Seagrass Meadows: Student Manual

STUDENT MANUAL

Seagrass Meadows

STUDENT MANUAL

Seagrass Meadows

Credits © 2023 Authors Delmis del C. Alicea Segarra, EdD, Jorge I. Casillas Maldonado, MS, Ivonne Bejarano Rodríguez, PhD Co-Authors Diana M. Beltrán Rodríguez, MS Science Editing Yasmín Detrés Cardona, PhD, Ariel E. Lugo, PhD, Lesbia L. Montero Acevedo, BS Editing Ruperto Chaparro Serrano, MA, Delmis del C. Alicea Segarra, EdD, Cristina D. Olán Martínez, MA Readers Álida Ortiz Sotomayor, PhD Colaborators Carmen Zayas Santiago, MS English Translation and Editing Wilmarie Cruz Franceschi, MA and Stephanie Díaz Pérez, MA Graphic Design and Layout Delmis del C. Alicea Segarra, EdD Information Specialist Theme guide and graphic design for the geological eras and period stamps Alessandra Otero Ramos, MIS Photography Héctor Ruiz Torres, PhD, Luis Rodríguez Matos, BS, Raúl Omar Ortiz Arroyo, MA, Duane J. Sanabria Ponce de León, BS, Oliver Bencosme Palmer, BA, Ruperto Chaparro Serrano, MA, Brenda Soler Figueroa, MS, Edwin Más González, MS, NRCS-NOAA Authorized Photographs Stonebird (Jonathan), Ming-I Weng, Ryan Somma, Tina Negus, Shizhao Authorized Images US Geological Survey, Steve Lew, Alejandro149 Authorized Maps Ron Blakey Authorized Illustrations Ghedoghedo, Karen Carr, Dennis C. Murphy Yerbas Marinas Video Efraín Figueroa Ramírez, BS Buceada virtual Video (Footage and Editing) Rául Omar Ortiz Arroyo, MAG Plena song about seagrasses Lyrics: David R. González Barreto, Music and voice: Leró Martínez Roldán Printing Rául Omar Ortiz Arroyo, MAG, Delmis del C. Alicea Segarra, EdD

Publication Number: UPRSG-E-314 ISBN: 978-1-891719-96-0

Table of Contents Introduction ............................................................................................................................................... 1 Background: Seagrass Meadows ............................................................................................................... 3 What are seagrasses? ...................................................................................................................... 5 Importance of the Seagrass Meadow Ecosystem............................................................................. 7 Differences Between Seagrasses and Seaweeds ............................................................................. 9 Necessary Conditions for Seagrass Growth ................................................................................... 12 The Seagrasses of Puerto Rico ....................................................................................................... 14 Turtle Grass ................................................................................................................................... 16 Manatee Grass .............................................................................................................................. 18 Shoal Grass .................................................................................................................................... 20 Paddle Grass .................................................................................................................................. 21 Ditch Grass .................................................................................................................................... 22 Main Threats to Seagrasses in Puerto Rico ................................................................................... 23 Glossary .................................................................................................................................................... 25 References ................................................................................................................................................ 29

Introduction As part of the Sea Grant Program of the University of Puerto Rico’s goal to promote the conservation and sustainable use of our marine and coastal resources, we present this educational guide to highlight this resource’s importance and foster their preservation for the enjoyment and benefit of future generations. As part of our educational work, Sea Grant has designed a series of Educational Guides for Teachers about different coastal and marine ecosystems found in Puerto Rico, all of which are highly relevant for our archipelago’s ecologic equilibrium.

This student manual features a scientific background about the seagrasses species within our local environment, and a glossary to help students understand the most important concepts about this topic. Additionally, high quality images and photographs are included to show the seagrass meadows and the organisms that live in them. With this manual, children and young people will be able to read and carry out the activities that teachers will offer them in the classroom, as well as admire the beauty that this ecosystem has to offer.

We know this will be very useful for understanding this ecosystem and we hope that the children and youth of Puerto Rico can learn to appreciate it and promote its conservation. We know this will be very useful for understanding this ecosystem and we hope that the children and youth of Puerto Rico can learn to appreciate it and promote its conservation.

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Background

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Seagrass Meadows

What Are Seagrasses?

Seagrasses (marine phanerogams) are flowering and seeding fruit-bearing plants (angiosperms) which are adapted to life in salt-water or brackish water and on sandy or muddy soils rich in organic material and calcium carbonate. These grasses commonly thrive in the infra-littoral zone (Figure 1), permanently underwater, although they may also be found in the littoral zone, on soils periodically covered by water due to the changing tides (Figure 1).

