, their weight reaching 40–65 kg. Ringed seals are believed to live long lives–up to 50 years. The breading time is closely linked with the thickness and extend of the ice cover in the Baltic Sea. The pups weight some 4–4,5 kg at birth which takes place in March-May, the peak being in early April. The southernmost populations of the Baltic ringed seals produce young a little earlier, in February‑March. Within the first fortnight of their lives, the pups learn to swim and dive, and become able to escape predators by travelling from one blowhole to another. The nursing lasts for full 5‑7 weeks, until the pups reach about 20 kg. The males remain together with the females throughout the entire nursing period.

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Ringed seals moult in May-June. In the Baltic Sea, these seals feed on local fish (cod, Baltic herring, etc.), enriching their diet with some crustaceans. In Lithuania this species is found in exceptional cases: only two observations have been registered, in 1997 and in 2003. In both cases dead pups of the ringed seal were found– one of them drowned from entanglement in the fishing nets, another dead from multiple injuries. The Baltic population of ringed seals has shrunk dramatically throughout the 20th century, dropping from 190– 220 thousand to 5 thousand individuals. The main reasons of the decline are considered to be hunting and sea contamination with organic chlorides and other toxic substances. In pursuit of rewards in the early 20th century, hunters in Sweden and Finland used to kill about 20 000 ringed seals annually. A complete ban on hunting and killing of Baltic ringed seals was introduced only in 1980 in what was then the Soviet Union, in 1986 in Sweden and in 1988 in Finland. Limited hunting permissions were restored in 1998 in Finland and in 2001 in Sweden. Illegal hunting is suspected to take place throughout the entire distribution range of the Baltic ringed seal. Ringed seals are also threatened by climate change, leading to insufficiently thick and shorter lasting snow cover, which may increase pup mortality due to hypothermia. There are concerns, that in the next 3 decades the southern populations of the Baltic ringed seals might shrink significantly or disappear completely, as a result of climate change, and only the Gulf of Bothnia would remain a sufficiently stable habitat. Although the global population of ringed seals is abundant, in the Baltic Sea they are considered as a vulnerable species and subject to protection.


Harbour porpoise (Phocoena phocoena, Linnaeus, 1758) The scientific name of the harbour porpoise (Phocoena phocoena) originates from the Greek word φώκαινα [phōkaina], meaning a seal or a big seal. They are one of the world’s smallest cetaceans, reaching 1.55 m on the average (males up to 1.43 m, females up to 1.58 m) and weighting around 55 kg (males up to 50 kg, females up to 65 kg). Their life span is about 10-17 years, and the oldest registered animal was 24 years old. These animals live alone or stay in pods of more than 5 individuals. Their diet includes herring, capelin and sprat. The daily consumption reaches some 4 kg of fish, which they sometimes hunt in larger groups, driving them into dense schools. Harbour porpoises are capable of diving to the depths of 200-220 m and holding their breath for up to 5 min., however, usually they take a breath about every minute. As

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all marine mammals, harbour porpoises have to surface for breathing. Their gestation lasts for 10-11 months, and the calves are usually born in late spring or in summer. They suckle their mothers for 8-12 months. These animals live in moderately cool to cold waters of the Northern Hemisphere, mainly in the zones of continental shelf and coastal waters, close to estuaries. Sometimes they even swim into the rivers. Harbour porpoises are not regular residents of Lithuanian territorial waters where they are observed only occasionally. The harbour porpoise is a rapidly declining species threatened with extinction. The Baltic population is estimated to consist of some 450 individuals. In the past, these animals used to be hunted for their meat and fat. Nowadays, the main threats leading to their decline are accidental catches by fishing gear, pollution, eutrophication, disturbance, and shortage of food due to overfishing. Scientists still lack a lot of information about this mysterious Baltic cetacean.

Deep water depressions and dead zones Just as the deserts on the dry land, this realm is an especially harsh place to survive. These deserts, however, are not being fried by the merciless sun and exhausting heat–on the contrary, they are dark and cold. There is no difference between day and night, or spring and autumn. Oxygen, so plentiful in the air we all breathe, is often in shortage down there, so its availability plays the key role in this realm. The “sea snow”, slowly sinking from the surface in complete tranquillity, is deceiving, as it masks continuous changes happening there. 115

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A B

A

Cod

B

Relict isopod crustacean Saduria entomon

Colonies of Beggiatoa bacteria on the surface of the sea bottom

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Deep water dead zones are the seabed areas where the oxygen concentrations are insufficient for most animals. In the Baltic Sea, they usually occur in depressions with the depths exceeding 80‑90 m. At these sites, all organic material is decomposed by bacteria which consume in the process all the oxygen available in the bottom sediments and demersal water layers. Without these resources, no aquatic organism breathing dissolved oxygen can survive at the bottom, therefore in the deep water dead zones one would almost never find the usual benthic fauna: bivalve and gastropod molluscs, crustaceans or echinoderms, such as starfish. The only permanent inhabitants of these dead zones are Beggiatoa bacteria, recognisable as white spots or mats on the seabed. These 200 µm long filamentous bacteria devoid of pigmentation often live in the environments with high concentrations of hydrogen sulphide deadly to most animals. Dead zones had existed also in earlier times, before human activities became significant, however since 1940-50s, with the intensification of agriculture based on the use of various fertilisers, which eventually ended up in the sea, the area of such dead zones has expanded tenfold. Ever increasing quantities of nutrients reaching the sea provoked eutrophication. The latter is characterised by the accelerated summer algal blooms, which presently are considered to be one of the major ecological problems of the Baltic Sea. In autumn, as the water cools down and the blooms are over, the dead microscopic algae sink to the seabed. In the spotlights of submarine survey cameras,

D eeeeppwat w aetre d re d pr e epsrsei o sn s si o an d s daenad d zdoenaed s zones


Colonies of Beggiatoa bacteria at the depth of 116 m in Lithuanian territorial waters of the Baltic Sea

Filamentous chemotrophic bacteria

Beggiatoa bacteria usually live on the surface of bottom sediments. This stratum separates the deeper sediment layers, devoid of oxygen and rich in hydrogen sulphide, from the lowest layer of water which still contains some oxygen. These bacteria are capable of “relocating” from one environment into another–they “collect” hydrogen sulphide from the deeper layers of sediments, then migrate to the seabed surface to oxidise it with the oxygen extracted from the nitrates available there. They also tend to store nitrates “for a rainy day”, when no oxygen might be around, in order to retain capability to oxidise hydrogen sulphide even then. By doing so, the bacteria lock up large quantities of nitrates on the seabed and help to mitigate eutrophication at the sea surface.

