Saline lagoons in the Suffolk Coast Maritime Area

Suffolk

132

Natural

History,

Vol. 35

SALINE LAGOONS IN THE SUFFOLK COAST MARITIME NATURAL AREA N. S I B B E T T The S u f f o l k Coast has some of Ihe mosl important saline lagoon systems in Great Britain, including extensive e x a m p l e s of shingle percolation lagoons.

Coastal saline lagoons are a key habitat under the U K Biodiversity Action Plan and are a priority habitat for which Special Areas of Conservation (SACs) should b e identified under the E u r o p e a n U n i o n ' s Habitats and Species Directive. Within Suffolk there are two candidate S A C s which are named " B e n a c r e to Easton B a v e n t s L a g o o n s " and " O r f o r d n e s s - S h i n g l e Street L a g o o n s " respectively.

Recent progress within the Biodiversity Action Plan includes creation of more pools at Benacrc Broad, identification of further lagoons within the Orfordness-Shingle Street c S A C which may be affected by management, the i d e n t i f i c a t i o n of lagoons outside the c S A C , and the creation by the Environment Agency in 1997 of a small lagoon at Buss Creek, Southwold. To maintain up-to-date k n o w l e d g e a b o u t the l a g o o n s , English N a t u r e c o m m i s s i o n e d Dr Roger B a m b e r and his staff f r o m the Natural History M u s e u m to survey the lagoons, for their salinity, integrity, water sources and other aspects of the habitat. They were surveyed in September and October 1998, and their locations are shown on the map.

King's Marshes, Orfordness A group of 18 lagoons were surveyed on K i n g ' s Marshes, Orfordness, which is part of the Orfordness-Shingle Street c S A C . They support a more diverse Community than those previously recorded on K i n g ' s Marshes (Bamber, 1997).

There was a good population of the rare Starlet sea a n e m o n e Nematostella vectensis, a cockle Cerastoderma glaueum, the spire snails Hydrobia ventrosa and Hydrobia neglecta, the large isopod Idotea chelipes and t w o plant lagoon specialists,tasselweed Ruppia sp, and the alga Chaetomorpha linum.

Salinity w a s f o u n d to ränge f r o m 30 to 4 0 parts per thousand, and was probably at the higher ränge of its natural fluetuation. There had been little rainfall (the only freshwater source) over the few weeks before the survey and some of the lagoons were shrinking in size as water evaporated. T h e only thrcat to the lagoons identified was the possibility of the shingle bank protecting them from the sca being eroded away in time. N o habitat m a n a g e m e n t appeared necessary.

Benacre Broad National Nature Reserve The main lagoon on this National Nature Reserve, Benacrc Broad itself, has reduced in area by 4 0 % since 1996 due to incrcased Sedimentation as the coastline has moved shorewards. Areas lost include some which had been lived in by protected species. In Autumn 1996, a new suite of lagoons was dug inland of Benacre Broad to replace the antieipated loss of lagoon area.

The n e w lagoons are all small and of lower salinity than the original lagoon. A s might be expected from their Short history, the animals within the Sediment were sparse although one lagoon did contain tasselweed and

Trans. Suffolk

Nat. Soc. 35

(1999)

SALINE LAGOONS ON THE SUFFOLK COAST

133

Trans. Suffolk Nat. Soc. 35 (1999)

134

Suffolk Natural History, Vol. 35

associated species. At this stage it appears that these lagoons are of such a small size and generally low salinity that the animal communities will become insect-dominated. If it is not possible to retain Benacre Broad itself for longer than the next few years, measures will be needed to conserve saline lagoon habitats and species at the site.

Some of the newer landward pools should be isolated from terrestrial freshwater input and connected to a supply of water from seaward. Salinity needs to rise from the current 0-18 parts per thousand to above 20 parts per thousand and it would be beneficial to enlarge the new pools to seaward. A habitat suitable for lagoon species could then develop.

Reedland Marshes, Dingle Twenty-one lagoons in shinglc grassland were surveyed on Reedland Marshes at Dingle, north of Dunwich (see Plate 6). Their communities included an essentially estuarine sedimentary fauna. There were many N. vectensis in eight sites, fewer at another eight sites, but none in the remaining five sites. A diverse assemblage of species were associated with submerged vascular plants or algae where these occurred. The densities of the spire snail H. neglecta were particularly notable and the rare Lagoon Sand Shrimp, Gammarus insensibilis, was recorded from 13 sites. These lagoons appear to be of SAC quality although they are not included in a lagoonal cSAC. A survey of the surrounding plant communities may be of further value for an overall conservation appraisal.