Figure 1. Profile of a sandy beach according to tidal patterns and distribution (high and low). The littoral zone is the coastal area subjected to the direct influence of tidal action. Diagram taken and adapted from UNESCO. 2010. Sandwatch: adapting to climate change and educating for sustainable development. Paris: UNESCO.

Seagrasses often grow in patches on the seafloor, but they can extend to form large, dense meadows.

Seagrass meadows may be composed of a single species (monospecific) or several different species (multispecific) (Figure 2.)

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A B

Figure 2. Seagrass meadows. A. Monospecific seagrass meadow composed of turtle grass. B. Multispecific seagrass meadow composed of mixed turtle and manatee grass.

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Seagrasses, just like mangrove trees, belong to the marine angiosperm family. These plants evolved during the Cretaceous period, about 145 million years ago, from terrestrial angiosperms that adapted to life in an aquatic environment (Figure 3). Seagrasses are able to live completely submerged in seawater, and have a strong root system to anchor themselves to the substrate and help them withstand the action of waves and currents. Additionally, they have the ability to be pollinated in water.

Seagrasses are monocotyledonous and, although they resemble terrestrial grasses, they are not related to them.

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A‐2 Land Plants Green Algae Phytoplankton

Mangroves

Brown Algae

Seagrass

Red Algae Hard Substrate Precambrian First Living Plants

Silurian

Soft Substrate Cretaceous

Evolutionary Timeline

Evolution of Terrestrial Plants

Evlution of Marine Angiosperms

Figure 3. Seagrass evolution on a geological scale. By: Peter Halasz, taken and adapted from: http://en.wikipedia.org/wiki/File:Evolution_ of_seagrasses_Pengo.svg. License: Creative Commons.

Angiosperms: Angiosperms are plants which produce flowers, seeds and fruits. Some examples include passionfruit, avocado and mangoes, among many others.

Brackish: Water that has more dissolved salts than fresh water, but less than seawater.

Carbon Sink : Natural or artificial environment viewed in terms of its ability to absorb carbon dioxide.

Cretaceous: The Cretaceous period is a division in the geological time scale. It is the third and last period of the Mesozoic Era; it began approximately 145.5 million years ago, and ended approximately 65.5 million years ago.

Infralittoral Zone: Part of the coast which is permanently submerged.

Littoral Zone : Coastal zone under the influence of the shifting tides.

Monocotyledons: Group of vascular plants (phanerogams) that produce flowers (angiosperms), in which the seed embryos present only one initial leaf (a single cotyledon). Examples of monocotyledonous plants are: corn, most cereals, tulips and onions, among others.

Phanerogams: Flower-producing, vascular plants (featuring xylem and phloem).

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Importance of the Seagrass Meadows Ecosystem A seagrass meadow is a fundamentally important ecosystem, necessary for our planet’s ecological balance. It provides habitat, food and shelter for several marine species. It also serves as a carbon sink, and helps prevent coastal erosion. These and other factors that make seagrass meadows crucial to the ecosystem are explored in this section.

1. Interactions with Mangrove Forests and Coral Reefs Mangrove forests, seagrass meadows and coral reefs are all connected to one another, and they interact and stabilize the coastal environment. Seagrasses capture sediments and suspended particles with their roots and leaves, keeping the waters clear. Water clarity is important for the well-being of seagrasses and coral reefs, as it allows sufficient sunlight to reach the seafloor for photosynthesis to occur. Oxygen produced through photosynthesis facilitates aerobic decomposition processes and nutrient recycling in coastal areas. Moreover, seagrass meadows absorb large amounts of nutrients and function as natural filters for chemical substances in the marine environment. This is important to maintain a balance between the corals and the macroalgae that inhabit the reefs, since the excessive increase of nutrients in the water causes uncontrolled increases in algae, which can overgrow on top of the corals causing them to suffocate and die. On the other hand, seagrass meadows are highly productive systems that export nutrients and biomass to other ecosystems. For instance, some fish and crustacean species live in seagrass meadows during their juvenile life-stages, and eventually make their way to other marine ecosystems such as the coral reef.

2. Primary Productivity and Biological Diversity Seagrass meadows are highly productive ecosystems that serve as a carbon sink by absorbing large quantities of carbon dioxide and produce oxygen through the process of photosynthesis. This ecosystem, along with tropical and temperate forests, is classified as the most productive in the world.