(Beggiatoa,Trevisan ,1842)

Scoloplos armiger, Müller, 1776 they appear like snowflakes, therefore such massive descent is sometimes called the “sea snow”. In oceans, this “snow” might be the key food source to many benthic organisms, but in the deep water dead zones of the Baltic Sea, the only organisms awaiting it are bacteria. Only on rare occasions, under persistent hurricane-strength winds, the salty, heavy, and oxygen-saturated North Sea water is pushed into the Baltic and, flowing along the bottom, reaches its central and northern parts. Thus extensive seabed areas are temporarily supplied not only with “refreshed” water suitable for marine life, but also with some North Sea inhabitants arriving with these water masses, such as polychaetes Scoloplos armiger. For a short period, the dead zones spring into life, they also attract mobile relict isopods Saduria entomon, which had previously retreated into shallower locations. This revival of the dead zones may last for a year or two, before the oxygen is depleted and these areas once again turn into the realm of bacteria.

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The genus Beggiatoa was named after Italian medic and botanist F. S. Beggiato. The bacteria are filamentous by shape, and they are known since the middle of the 19th century. They grow by cell division. As one of the cells in a filament dies, the filament breaks at that point thus giving a start to a new filament in the colony. These bacteria consume hydrogen sulphide, toxic to most benthic animals, by oxidising it with the oxygen extracted from nitrates. The seabed colonies of these bacteria are easy to recognise by the pale colour which they gain because of the accumulated sulphur. As hydrogen sulphide is often associated with the oxygen depletion invoked by human activities, and the Beggiatoa colonies avoid higher oxygen concentrations necessary for most other living organisms, they are considered an effective indicator of “disturbed” environmental conditions.

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Scoloplos armiger is an annelid of the class Polychaeta (bristle worms), whose red or red-brown elongated body reaches up to 12 cm and consists of 200 or more segments bearing multitude of short bristles. The eyes are difficult to distinguish, and the 9th - 17th segments are equipped with gills.

Deep water depressions and dead zones


Being widespread in the North Sea and southern Baltic, these polychaetes can be found in both shallow sublittoral and bathyal (up to 2 000 m deep) zones, and even in estuaries. Scoloplos armiger live in all types of soft deposits, however, they prefer silt bottoms where they burrow 10‑15 cm deep and produce burrows lined with mucus. In central Baltic Sea and Lithuanian waters this bristle worm is found only in deep zones. Their small, just a few millimetres long, larvae are thought to be brought in by saline water masses. This explains abundance fluctuations of this species that follow the intensity of the North Sea water inflow into the Baltic Sea: the bigger the input, the denser the Baltic populations of this worm, and the further north they disperse.

Pontoporeia femorata, Krøyer, 1842 Pontoporeia femorata is an amphipod originating from the Arctic seas and nowadays broadly widespread from the Arctic Ocean to the Baltic Sea, where it is more common in

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the southern regions or central part. At some locations, the density of Pontoporeia femorata reaches over 2 000 individuals per sq. m. They can live in deep and cold zones of the Baltic Sea, at the boundaries of deep water dead zones, and they can tolerate low water salinity. By filtering water and feeding on the remains of sunken phytoplankton and other dead organic matter, these amphipods mix up bottom sediments, increase oxygen levels, and regulate the flows of nutrients (nitrogen, phosphorus, etc.). They also forage on bacteria and other microscopic organisms.

Diastylis rathkei, Krøyer, 1841 This unusually shaped crustacean is unlike any other crustacean living in Lithuanian waters. In the western part of the Baltic Sea, it is the main food source of the demersal fish. This species lives on the bottom, but also rises into the water column. Although in central parts of the Baltic Sea, including Lithuanian waters, it lives exclusively in the deep areas, in some other areas it may also be found in quite shallow waters with the depths of around 10 m. In those locations it demonstrates the negative phototaxis, i.e. behaviour, when the organisms react to the light by moving away from it. The animals loose this trait when they settle deeper. For instance, in the North Sea this crustacean is a true fan of great depths and can be found up to 250 m below the surface. As all crustaceans, this species undergo ecdysis, but their exceptional feature is that they rise from the bottom to moult and swim in the water column. No scientific explanation for this strange behaviour has been given so far.

Diastylis rathkei

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Ostracods, or seed shrimps (Ostracoda, Latreille, 1802) Ostracods are one of the most numerous groups of crustaceans, consisting of about 8 000 species. They are relatively small animals of 0.1‑32 mm, however despite the small size, some species are severe predators, hunting in groups and capable of killing a few times larger prey, such as annelids or fish. Some 40 species live in the Baltic Sea. All of them are small, about a millimetre in size. An Australian ostracod Australocypris robusta is notorious for its unusual reproductive features. The spermatozoa produced by the males are 3.6 times longer than the body of the male itself. These ostracods have especially large reproductive organs where the spermatozoa are stored in a coiled form. Nevertheless, many freshwater ostracods reproduce by parthenogenesis (from the Greek, parthenos meaning virgin, and genesis meaning creation) rather than sexually. This term describes such reproduction when an organism develops from a non-fertilised egg. Parthenogenesis among ostracods is thought to be induced by parasitic bacteria which infect the eggs. Such populations consist exclusively of females.