Maintenance of the shingle bank which protects them from the sea is essential to the lagoons' long-term existence. Maintenance consists of continual movement of shingle onto the bank by bulldozer, leaving residual water-filled scrapes or disrupting established ponds. The principal management requirement for the lagoons is that the sea-defence work is conducted in such a way that damage to the lagoons is avoided.

Buss Creek, Southwold Buss Creek begins near the coast north of Southwold Pier, flows landwards and then turns south to meet the Blyth estuary west of the harbour. Its connection to the river is via a sluice gate, so it is only tidal at the lower 50m.

The rest of Buss Creek is a ditch filled with reed, Phragmites australis.

An area at its upper end was cleared of reeds in 1997 to make a new saline lagoon. The resultant 0-25 ha open water with reed debris on mud unfortunately had not become saline. No salt water comes from the shore or upstream from the Blyth estuary. The only fauna detected was a stickleback fish, freshwater insect larvae and oligochaete worms. The adj acent boating pond had a higher salinity at 8 parts per thousand, but was of little conservation interest.

Summary This survey shows that the specialist lagoonal interest of the Suffolk Coast Maritime Natural Area is greater than previously thought. Diverse communities were found and good populations were present of the rare species Starlet sea anemone Nematostella vectensis (see Plate 5), the lagoonal sand shrimp,

Trans. Suffolk Nat. Soc. 35 (1999)

SALINE LAGOONS ON THE SUFFOLK COAST

135

Gammarus insensibilis and thc spire snail, Hydrobia neglecta. Howcvcr, somc sitcs, notably Bcnacre Broad, have dcclincd in area and in spccics divcrsity.

This survcy shows Ihat creating new lagoons is not casy, requiring as thcy do a significant saline input and opportunities for wholly aquatic invcrtcbrates to colonise. Only in tcn or twenty years time will we bc able to decidc upon thc success or otherwisc of lagoon creation schemes.

More detailed survey results can be found in Bamber (1999).

Acknowledgements English Naturc gratefully acknowlcdgcs the financial contributions and practical assistance from thc Environment Agency and The National Trust.

References Bamber R. N. (1997). Assessment of saline lagoons within Special Areas of Conservation. English Nature Research Report, no 235.

Bamber R. N. (1999). Survey of selected saline lagoons, Suffolk Coast, September 1998. English Nature Research Report, no 300.

Nicholas Sibbett English Nature Regent House 110 Northgate Street Bury St Edmunds Suffolk IP33 1HP

Odd colour form of Green-winged Orchid, Orchis morio, at Monewden The Suffolk Wildlife Trust reserve at High House, Monewden (TM227582) is noted for its abundance of Green-winged Orchid. These flowers are usually a reddish purple, and there is generally a random scattering of white-flowered (but still green-winged) plants among them, together with a ränge of intermediate colour forms including pink, and pink and white. However, each flower is similar to the others on any given stem.

Visiting the reserve on 2 May 1999, I came across a plant with white flowers, white-and-purple flowers and purple flowers, on different sides of the same stem (see Plate 13). There was no sign of fasciation or othcr abnormality, nor of any environmental reason for the unusual form. The location was at thc north end of the third (oblong) field, not far from the field gateway, and surrounded by normal individuals.

I found no mention of this phenomenon in any of my reference books, so I sent a note with a photograph to Martin Sanford, who likewise had not encountered it in thc orchid family. He had seen something similar in Larkspur, and thought it might be a chimera of two genetic types rather than a partial albinism.

Anna Cordon, 1 Karen Close, Ipswich, IP1 4LP

Trans. Suffolk Nat. Soc. 35

(1999)

Plate 6: Saline lagoons at Reedland Marshes near Dunwich (p. 134). The rare Lagoon Sand Shrimp, Gammarus insensibilis and high densities of the Spire snail, Hydrobia neglecta were found here in 1998.

Plate 5: Starlet Sea Anemone, Nematostella vectensis Stephenson, with egg masses. This Biodiversity Action Plan priority species has been found in several saline lagoons (p. 134) and on Havergate Island (p. 57) in 1998.