The high productivity and structural complexity of seagrass meadows increase habitat diversity and therefore marine biodiversity.

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Aerobic Decomposition: Type of decomposition that uses oxygen to breakdown organic material and wastes in order to recycle nutrients.

Biomass: Total organic matter from all the organisms living in a particular place.

Carbon dioxide: A gas that is present in the atmosphere. It is created by the respiration of living beings, by the decomposition of organic material or by the combustion of carbon-based fuels. This gas is essential for photosynthesis to take place.

Detritus: Residue from organic matter fragmentation.

Epiphytes: SRefers to any organism that grows on different surfaces (living and nonliving) using them only as a support, but does not cause direct harm to them (hence, it is not parasitic).

Estuaries: Coastal zones where large bodies of freshwater (such as rivers) meet the sea. These zones are influenced by tidal changes, but are protected from the direct action of waves and winds.

Euryhaline: Organisms that tolerate a wide range of salt concentration. In this case, they tolerate different concentrations of salts in the aquatic environment where they live.

Foraminifera: Small unicellular organisms belonging to the protozoan family. Their body is protected by a delicate shell or testa.

Planktonic organisms: These are organisms, generally microscopic, that live floating in fresh or saltwater (they are weak swimmers).

Sedimentation: Process of accumulation and deposition of sediments.

Substrate: Surface on which an organism lives.

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3. Shelter, Nursery and Food for Many Species Seagrass meadows are home to many organisms such as starfish, sea urchins and clams, which find ideal protection from the strong waves and currents.

Similarly, the meadows shelter the larval and juvenile life-stages of fishes, mollusks, lobsters, and other commercially important species. The surface of seagrass leaves serves as a substrate for various epiphytic algae, sponges and foraminifera, among others. This ecosystem is also home to many species of medicinal importance (Martínez Daranas, 2007).

Seagrass leaves are an important food source for a great variety of marine organisms, including manatees and green sea turtles, both animals currently listed as endangered species. Furthermore, the detritus generated from plant fragmentation is a source of food for many species that live in the sea and on the beach, such as sea cucumbers, crabs and anemones. The decomposition of seagrasses also releases nutrients into the water that are utilized (re-absorbed) by the seagrasses themselves and by certain planktonic organisms. Usually, some seabirds, such as pelicans and gulls, fly over the seagrass meadows in search of food.

4. Erosion Prevention The extensive attachment system of roots and rhizomes of seagrasses helps prevent seabed erosion by enhancing the process of sedimentation (accumulation and deposition of sediments), soil compaction and stabilization. In addition, seagrass leaves help protect shorelines from erosion by dissipating the energy of waves and currents. This ability of seagrasses to trap and hold sediment helps maintain clarity in the water.

Differences Between Seagrasses and Seaweeds Seagrasses are often mistaken for seaweeds. However, there are clear morphological, ecological and physiological differences between the two, some of which are detailed in the following table (Table 1).

Table 1. Differences between seagrasses and seaweeds.

Taken from: Seagrass-watch. http://www.seagrasswatch.org/seagrass.html Seagrasses

Seaweeds

They are multicellular plants with an internal vascular system (xylem and phloem) through which minerals and nutrients are transported to every cell in the organism.

They are non-vascular organisms. Nutrients reach the organism’s cells through diffusion.

They have real roots, stems and leaves They have roots and rhizomes to anchor themselves to the substrate and to absorb nutrients and minerals.

They photosynthesize only within the cells of their leaves.

Reproduction can be sexual (flowers, fruits and seeds) or asexual (rhizomes, roots or shoots).

They have rhizoids, pedicels (thallus) and laminae (fronds).

They lack real roots, stems and leaves.

They have rhizoids to anchor themselves to the substrate, but absorb nutrients from the water through the surface cells of the organism using diffusion.

They photosynthesize with every cell of their body.

Their reproduction is mainly asexual through spores, fragmentation or shoots, but they can also reproduce sexually through gametes.

Diffusion: Process through which molecules flow from an area with higher concentration to one with lower concentration.

Gametes: Cells participating in sexual reproduction. They only have a single copy of each chromosome (they are haploid).

In many animals, we know them as ovum and sperm. When they unite, they form an organism with two copies of each chromosome (diploid), just like humans.

Laminae: Estructura generalmente aplanada de las algas, que se asemeja a la hoja de una planta.

Pedicel: Thin structure that supports the algae, resembling the stem of a plant.