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In Japan, the Caribbean and Australia, some species of ostracods are called “sea fireflies”, because at night they are capable of emitting a bright blue light. With sufficient oxygen supply, this luminescence is produced by reaction of two chemical substances. There are reports, that during the Second World War, the Japanese army has been using these ostracods in the field to read instructions or military maps. Large quantities of these organisms used to be collected, desiccated and ground into powder, which could later be dampened with a few drops of water to produce light whenever needed. Because of their calcium carbonate shell, these organisms preserve well as fossils. The oldest fossils and the oldest identified ostracods date back 488‑444 million years. For this reason, they are among the most useful organisms for palaeontology, which among other things, analyses the sedimentation patterns, the age of different rock formations, and describes climatic conditions that prevailed millions years ago. Ostracods are also found in the pieces of amber, as inclusions. The first such piece of amber was found in the Baltic Sea in 2005, with the the ostracods preserved in it dating back 42‑54 million years. This piece of amber contained a freshwater species of ostracod from the genus Cyclocypris. Ostracods are preyed upon by small demersal fish. Curiously, some ostracods manage to survive even the passage through the digestive tract of juvenile flatfish, and happily go on with their lives upon ejection with the excrement. For that reason they are considered to be especially good indicators of environmental conditions, little affected by fish populations.

Nature conservation

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Why is it necessary to protect nature? The easiest answer to the question why we should protect nature could be put in a simple statement: we, humans, need nature, but nature does not necessarily need us. Nature does not care which species occupy certain niches, which animal communities will settle in a particular territory, what habitats will evolve. Nature is a big whole, shaped by a multitude of different factors, with us, humans, being just one of them. Nature is constantly evolving, and each individual tries to adapt in this changing environment. Changing conditions and ability to adapt to them are the key driving forces of a slow and long process of evolution. As this process goes on, new species occur, and part of the old ones get extinct. Scientists have determined, that in the natural course of evolution, about 15 species would disappear annually. We must admit, however, that human activities affecting nature change various conditions at much faster rate, and many species are unable to adapt that fast. Therefore, according to some scholars, the rates of extinction in some groups of organisms have been accelerated 100 times, and in some others–up to 1000 times or even more. This means that a few tens or even over a hundred species disappear every day. Such rapid loss of biological diversity has been labelled as the “sixth mass extinction event”. The fifth extinction event took place some 65 million years ago. It was then, that the dinosaurs disappeared. It all may sound very abstract, because extinction of species does not happen overnight, and often it takes place far away from us. Or we simply do not notice these species around us, because they have already become very rare or simply are too small to be seen. One such example could be the aquatic warbler, still breeding in Lithuania. This inconspicuous passerine bird breads in just five countries world-wide. Experts are concerned that this warbler may soon join the list of extinct species. The estimates are that 95 % of this bird’s population has been lost within the last 100 years.

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The principles and tools of nature conservation Dependent on the approach, the roots of nature conservation could be found in religious teachings of the ancient scripts, cherishing and protection of the holly sites, or hunting preserves, accessible only to a handful of the privileged ones. Yet there is a common agreement that the modern principles of nature conservation were first applied in the 19th century, with the establishment of the world’s first Yellowstone National Park in the United States in 1872. A little later, in the early 20th century, the designation of protected territories had become more active, as had the conservation movement itself. The then U. S. President Theodore Roosevelt was confronted with two different approaches to nature conservation, which remain relevant even nowadays. During a picnic in the wild together with President Roosevelt, a famous British writer and promoter of wild nature John Moore was discussing about the value of wild nature and the need for the government to step in for its protection. At the same time, the President’s Advisor, Gifford Pinchot, was defending the opinion that nature should be cherished as a valuable resource, necessary for the present and future generations. Both these attitudes remain viable up till now. The first protected territory in Lithuania, Žuvintas Strict Nature Reserve, was established in 1937. The creation of this reserve is usually associated with the name of the most famous Lithuanian naturalist of the last century Tadas Ivanauskas. Although the first marine protected territory is considered to be Fort Jefferson in Florida, founded in 1935, the true starting point of active efforts to preserve natural diversity in the marine environment is associated with the First World Conference on National Parks of 1962, where maritime conservation was given a special focus. Designation of protected areas and performance of special activities therein is one of the most widespread conservation methods world-wide. The established protected territories

A Baltic coast in the Gulf of Finland

There could be many different reasons, why we should protect and cherish natural diversity. Experts working on the ethics of nature conservation, distinguish the following main motivational trends: evolutionary, ethical, utilitarian, aesthetic, and economic. The evolutionary arguments place emphasis on the necessity to preserve genetic diversity in order to secure the continuity of nature and broad adaptation potential. Conservationists following the ethical line of thinking insist that the right to survive is universal and applies to every living organism, and they also speak about our duty to preserve nature for the future generations. The supporters of the aesthetic approach see the necessity to cherish nature first of all because of her beauty and uniqueness. Finally, the camps of utilitarians and economists accentuate the practical benefits and the ecosystem services that nature provides. In modern times of the market economy, predominated by consumption culture, the practical benefits represent the most understandable and acceptable line of arguments to many people. Finding the most important or the best justified motivation to preserve our nature is hardly a feasible task. What really matters, is for everybody to find their own cause.

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experts recreate the conditions necessary for these factors to kick-in, and thus ensure the survival of rare species and habitats. Control of invasive species is one more conservation tool gaining an increasing importance in the modern globalised world. Alien immigrants can seriously disturb an ecosystem and cause substantial damage. Without natural enemies in the new environment, the invasive species can prove deadly to the local ones, by introducing new diseases or occupying a specific niche in the food web. A good example is the round goby, which was first captured in Lithuanian waters in 2002, and since has become one of the most abundant species at our coasts. Gobies are thought to be strong competitors to the local flatfish species and the eelpout. It is quite possible, that gobies, being very numerous and consuming large quantities of molluscs, have caused a significant decline in the numbers of wintering sea ducks, competing for the same food. Unfortunately, control of the abundance of invasive species by capturing, introducing natural enemies, or by some other means is practically impossible in marine ecosystems. Restriction of trade in protected species is yet another conservation instrument. This preventive measure is regulated by the Convention on International Trade in Endangered Species of Wild Fauna and Flora, also known as the CITES Convention. Trade in plant and animal species or products thereof has become one of the key reasons of their extinction. Corals, sharks and many other marine organisms, included in the CITES lists of trade restrictions, become a less attractive commodity and thus can be protected from complete extermination. When certain species occur on the brink of extinction, or when no other means to preserve them are possible or feasible, the programmes of breeding in captivity or reintroduction into new habitats of endangered species are implemented. These conservation measures are carried out with consideration or broadly agreed criteria, that help to assess, whether the sites designated for release into the wild are free of threats, and to make sure, that such actions have no negative impact on other local organisms in that area. Consent of the local human inhabitants is also an important precondition for the application of this conservation tool.