Phloem: Vascular tissue of a phanerogam, which carries sugars and nutrients in ascending and descending order, from the organs that produce them to those which consume and store them.

Photosynthesis: A process that uses solar energy, water, nutrients, plant chlorophyll and carbon dioxide to form plant tissues (for instance, in the form of sugars, fats or proteins).

Rhizoid: A plant root-like structure used by algae to anchor themselves to the soil and stabilize themselves. Unlike real roots, it does not absorb nutrients.

Rhizomes: Subterranean stem of a plant, which grows horizontally and from which new roots and shoots grow. Rhizomes make it easier for the plant to spread quickly through an area.

Shoots: Sprout of a plant that begins to develop, may include stems and leaves Vascular Plants: Plants that have a vascular system (xylem and phloem) for the distribution of water and nutrients throughout the plant.

Xylem: Vascular plant tissue that transports water and inorganic salts that serve as nutrients. This occurs upward throughout the plant, also providing support for the plant.

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Parts of a Seagrass Plant Leaf

Vertical Shoot

Simple Root Rhizome or Horizontal Stem

Figure 4a. Roots, rhizomes and shoots of turtle grass.

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Parts of Seaweed

Laminae

Holdfast

Figure 4b. A seaweed specimen’s laminae and holdfast (attachment structure).

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Necessary Conditions for Seagrass Growth There are several climate zones on Earth, including polar, temperate and tropical. The polar zones are at the northern and southern extremes of the Earth (from the Arctic Circle to 90o latitude in both hemispheres). There, temperatures are extremely cold and rainfall is scarce. These are inhospitable places. The temperate zone, on the other hand, is located between 30o and 60o latitude in both hemispheres, and there are marked differences in temperature and rainfall according to the seasons of the year. These regions are more suitable for life. Meanwhile, tropical zones are warm throughout the year and although there are four seasons, rainfall patterns distinguish two of them: winter and summer.

Most seagrasses are found in tropical (30° N and 30° S) and subtropical regions, between 25° and 40° latitude in both hemispheres. However, some species inhabit temperate zones (Figure 5). Their distribution is regulated by a series of parameters, such as: 1. Temperature: Seagrasses mainly inhabit waters with temperatures above 75°F (24°C) (Figure 5).

However, some species can be found in colder waters (down to 39°F or 4°C).

Figura 5. Diagrama de la distribución mundial de las hierbas marinas. Tomado de Teach Ocean Science http://www.teachoceanscience.net/teaching_resources/education_modules/seagrass/learn_about/.

Polar (<4oC)

Temperate (4-24oC)

Tropical (>24oC)

Seagrass Distribution

2. Salinity: Most seagrasses tolerate a wide range of salinity, so they can be found in both estuaries (low salinity areas where seawater mixes with freshwater) and high salinity areas. Among the Caribbean species, the shoal grass or shoalweed (Halodule wrightii) is the one that best withstands extreme salinity conditions (it is the most euryhaline) (Phillips and Meñez, 1988, cited by Martínez Daranas, 2007).

3. Wave Action: Although they feature strong attachment structures that anchor them to the substrate, seagrasses inhabit coastal areas protected from strong wave conditions and currents: bays, lagoons and estuaries.

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4. Light Availability and Depth: In order to carry out the photosynthesis process, seagrasses require sunlight, therefore, they live in relatively clear and shallow waters where there is good sunlight availability on the seafloor. The penetration of light into the water column determines the maximum depth to which these seagrasses can be distributed. Sediment and nutrient discharge from the shore increases water turbidity and reduces light availability in these environments.

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The Seagrasses of Puerto Rico Although seagrasses are found throughout all latitudes except Antarctica, the vast majority of species inhabit tropical regions. The best developed seagrass meadows in Puerto Rico are found in the southwestern, southern and eastern areas of the island where the insular shelf is wider and shallower than along the northern coast. These areas are also characterized by milder waves and currents than those of the north coast (Figure 6), which facilitates the establishment and development of seagrass meadows.

Figure 6. Distribution of seagrasses in Puerto Rico.

There are approximately 60 species of seagrasses in the world. In the Caribbean region and Puerto Rico, there are five commonly found species: a. Turtle grass (Thalassia testudinum) b. Manatee grass (Syringodium filiforme) c. Shoal grass (Halodule wrightii) d. Paddle grass (Halophila decipiens) e. Ditch grass (Ruppia marítima).