A sea holly in the dunes of Neringa (Curonian Spit)

are provided with nature management plans, indicating special measures aimed to ensure the favourable status of the protected values. In addition, activities, that can produce any negative impact on the protected objects, are restricted. Protected areas also play an important role in public awareness raising, contributing to better knowledge of nature. In Lithuania, protected areas usually cover both natural and cultural heritage, therefore a harmonised coexistence between human and nature is given a special emphasis. However, the creation of protected areas is not the only tool in nature conservation. Remediation of degraded or destroyed habitats is another widespread method, usually integrated with territorial protection. Habitat remediation is more complicated in the marine protected areas, therefore it is applied less frequently than on land. Following the ecosystem-based approach, restoration and maintenance of key ecosystem development factors may also be an option. Storms, fires, grazing, wind erosion or seasonal ice drift are all important factors that certain species are adapted to. For instance, many well known coniferous trees are adapted to natural forest fires, and for some species they are a necessary precondition for propagation by seeds. Wind erosion shapes dune habitats occupied by specially adapted plant and animal species. By applying conservation measures,

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Protected marine areas in Lithuania A range of national protected areas have been designated with the aim to protect marine habitats of Lithuanian coastal waters, which are important from the conservation point of view. They include Baltic Sea Biosphere Polygon and State Marine Reserve of the Baltic Sea. Marine biodiversity is also protected at Curonian Spit National Park and Pajūris (Seacoast) Regional Park, where the Baltic coastal waters comprise a significant part of their territories. Within Lithuania’s exclusive economic zone, the Klaipėda–Ventspils Plateau and the Sambian Plateau are designated as protected areas with the status of a biosphere polygon. In addition to them, back in the year 2000, Birdlife International identified maritime territories, classified as Important Bird Areas (IBAs), which attract significant aggregations of migratory and wintering seabirds. All these protected marine areas are of international importance and constitute a part of the European ecological network of nature protection areas Natura 2000. As many as six protected territories (Baltic Sea and Curonian Lagoon Biosphere Polygons, State Marine Reserve of the Baltic Sea, Curonian Spit National Park, as well as Pajūris and Nemunas Delta Regional Parks) are listed in the HELCOM Marine Protected Areas (MPA) Database. In 2000, Curonian Spit National Park was also included in the UNESCO World Heritage List.

Offshore protected areas Baltic Sea Biosphere Polygon. It was established in 2013 with the aim to protect a valuable

segment of the Baltic ecosystem along the Curonian Spit, with the particular aim to preserve waterbird aggregation sites, designated as Special Protection Areas according to the EU legislation, attracting high numbers of migratory species, such as the little gull (Hydrocoloeus minutus) and wintering species, such as the velvet scoter (Melanitta fusca) and the razorbill (Alca torda). This protected area covers 31 959 ha. Its eastern boundary coincides with the

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Protected areas in Lithuanian waters of the Baltic Sea and Curonian Lagoon

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A goosander family comes to meet the sea

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western boundary of Curonian Spit National Park, while the southern boundary lies along the state border between the Republic of Lithuania and the Russian Federation. This territory is of exceptional importance for velvet scoters and razorbills wintering in the Baltic Sea, as well as for little gulls during their summer migration. Even though the velvet scoter is officially enlisted as vulnerable in the IUCN Red List of Threatened Species, this particular aggregation attracts over 40 000 individuals, therefore Baltic Sea Biosphere Polygon was designated as a Special Protection Area (SPA) of the Natura 2000 network. State Marine Reserve of the Baltic Sea is the only one of its kind in Lithuania, however, it is huge (covers over 14 000 ha of marine area). The reserve was founded in 2005 to protect a valuable sublittoral ecosystem of the Baltic Sea in the segment between Giruliai and Manciškė. It is important for wintering and migratory aggregations of the red-throated loon (Gavia stellata), the Steller’s eider (Polysticta stelleri), the common goldeneye (Bucephala clangula), the goosander (Mergus merganser), and the little gull (Hydrocoloeus minutus). A reef habitat of the European importance (habitat code 1170) is located on the underwater slope. This protected area also bears the status of a Natura 2000 site. Karklė Marine Reserve. State Marine Reserve of the Baltic Sea borders with another unique protected area rich in biodiversity, Karklė Marine Reserve, which is a part of Pajūris (Seaside) Regional Park. Pajūris Regional Park is situated along the Baltic coastline between Klaipėda and Palanga, more than half of its territory stretching into the Baltic Sea. The parks is an interesting diving ground, offering the possibility to inspect some shipwrecks, enjoy the boulder-dominated seascapes and aquatic life. The segment of coast between Olando Kepurė cliff and Nemirseta features numerous large boulders overgrown with algae and molluscs. These are reefs–a highly protected marine habitat, that provides shelter to many plants and animals, constitutes an important spawning ground and sustains large numbers of wintering birds foraging on molluscs and crustaceans. This area offers protection for especially abundant aggregations of wintering waterbirds: the Steller’s eider (Polysticta stelleri), the common goldeneye (Bucephala clangula), the goosander (Mergus merganser) and the little gull (Hydrocoloeus minutus). Klaipėda–Ventspils Plateau Biosphere Polygon. This is a new protected area in the south-eastern part of the Baltic Sea, over the submarine Klaipėda–Ventspils Plateau. Its major part lies within the exclusive economic zone of Lithuania, the rest being in the territorial sea. It starts some 8 km away from the Lithuanian coastline at its southern borderline and some

Protected marine areas in Lithuania


Just as Klaipėda–Ventspils Plateau Biosphere Polygon, this area was designated for the protection of reef habitat–shallower accumulations of bounders towering over the surrounding seabed in various parts of the plateau, featuring rich colonies of mussels and relatively high species diversity of benthic macrofauna. It also attracts large aggregations of wintering long-tailed ducks, velvet scoters and razorbills.