In general, seagrass meadows in Puerto Rico have a vertical zonation (spatial distribution) where shoal grass usually predominates in the shallower area, followed by turtle grass or a mixture of both, then by manatee grass and finally, although not as frequently, by paddle grass in deeper waters (Figure 7). On the other hand, ditch grass lives in brackish or low salinity waters and does not necessarily share spatial distribution with the other seagrasses.

These five seagrass species have morphological differences such as the size and shape of their leaves, flowers and fruits. They also vary in their tolerance to salinity and depth according to the place where they develop.

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Paddle Grass Halophila decipiens

Manatee Grass Syringodium filiforme

Turtle Grass Thalassia testudinum

Figure 7. Vertical zonation of the four (4) seagrass species commonly found in Puerto Rico, along a depth gradient.

Depth

Shoal Grass Halodule wrightii

Turtle Grass

(Thalassia testudinum)

Figure 8. Photograph of a turtle grass meadow.

Turtle grass is the dominant seagrass species in the Caribbean. Its common name derives from its importance as the main food source for the green turtle (Chelonia mydas) as well as for some fish and other herbivorous organisms. Turtle grass lives in high salinity environments, generally protected from strong wave action. It can be found at depths of 10 m (33 ft), but in clear water it can reach depths of up to 30 m (98 ft). This species is able to tolerate direct exposure to air during low tide.

Turtle grass has flat, ribbon-shaped leaves, 0.4 to 1.8 cm (0.16 to 0.71 inches) wide and up to 30 cm (approx. 12 inches) long. The leaves are rounded at the tips and are borne in clusters on short stems. Its flowers are large and can range in color from light greenish-white to pale pink. They produce pods containing multiple seeds that often reach the ground. This herb has a strong anchoring system that includes roots and rhizomes (or horizontal stems) that can penetrate deep into the sediment (up to 25 cm, approx. 10 inches) (Figure 9).

Figure 9. Details of a turtle grass specimen. You can

observe the roots, rhizomes and the vertical stalk. The highlighted square shows a close-up of the seagrass leaf.

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Organisms That Live and Feed upon Turtle Grass

A

B

C

D

E

F

Figure 10. A. Nudibranch or sea slug (mollusk), B. Epiphytes on the leaves of turtle grass, C. Sea cucumber, D. Starfish, E. Sea turtles (The photograph displays a green turtle.), F. Turtle grass flower. (Photo by: Ria Tan, www.wildsingapore.com) Seagrass Meadows: Student Manual

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Manatee Grass (Syringodium filiforme)

Figure 11. Photograph of a manatee grass meadow.

Manatee grass is another common seagrass within our region. It is generally found in muddy or sandy seabeds in the infralittoral zone. This weed is more frequent in stable environments and does not tolerate low salinity conditions. In Puerto Rico, this species is usually found in shallow waters, mingled with turtle grass (Figure 13B), or in monospecific meadows up to 2030 m (approx. 66-100 ft) deep. Manatee grass is the main food of the West Indian manatee (Trichechus manatus), which is considered an endangered species.

Manatee grass has thin, cylindrical (spaghetti-like) leaves, 0.8 to 2 mm wide and up to 50 cm (approx. 20 inches) long. Because it has less surface area than other seagrass species, manatee grass is not a good competitor for sunlight (needed for photosynthesis). However, since its thin leaves generate less wave resistance, this seagrass colonizes and remains in high-energy environments.

Manatee grass normally blooms from January through June (Den Hartog, 1970). This species is dioecious, meaning it has separate male and female plants.

Pollination occurs when pollen released into the water contacts the stigma of the female plant.

Figure 12. Detailed photo of manatee grass.

The cylindrical shape of its leaf can be observed (see highlighted square).

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A

B

Manatee Grass

Figura 13. A. The West Indian manatee (Trichechus manatus) feeds on manatee grass. B. Manatee grass mingled with turtle grass.

Dioecious:: Adjective describing a plant that has distinct male and female individual organisms.

Pollination: The process by which the pollen of a flower is transferred from the stamens (male part of the flower that produces the pollen) to the stigma (receptive part of the flower).

Stigma: Part of the gynoecium or pistil (female part of the flower) that receives pollen during pollination.

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Shoal Grass

(Halodule wrightii)

Figure 14. Photograph of a shoal grass meadow.

Shoal grass is characterized by having flattened, long and thin leaves (thinner than those of turtle grass) that measure between 4 to 10 cm (approx.

1.6 to 4 inches) in length and 2 to 5 cm (approx.