Restrictions of human activities at the marine reserves Migration and wintering periods are especially challenging for birds, because low temperatures and winds, affecting birds during their local flyovers and searches of suitable feeding grounds, drain a lot of energy from them. Any additional disturbance, making them burn their energy to move into another area, or pushing them into less favourable feeding grounds, weaken their condition and shrink their chances to last through the winter. The conservation regimes of the Baltic Sea areas, designated for the protection of natural values, restrict such human activities that could impair the status of wintering and migrating waterbird populations or damage natural marine habitats. Within these territories, hunting on waterfowl is prohibited, while in the periods of migration and wintering, fishing by stationary nets is strictly regulated in order to avoid entanglement and drowning of the diving birds. Protection of natural values of the Baltic Sea is a shared responsibility of several institutions. For instance, monitoring of the status of protected bird species is performed by the administrations of Curonian Spit National Park and Pajūris Regional Park. Control of marine natural resources is a task shared by inspectors and officers from the State Environmental Protection agencies and the Fisheries Service under the Ministry of Agriculture.

The local fishermen have a special name, “šaktarpas“, for the season when the melting ice cover of the Curonian Lagoon is already too thin for walking but still obstructs boating

21 km away at the northern boundary which coincides with the border between the Republic of Lithuania and the Republic of Latvia. The area of the protected zone is about 31 610 ha. This area was designated to protect a deep reef habitat of Community Interest. Because of great depths, the territory is free of macroscopic algae common on shallow reefs, but it hosts a typical reef community–dense colonies of mussels, the Mytilus sp., with the associated fauna: the bay barnacle Amphibalanus improvisus, the bryozoan Electra crustulenta, etc. Wintering waterfowl are also abundant: the velvet scoter (Melanitta fusca), the razorbill (Alca torda), and the long-tailed duck (Clangula hyemalis). In order to preserve this reef habitat of Community Interest along with the wintering aggregations of waterfowl, this biosphere polygon is planned to be included into the Natura 2000 territorial network. Sambian Plateau Biosphere Polygon. This is a territory encompassing part of a unique marine plateau of the south-eastern Baltic Sea with a characteristic seabed profile and a mosaic pattern of boulders, morainic clay loams and sandy loams. The polygon lies in the exclusive economic zone of Lithuania, some 17 km away from the shoreline, and its southern boundary overlaps with the state border between the Republic of Lithuania and the Russian Federation. The area of this protected territory is about 21 120 ha.

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Other protected areas related to the Baltic Sea Curonian Spit National Park. Right next to Baltic Sea Biosphere Polygon, Lithuania’s largest protected marine area, lies Curonian Spit National Park, which is one of the most unique protected areas of our country. It covers the almost 50 km long Lithuanian part of the Curonian Spit together with the coastal waters on both sides: in the Curonian Lagoon and the Baltic Sea. The national park was founded in 1991. Its main protected natural values include the great dune ridge with the ancient drifting parabolic dunes, the sheltered inter-ridge sand plains along both coasts, the humid dune slacks and foredunes, specific vegetation and

139

Protected marine areas in Lithuania


animal life, ethnographic fishermen houses and historical villas, the relics of ancient settlements buried by the sand, and many other objects. The arid and poor sandy soils of the Curonian Spit, frequent and fast weather fluctuations, along with the strong winds, determine the diversity of flora and fauna of the park. The White Sea-Baltic avian migratory route lies along the length of the Curonian Spit, used by some 15 million birds annually. In winter, many thousand strong wintering aggregations of waterfowl settle in the Baltic Sea areas in front of the Curonian Spit. Sea-feeding species include the long-tailed duck (Clangula hyemalis), the red-throated loon (Gavia stelata) the goosander (Mergus merganser), the common goldeneye (Bucephala clangula), the tufted duck (Aythya fuligula), the great crested grebe (Podiceps cristatus), the Steller’s eider (Polysticta stelleri), and the white-tailed eagle (Haliaeetus albicilla) can often be seen gliding over the area. On the sea-facing side of the park, Neringa Marine Reserve was established for the protection of shallow sublittoral seascape ecosystems including habitats of Community Interest. The national park is included in the Natura 2000 ecological network. The Curonian Lagoon. This is a shallow freshwater lagoon of the south-eastern part of the Baltic Sea. The Curonian Lagoon is rich in rare species and habitats. It includes marine habitat types of Community Interest listed as “1130 Estuarties” and “1150 Coastal lagoons”. The lagoon is an important spawning ground and migratory route to many fish and lamprey species. Migratory bird species, including the Bewick’s swan (Cygnus columbianus bewickii), the northern pintail (Anas acuta), the goosander (Mergus merganser), the smew (Mergus albellus), the little gull (Hydrocoloeus minutus), and the white-tailed eagle (Haliaeetus albicilla), form aggregations of international importance in or around this water body. In order to preserve its ecosystem, Curonian Lagoon Biosphere Polygon was established in 2009. Part of the water area of the Curonian Lagoon falls under the territory of Curonian Spit National Park and Nemunas Delta Regional Park. The Curonian Lagoon is included in the Natura 2000 ecological network because of its species and habitats of Community Interest.

References

Aquascope. Learn more about the sea! (2014).

Bilgin S., Ozen O., Samsun O. (2009). Sexual seasonal growth

http://vattenkikaren.gu.se/defaulte.html

variation and reproduction biology of the rock pool prawn,

BACC Author Team (2011). Assessment of Climate Change for the Baltic Sea Basin. Regional Climate Studies, SpringerVerlag Berlin Heidelberg, XXII, 474 p. Bacevičius E. (2002). Ilgasnukiai ruoniai - gyvasis Baltijos

Palaemon elegans (Decapoda: Palaemonidae) in the southern Black Sea. Scientia Marina 73(2), 239–247. Bird C.J., Saunders G.W., McLachlan J. (1991). Biology of Furcellaria lumbricalis (Hudson) Lamouroux (Rhodophyta:

paveldas. Mokslas ir gyvenimas, 12 (540).