2 to 5 inches) in width. They have two or three teeth at the upper tip. The leaves are grouped in different nodules along the rhizome. Each nodule produces 2 to 5 roots that grow downward and a group of leaves that grows upwards. Its roots are not ramified. They grow on sand or mud in areas greater than 5 m (approx. 16 ft) deep. It can be found in monospecific grasslands or mixed with other grasses (Figure 14).

Nodules: Structure that separates rhizome segments and from which shoots with leaves and/or roots sprout.

Ramified: spreading or branching.

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Figure 15. Close-up photograph of a shoal grass specimen.

You can see the shape of its leaf and the teeth at the tip of the leaf (see highlighted square).

Paddle Grass

(Halophila decipiens) Figure 16. Photograph of a paddle grass meadow.

Paddle grass is characterized by its petiolate leaves (they have a petiole) and oval (shaped like an oar or a paddle) leaves, which have a finely serrated (toothed) edge, and that are born in pairs on rhizomes (or horizontal stems), with a pair of scales (structures with a shape and consistency similar to fish scales) at their base.

These leaves are up to 25 mm (0.98 inches) long and 6 mm (0.24 inches) wide. Among the seagrasses found in Puerto Rico, this species is the least similar to terrestrial seagrasses, as it does not feature a sheath at its base covering its leaves (unlike turtle grass, which does). This grass is an annual plant (it completes its life cycle in one year) that is generally found in deep water, about 30 m (100 ft) in depth. Paddle grass has thin rhizomes (or horizontal stems) that run along the surface of the sand or mud and a root at each node to anchor the plant to the substrate.

Annual plant: Plant that completes its life cycle during the course of a year.

Petiole: A peduncle or a type of stalk that attaches a leaf to the stem.

Figure 17. Detailed photo of a paddle grass leaf.

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Ditch Grass

(Ruppia maritima)

Figure 18. Photograph of a ditch grass meadow.

Photograph courtesy of: Stonebird (Jonathan), CC By NC-SA 2.0

Ditch grass is a species that has a wide geographic distribution and is abundant in coastal lagoons, estuaries and shallow bays in tropical and subtropical regions. Although it is generally found in brackish or very low salinity waters, it has a high tolerance to drastic changes in salinity. Some botanists do not consider ditch grass to be a seagrass but rather a freshwater, salt-tolerant plant (Den Hartohg, 1970).

Ditch grass leaves (Figure 19) are very Figure 19. IPhotograph of a ditch grass specimen. Photograph courtesy slender (1 mm or 0.04 inches) and measure approximately 10 cm (approx. 4 inches) long. of Ming-I Weng, http://www.flickr.com/photos/mingiweng/ Many branches grow from its stem, sometimes reaching up to 0.5 m (0.5 ft) in height. Its anchoring system consists of rhizomes (or horizontal stems) and roots. Its flowers are very small, measuring between 3-5 mm (0.12-0.20 inches) and are found in pairs.

Pollination can occur underwater or on the surface. Its fruits are dark, pear-shaped and grow in clusters.

This grass is considered a valuable source of food for migratory water birds who, in turn, help in its dispersal. Ditch grass can be propagated by seed, rhizomes or plant fragments.

Hydrophilic pollination: Pollination that takes place underwater.

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Main Threats to Seagrasses in Puerto Rico Natural 1. Storms and Hurricanes - Incoming swells associated with storms and hurricanes can be strong enough to uproot and undermine extensive seagrass meadows. Furthermore, the resulting erosion from these events can cause direct physical damage to the seagrasses or indirect damage if the water turbidity increases drastically and reduces sunlight availability, not allowing seagrasses to perform photosynthesis.

2. Climate Change - Floods and droughts associated with global climate change can cause fluctuations in salinity and water temperature. They can also result in seagrasses being exposed to air for prolonged periods of time, which can cause them to dry out. In addition, changes in sea level can affect seagrass zonation.

Anthropogenic (Caused by Human Activity) 1. Eutrophication - Fertilizers and pesticides used in certain land-based activities can reach the coastal zone during rainfall events through the process of erosion and runoff.

These runoffs from residential, agricultural or industrial activities can contain pollutants that endanger the health of marine ecosystems. Excess nutrients in the water can lead to excessive algal blooms, increases in the turbidity of Walking on seagrasses destroys them. the water column, and a reduction in sunlight available to seafloor organisms.

2. Increased Sedimentation- Urban development and some land-based human activities can lead to excessive sediment discharges in coastal areas. As a consequence, turbidity in the water column increases and light penetration decreases, leading to a reduction in the photosynthetic activity of primary producers living in the coastal zone.

This leads to a reduction in the photosynthetic activity of primary producers living on the seafloor.

When boats navigate in shallow areas, their 3. Boat Traffic and Improper Anchoring - The propellers of boat engines in shallow water can scar and fragment seagrass beds. Indiscriminate anchoring in seagrass areas negatively and directly affects these habitats. It is recommended that anchoring buoys be used in areas where seagrass is abundant (if and when available).

propellers can tear up seagrasses.

Dropped anchor in a seagrass bed.

Anthropogenic: This refers to the effects, processes or materials that result from human activities.

Primary Producers: Organisms that produce their own organic matter (autotrophs) through the process of photosynthesis. photosynthesis. Primary producers are the beginning of all food chains and food webs.

Runoff: Rainwater that is not absorbed by a terrain and flows over different surfaces.

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Glossary:

Aerobic decomposition: Type of decomposition that uses oxygen to breakdown organic material and wastes in order to recycle nutrients.

Angiosperms: Angiosperms are plants which produce flowers, seeds and fruits. Some examples include passionfruit, avocado and mangoes, among many others.

Annual Plant: Plant that completes its life cycle during the course of a year.

Anthropogenic: This refers to the effects, processes or materials that result from human activities.

Biomass: Total organic matter from all the organisms living in a particular place.

Brackish: Water that has more dissolved salts than fresh water, but less than seawater.

Carbon Dioxide: A gas that is present in the atmosphere. It is created by the respiration of living beings, by the decomposition of organic material or by the combustion of carbon-based fuels. This gas is essential for photosynthesis to take place.

Carbon Sink: natural or artificial environment viewed in terms of its ability to absorb carbon dioxide.

Cretaceous: The Cretaceous period is a division in the geological time scale. It is the third and last period of the Mesozoic Era; it began approximately 145.5 million years ago, and ended approximately 65.5 million years ago.

Detritus: Residue from organic matter fragmentation.

Diffusion: Process through which molecules flow from an area with higher concentration to one with lower concentration.

Dioecious: Adjective describing a plant that has distinct male and female individual organisms.

Epiphytes: Refers to any organism that grows on different surfaces (living and nonliving) using them only as a support, but does not cause direct harm to them (hence, it is not parasitic).

Estuaries: Coastal zones where large bodies of freshwater (such as rivers) meet the sea. These zones are influenced by tidal changes, but are protected from the direct action of waves and winds.

Euryhaline: Organisms that tolerate a wide range of salt concentration. In this case, they tolerate different concentrations of salts in the aquatic environment where they live.

Foraminifera: Small unicellular organisms belonging to the protozoan family. Their body is protected by a delicate shell or test.

Gametes: Cells participating in sexual reproduction. They only have a single copy of each chromosome (they are haploid). In many animals, we know them as ovum and sperm. When they unite, they form an organism with two copies of each chromosome (diploid), just like humans.

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Hydrophilic: In a broad sense, it refers to something with an affinity for water. In this case, it refers to a plant which is uniquely adapted to life underwater or in aquatic environments.

Hydrophilic Pollination: Pollination that takes place underwater.

Hyper-saline: An environment with a higher salt concentration than sea water.

Infralittoral Zone: Part of the coast which is permanently submerged.

Laminae: Generally flattened structure of algae, resembling the leaf of a plant.

Littoral Zone: Coastal zone under the influence of the shifting tides.

Macrophytes: Large plants (visible to the naked eye) that are adapted to very humid or aquatic environments, such as lakes, ponds, puddles, estuaries, marshes, river banks, deltas or marine lagoons.

Monocotyledons: Group of vascular plants (phanerogams) that produce flowers (angiosperms), in which the seed embryos present only one initial leaf (a single cotyledon). Examples of monocotyledonous plants are: corn, most cereals, tulips and onions, among others.

Nodules: Structure that separates rhizome segments and from which shoots with leaves and/or roots sprout.

Osmoregulation: The active process by which organisms maintain an adequate balance of the concentration of water and dissolved solutes in their bodies.

Pedicel: Thin structure that supports the algae, resembling the stem of a plant.

Peduncle: Branch that connects a leaf, flower or fruit to the plant.

Petiole: A peduncle or a type of stalk that attaches a leaf to the stem.

Phanerogams: Flower-producing, vascular plants (featuring xylem and phloem).