Gigartinales), a commercial carrageenophyte. Journal of

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Applied Phycology, 3: 61–81.

Bacevičius E. (2013). Blyškusis Baltijos gelmių senbuvis. http://albatrosas.lt/Blyskusis-Baltijos-gelmiu-senbuvisp639.html#.VvJOGEelTDc

Bitinas A. (2011). Paskutinysis ledynmetis rytinės Baltijos regione. Klaipėda University publishing, 154 p. Bonnie S. (2013). Bladderwrack Herb Effects. 

Bagdanavičiūtė I., Kelpšaitė L., Daunys D. (2012). Assessment of shoreline changes along the Lithuanian Baltic Sea coast during the period 1947–2010. Baltica 25: 171–184.

http://livestrong.com/article/113644-bladderwrack-herbeffects/ Centre for Marine Evolutionary Biology. Idotea balthica. http://cemeb.science.gu.se/research/target-species-

Bajerčiūtė A., Pupienis D. (2012). Baltijos jūros hidrologinį režimą formuojančių hodrometeorologinių veiksmų analizė 1960–2009 m. Geografija, 48 (1): 12-21. Bellafiore D., Gulbinskas S., Umgiesser G., Ferrarin C., Zemlys P. (2013). Investigation of saline water intrusions into the Curonian Lagoon (Lithuania) and two-layer flow in the Klaipėda Strait using finite element hydrodynamic model. Ocean Science 9 (1), 573-584.

imago+/idotea-balthica/ Chivian E., Bernstein A. (eds.) (2008). Sustaining life: How human health depends on biodiversity. Center for Health and the Global Environment. Oxford University Press, New York. Damušytė A. (2011). Lietuvos pajūrio geologinė raida poledynmečiu. PhD thesis Vilnius University. FAO Corporate document repository. Synopsis of biological data on the common shrimp (Crangon crangon). http://fao.org/docrep/005/ac765t/ac765t03.htm

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References


Fava G., Zangaglia A., Cervelli M. (1992). Ecology of Idotea

HELCOM (2010). Towards an ecologically coherent network

Kinne O. (1971). Marine Ecology. Wiley Interscience, London. Leppäranta M., Myrberg K. (2009). Physical Oceanography of

baltica (Pallas) populations in the lagoon of Venice.

of well-managed Marine Protected Areas – Implementation

Oceanologia Acta, 15(6): 651–660.

report on the status and ecological coherence of the

the Baltic Sea. Geophysical Sciences, Springer-Verlag Berlin

HELCOM BSPA network. Baltic Sea Environ. Proc. No. 124B.

Heidelberg, XXIX, 378 p.

Galkus A. (2003). Vandens cirkuliacija ir erdvinė drumstumo dinamika vasarą kuršių marių ir Baltijos jūros Lietuvos akvatorijose. Geografijos metraštis, 36 (2): 48-60. Geppettia L., Tongiorgi P. (1967). Nocturnal Migrations of Talitrus saltator (Montagu) (Crustacea, Amphipoda). Italian Journal of Zoology, 1 (1): 37-40. Gleick P.H. (1996). Water Resources. In: Encyclopaedia of Climate and Weather (ed. S.H. Schneider), Oxford University Press, New York, vol. 2: 817-823. Haahtela I. (1990). What do Baltic studies tell us about the isopod Saduria entomon (L.) Ann. Zool. Fennici, 27: 269–278. Harff J., Björck S., Hoth P. (ed-s) (2011). The Baltic Sea Basin. Central and Eastern European Development Studies (CEEDES). Springer-Verlag, Berlin Heidelberg, XIII, 449 p. Harris B. (2011). Fucus vesiculosus Bladderwrack. Adaptions of Fucus vesiculosus. http://bioweb.uwlax.edu/bio203/2011/ harris_benj/adaptation.htm#

HELCOM (2013). Climate change in the Baltic Sea Area:

J.F. (2003). An ecosystem model of food web and fisheries interactions in the Baltic Sea. 60 (5): 939-950. HELCOM (1986). Water Balance of the Baltic Sea. Baltic Sea Environ. Proc. No. 16. HELCOM (2009). Biodiversity in the Baltic Sea – An integrated thematic assessment on biodiversity and nature conservation in the Baltic Sea. Baltic Sea Environ. Proc. No. 116B. HELCOM (2009). Eutrophication in the Baltic Sea – An integrated thematic assessment of the effects of nutrient

PNAS, 110 (42): 16697-16699. Österblom H., Casini M., Olsson O., Bignert A. (2006). Fish, seabirds and trophic cascades in the Baltic Sea.

Lesutienė J., Gasiūnaitė Z.R., Strikaitytė R., Žilienė R. (2014).

Marine Ecology Progress Series 323: 233–238.

HELCOM thematic assessment in 2013. Baltic Sea Environ.

Trophic position and basal energy sources of the invasive

Proc. No. 137.

prawn Palaemon elegans in the exposed littoral of the SE

development and mortality within the moult cycle of Crangon

Baltic Sea. Aquatic Invasions, 9 (1): 37–45.

crangon (L.). Marine Environmental Research, 2: 287–299.

HELCOM (2013). HELCOM Red List of Baltic Sea species in danger of becoming extinct. Baltic Sea Environ. Proc. No. 140. Herbwisdom.com. Bladderwrack (Fucus vesiculosus). http://herbwisdom.com/herb-bladderwrack.html Iniciatyva „Tvari jūra“. Baltijos jūra – kam ji rūpi… . (2014). http://vembryrsig.hallbarahav.nu/?lang=lt_LT Invasive Species Compendium. Palaemon elegans (Rock shrimp). (2011). http://cabi.org/isc/datasheet/70617 Jankauskienė R., Safonovienė A. (2009). Distribution of sand hoppers (Talitrus saltator, Montag, 1808) on the beach of the Lithuanian Baltic sea. Ekologija, 55 (3–4): 196–203. Jarmalavičius D., Pupienis D., Žilinskas G. (2014). Sea level fluctuation and shoreline evolution on decadal time scale,

Harvey Ch. J., Cox S. P., Essington T.E., Hansson S., Kitchell

Ornes S. (2013). Mussels’ sticky feet lead to applications.