Phloem: Vascular tissue of a phanerogam, which carries sugars and nutrients in ascending and descending order, from the organs that produce them to those which consume and store them.

Photosynthesis: A process that uses solar energy, water, nutrients, plant chlorophyll and carbon dioxide to form plant tissues (for instance, in the form of sugars, fats or proteins).

Planktonic Organisms: These are organisms, generally microscopic, that live floating in fresh or saltwater (they are weak swimmers).

Pollination: The process by which the pollen of a flower is transferred from the stamens (male part of the flower that produces the pollen) to the stigma (receptive part of the flower).

Primary producers: Organisms that produce their own organic matter (autotrophs) through the process of photosynthesis. photosynthesis. Primary producers are the beginning of all food chains and food webs.

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PSU: Acronym that stands for Practical Salinity Units. It substitutes the previous ppt (parts per thousand). A salinity of 35 PSU is considered a standard seawater salinity.

Runoff: Rainwater that is not absorbed by a terrain and flows over different surfaces.

Ramified: Spreading or branching.

Rhizoid: A plant root-like structure used by algae to anchor themselves to the soil and stabilize themselves. Unlike real roots, it does not absorb nutrients.

Rhizomes: Subterranean stem of a plant, which grows horizontally and from which new roots and shoots grow. Rhizomes make it easier for the plant to spread quickly through an area.

Sedimentation: Process of accumulation and deposition of sediments.

Shoots: Sprout of a plant that begins to develop, may include stems and leaves.

Stamen: Male part of the flower that produces pollen.

Staminate flowers: Male flowers or male flowers. They are flowers that have functional stamens, capable of producing pollen, but lack an ovary, or have an infertile ovary.

Stigma: Part of the gynoecium or pistil (female part of the flower) that receives pollen during pollination.

Substrate: Surface on which an organism lives.

Supralittoral Zone: Part of the coast that is not flooded by tides (it is above the upper limit of high tide).

Vascular Plants: Plants that have a vascular system (xylem and phloem) for the distribution of water and nutrients throughout the plant.

Xylem: Vascular plant tissue that transports water and inorganic salts that serve as nutrients. This occurs upward throughout the plant, also providing support for the plant.

Figure 20. Rhizoid structure in seagrasses.

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References: Blanchon, P., Rodríguez R. (2010). Seagrass. Retrieved August 17, 2023 through http://www.icmyl. unam.mx/arrecifes/seagrass.html Den Hartog C. (1970). The sea-grasses of the world. North-Holland Publ. Amsterdam Fourqurean, J. W., Duarte, C.M., Kennedy, H., Marbà, N., Holmer, M., Mateo, M. A., Apostolaki, E. T., Kendrick, G. A., Krause-Jensen, D., McGlathery, K. J. & Serrano, O. (2012). Seagrass ecosystems as a globally significant carbon stock. Nature Geoscience (5), 505–509. doi:10.1038/ngeo1477.

Green E.P and Short F.t . (2003). World Atlas of Seagrasses. Prepared by the UIMEP World Conservation Monitoring Centre. University of California Press, Berkeley, USA. González Lagoa, J.G., González Toro, C. (2010). Encuentro con el mar. Puerto Rico: Programa Sea Grant.

Martínez Daranas, B.A. (2007). Características y estados de la conservación de los pastos marinos del área de interés del archipiélago Sabana-Camagüey, Cuba. Thesis presented as a requirement for obtaining a PhD in Biological Sciences. Accessed through: http://www.oceandocs.net/ bitstream/1834/3405/1/Martinez-Daranas%20ThesisPhD.pdf McKenzie, L. (2008). Sea Grass Educator Handbook. Seagrass-watch. Retrieved August 17, 2013 through http://www.seagrasswatch.org/Info_centre/education/Seagrass_Educators_Handbook.pdf McKenzie, LJ., Yoshida, RL. & Coles, RG. (2006 - 2012). Seagrass-Watch. Retrieved August 17, 2013 through http://www.seagrasswatch.org Seagrass outreach partnership. (2007). Seagrass it’s a live. Retrieved August 17, 2013 through http:// flseagrass.org/index.php Thompson, A. (2012). What is a Carbon Sink? Retrieved July 8, 2014 through http://www.livescience. com/32354-what-is-a-carbon-sink.html

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ISBN978-1-881719-58-8 9781881719960 ISBN

9 781881 719588

9 781881 719960

UPRSG-E-314.

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