Lithuanian Baltic Sea coast. Journal of Coastal Research, 70: 164-169. Jarmalavičius D., Satkūnas J., Žilinskas G., Pupienis D. (2012).

Lippson A.J., Lippson R. (1984). Life in the Chesapeake Bay. http://chesapeakebay.net/fieldguide/critter/barnacles MarLIN (2006). BIOTIC - Biological Traits Information Catalogue. Marine Life Information Network. Plymouth: Marine Biological Association of the United Kingdom. http://marlin.ac.uk http://marlin.ac.uk

(2009). Atrask Baltijos jūrą, spalvingas ir verdantis jūros gyvenimas. Baltic environmental forum, Latvia, 1–82. Seaweed Industry Association. Furcellaria lumbricalis. (2014). https://seaweedindustry.com/seaweed/type/furcellariaSmith R. J. (2014). Ostracod Research at the Lake Biwa Museum, Japan. Amazing Ostracod Facts.

Niiranen S. (2013). Multiple forces drive the Baltic Sea food web dynamics and its response to environmental change. Summary of Doctoral thesis, Stockholm University, 29 p. NOBANIS – European Network on Invasive Alien species. Gateway to Information on Invasive Alien Species in North and Central Europe. http://nobanis.org Olenin S., Daunys D., Bučas M., Bagdanavičiūtė I. (authors of compilation) (2012). Lietuvos Baltijos jūros aplinkos būklė:

for the period 1993–2008 based on morphometric indicators.

preliminarus vertinimas. Klaipėda University publishing, 74 p.

Environmental Earth Science, 65 (6): 1727–1736.

Ruskule A., Kuris M., Leiputė G., Vetemaa M., Zableckis Š.

lumbricalis

MarLIN, 2014. The Marine Life Information Network.

Dynamics of beaches of the Lithuanian coast (the Baltic Sea)

Jurgelėnaitė A., Šarauskienė D. (2007). Klaipėdos sąsiaurio

Price R.K.J., Uglow R.F. (1979). Some effects of certain metals on

Omstedt A., Elken J., Lehmann A., Leppäranta M., Meier H.E.M., Myrberg K., Rutgersson A. (2013). Progress in physical

http://lbm.go.jp/smith/facts.html Swedish Ice Service. Ice conditions in the Baltic (2007). http://smhi.se/oceanografi/iceservice/ice_condition.htm Telesh I., Schubert H., Skarlato S. (2011). Revisiting Remane’s concept: evidence for high plankton diversity and a protistan species maximum in the horohalinicum of the Baltic Sea. Marine Ecology Progress Series, 421: 1–11. Telesh I., Schubert H., Skarlato S. (2013). Life in the salinity gradient: Discovering mechanisms behind a new biodiversity pattern. Estuarine, Coastal and Shelf Science, 135: 317-327. The Exotics Guide. Non-Native marine species of the North

pralaidumo pokyčio įtaka jūros vandens prietakos į Kuršių

oceanography of the Baltic Sea during the 2003–2014 period.

American Pacific Coast. Mya arenaria. (2014).

marias procesui. Energetika, 53 (2): 52–56.

Progress in Oceanography 128: 139–171.

http://exoticsguide.org/mya_arenaria

Khlebovich V.V. (1968). Some peculiar features of the

Orav-Kotta H., Kotta J. (2004). Food and habitat of the isopod

The Marine Flora & Fauna of Norway. Seawater.no.

enrichment and eutrophication in the Baltic Sea region. Baltic

hydrochemical regime and the fauna of mesohaline waters.

Idotea baltica in the north-eastern Baltic Sea. Hydrobiologia,

Baltic Isopod – Idotea balthica.

Sea Environ. Proc. No. 115B.

Marine Biology 2: 47-49.

514: 79–85.

http://seawater.no/fauna/arthropoda/balthica.html

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143

References


Wildscreen Arkive, Sand hopper (Talitrus saltator). http://arkive.org/sand-hopper/talitrus-saltator Wulff F.L., Rahm L.A., Larsson P. (ed-s.) (2001). A systems analysis of the Baltic Sea. Ecological Studies, 148. Yang S. (2005). New study finds kelp can reduce level of hormone related to breast cancer risk. UCBerkeley News. http://berkeley.edu/news/media/releases/2005/02/02_

Zaiko A. (2005). Balanus improvisus. Baltic Sea Alien Species Database. http://corpi.ku.lt/nemo/balanus.html

Index

Žaromskis R., Pupienis D. (2003). Srovių greičio ypatumai skirtingose Pietryčių Baltijos hidrodinaminėse zonose, Geografija, t. 39(1): 16-23. Žaromskis R., 1996. Okeanai, jūros, estuarijos. Vilnius.

kelp.shtml Alca torda 107, 134, 138

Cerastoderma glaucum 53

eagle, white-tailed 140

Alosa fallax 96

Cerastoredma edule 53

eel, European 57, 58, 66, 76,

Ammodytes tobianus 57

Chlidonias niger 44

Amphibalanus improvisus

Chroicocephalus ridibundus

72, 138

40

102, 133

71, 72, 76 guillemot, black 107, 108

amphipod, relict 54, 55

Cladophora sp. 71, 72 Clangula hyemalis 86, 138, 140

Anguilla anguilla 76

Clupea harengus membras 97

Electra crustulenta 138

gull, common 40, 41, 42

auk, great 107

cockle, common 53

filamentous chemotrophic

gull, European herring 42, 43

auks 107, 109

cockle, lagoon 53

Aythya fuligula 140

cod, Atlantic 22, 23, 24, 25,

barnacle, bay 66, 70, 71, 72, 73, 138

84, 91, 96, 98, 102, 109, 111, 113, 118

eider, Steller’s 66, 85, 86, 137, 140

bacteria 119, 121

gull, black-headed 36, 44, 44 gull, Caspian 42

gull, great black-backed 42, 43 gull, little 42, 134, 137, 140

flounder, European 22, 48, 57, 58, 59, 60, 84

gull, yellow-legged 42 gulls 24, 40, 44, 54, 112

Fucus vesiculosus 39

Beggiatoa 119, 120, 121

Coregonus lavaretus 100

bream, freshwater 82

Crangon crangon 54

bream, vimba 84, 101, 102

Cyclopterus lumpus 80

Gadus morhua 77

bream, white 82

Cygnus columbianus

Gasterosteus aculeatus 78

58, 66, 67, 71, 78, 79, 84,

Gavia arctica 104

95, 96, 97, 98, 99, 102, 103,

Gavia stellata 104, 137, 140

109, 110, 111, 113, 114

bryozoa 138

bewickii 140

Bucephala clangula 137, 140 Diastylis rathkei 122, 123 carrageen, black 36, 66, 67, 71, 76

duck, long-tailed 62, 66, 70, 86, 138, 139, 140

Cepphus grylle 107

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eelpout 66, 76, 80, 82, 84,

107, 140 green branched weed

Anas acuta 140

57, 58, 59, 70, 77, 78, 79,

144

77, 80, 82, 102, 111

grebe, crested 24, 66, 106,

duck, tufted 140

145

Index

Furcellaria lumbricalis 71

goby, round 50, 58, 66, 70, 73, 84, 85, 86, 109, 133

Haliaeetus albicilla 140 Halichoerus grypus 109 herring, Baltic 25, 48, 57,

Hydrocoloeus minutus 42, 134, 137, 140

goldeneye, common 137, 140

Hydroprogne caspia 44

goosander 104, 105, 137, 140

Hyperoplus lanceolatus 57


Idotea balthica 75, 76

Neogobius melanostomus 84

isopod, Baltic 66, 75, 76

Neomysis integer 95, 96

Saduria entomon 48, 55, 56, 57, 78, 86, 118, 120 Salmo salar 103

kittiwake, black-legged 42

opossum shrimp 48, 90, 95, 96

stickleback, three-spined 78, 79 swan, Bewick’s 140

salmon, Atlantic 84, 90, 103 sand gaper 51, 52, 53

Talitrus saltator 37, 39, 40, 141

Larus argentatus 42

Osmerus eperlanus 102

sand hopper 37, 39, 40, 141

tern, Arctic 44

Larus cachinnans 42

Ostracoda 124

sandeel, great 57

tern, black 44

Larus canus 40

ostracods 124

sandeel, small 48, 57, 58,

tern, Caspian 44

Larus marinus 42

103, 111

Larus michahellis 42

Palaemon elegans 75

loon, Arctic 104, 105, 106

Phoca hispida 112

loon, red-throated 48, 104,

Phoca vitulina 111

scophthalmus maximus 58

Phocoena phocoena 114

scoter, common 60, 61, 62

phytoplankton 24, 25, 72,

scoter, velvet 51, 60, 62, 70,

105, 106, 137, 140 lumpfish 66, 80, 81

91, 93, 95, 122

Scoloplos armiger 120, 121, 122

tern, common 36, 44 tern, Sandwich 44 terns 44, 54 turbot 57, 58 Uria aalge 107

134, 137, 138, 139

Macoma balthica 51

Pinguinus impennis 107

sculpin, shorthorn 66, 79, 109

macoma, Baltic 22, 51

pintail, northern 140

seal 24, 26, 58, 75, 91, 98,

Vimba vimba 101

Melanitta fusca 60, 134, 138

plaice, European 59

Melanitta nigra 60

Platichthys flesus 59

seal, grey 90, 109, 110, 112

merganser, red-breasted 104

Pleuronectes platessa 59

seal, harbour 111, 112

Mergellus albellus 104

Podiceps cristatus 106, 140

seal, ringed 26, 112, 113

Mergus merganser 104, 137, 140

Polysticta stelleri 85, 137, 140

shad, twaite 92, 96, 97

Zoarces viviparus 80

Mergus serrator 104

Pontoporeia femorata 122

shrimp, brown 48, 54, 75, 142

zooplankton 24, 25, 57, 58,

Monoporeia affinis 54, 55

porpoise, harbour 24, 91, 114

smelt, European 79, 84, 102, 103

murre, common 24, 25, 90,

prawn, rockpool 75

smew 104

107, 108, 109

100, 103

whitefish, European 92, 100, 101 wrack, bladder 24, 41

79, 91, 93, 95, 98, 102

sprat, European 24, 78,

mussels 22, 23, 66, 67, 69, 70, 71, 73, 74, 75, 86, 138, 139 Mya arenaria 51

razorbill 24, 48, 107, 108, 109, 134, 137, 139 relict isopod crustacean

90, 95, 97, 98, 99, 100, 102, 114 Sprattus sprattus balticus 98

Myoxocephalus scorpius 79

Saduria entomon 48, 55,

Sterna hirundo 44

mysid 48, 90, 95, 96

56, 57, 78, 86, 118, 120

Sterna paradisaea 44

Mytilus sp. 23, 73, 138

146

Rissa tridactyla 42

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Sterna sandvicensis 44

147

Index


Published by: VšĮ Baltic Environmental Forum Lithuania Užupio g. 9/2–17, 01202 Vilnius www.bef.lt

Printed by: Druka Print Mainų g. 5, 94101 Klaipėda www.druka.lt

Edition of 1,700 copies

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THE BOOK OF THE SEA

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T h e r e a l m s o f t h e Ba lt i c S e a


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5

T h e r e a l m s o f t h e Ba lt i c S e a


The word ‘Baltic’ holds many associations of great importance to us: from our childhood memories about splashing in the spatter of the sea and building sand castles, to the Baltic Way–the symbol of our freedom and unity. This is a part of our history and an invaluable treasure. However, contrary to the citizens of many other maritime countries, a few of us are used to fully enjoy the presents of the Baltic Sea, and our acquaintance with it is often limited to summer holidays at the beach. This book is an opportunity to take a closer look at the Baltic Sea, at its extraordinary and unique life. To see it with the eyes of the authors of different chapters, many of whom have spent countless hours at the sea bottom, on research vessels, observing sea birds or exploring variety of fish.

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THE BOOK OF THE SEA

The Book of the Sea. The realms of the Baltic Sea  

A handbook on marine nature conservation