Coastal Lagoons

compiled by: Jan Ekebom, Finland

 

1. European Unions Natural Marine Habitat types definitions: 1150 Coastal lagoons

(priority habitat according to the Habitats Directive)

PAL.CLASS.: 21

1.1 Description of the Habitat

Lagoons are expanses of shallow coastal salt water, of varying salinity and water volume, wholly or partially separated from the sea by sand banks or shingle, or, less frequently, by rocks. Salinity may vary from brackish water to hypersalinity depending on rainfall, evaporation and through the addition of fresh seawater from storms, temporary flooding of the sea in winter or tidal exchange. With or without vegetation from Ruppietea maritimae, Potametea, Zosteretea or Charetea (CORINE 91: 23.21 or 23.22).

Flads and gloes, considered a Baltic variety of lagoons, are small, usually shallow, more or less delimited water bodies still connected to the sea or have been cut off from the sea very recently by land upheaval. Characterised by well-developed reedbeds and luxuriant submerged vegetation and having several morphological and botanical development stages in the process whereby sea becomes land.

Salt basins and salt ponds may also be considered as lagoons, providing they had their origin on a transformed natural old lagoon or on a saltmarsh, and are characterised by a minor impact from exploitation.

1.2 Characteristic species

Plants: Callitriche spp., Chara canescens, C. baltica, C. connivens, Eleocharis parvula, Lamprothamnion papulosum, Potamogeton pectinatus, Ranunculus baudotii, Ruppia maritima, Tolypella n. nidifica. In flads and gloes also Chara ssp.(Chara tomentosa), Lemna trisulca, Najas marina, Phragmites australis, Potamogeton ssp., Stratiotes aloides, Typha spp.

Animals: Cnidaria- Edwardsia ivelli; Polychaeta- Armandia cirrhosa; Bryozoa- Victorella pavida; Rotifera - Brachionus sp.; Molluscs- Abra sp., Murex sp.; Crustaceans- Artema sp.; Fish- Cyprinus sp., Mullus barbatus; Reptiles- Testudo sp.; Amphibians- Hyla sp.

 

1.3 Corresponding categories

German classification: "0906 Strandsee", "240601 Brackwassersee im Ostseeküstenbereich".

1.4 Associated habitats

Saltmarshes form part of this complex.

1.5 References

Bamber et al. (1992). On the ecology of brackish lagoons in Great Britain. Aquatic conservation: marine and freshwater ecosystems, 2, 65-94.

Barnes, R.S.K. (1988). The faunas of landlocked lagoons: chance differences and problems of dispersal. Estuarine and Coastal Shelf Science, 26, 309 - 18.

European Commission (2007). Guidelines for the establishment of the Natura 2000 network in the marine environment. Application of the Habitats and Birds Directives. Appendix I: Marine Habitat types definitions. Update of “Interpretation Manual of European Union Habitats” (EU interpretation manual).

Munsterhjelm, R. (1995). The aquatic macrophyte vegetation of flads and gloes, S coast of Finland. Acta Bot. Fennica (in print).

Palmer, M.A., Bell, S.L., Butterfield, I. (1992). A botanical classification of standing waters: Applications for conservation and monitoring. Aquatic conservation: marine and freshwater ecosystems, 2, 125-143.

2. Additional HELCOM information

2.1 Description of the habitat

Lagoons are physiographic features that usually include a complex of various biotope types and habitats. Baltic lagoons are in most cases bay-like features or coastal lakes that are more or less separated from the sea by surrounding land. They are commonly shallow, often with a varying salinity. The salinity of semi-isolated lagoons is usually about the same as in the surrounding sea area while almost or completely isolated lagoons may, due to runoff from the lagoons drainage area, be less saline than the surrounding sea area. The size range is undefined, but large coastal lagoons may have a surface area of some 100 square kilometres or even more and small lagoons (e.g. Fladas or Gloes) a surface area of only a few hectares. Several specific types of lagoons (Bodden, barrier lagoons and Fladas) exist in the Baltic Sea (HELCOM, 1998). On coasts where primary land uplift (up to 8 mm per year) is present, many of the small lagoons are a result of this process in a tilted peneplan. The seafloor/mainland plain is slightly tilted towards the sea and this, in combination with land uplift and siltation, result in a succession where some shallow bays (so called juvenile flads) are gradually forming into more isolated shallow flads and later into gloes.

2.2 Distribution (past and present)

 

Because lagoons are a typical feature of dynamic coasts, they occur or used to occur in all HELCOM sub-regions of the Baltic Sea area.

2.3 Importance (sub-regional, Baltic-wide, global)

Lagoons are known to be biodiversity hotspots, therefore they are of Baltic-wide importance. The physiographic features of lagoons provide important habitats for aquatic and coastal animal and plant species. The benthic flora is often rich and may include threatened and/or declining plants such as charophytes. In some cases the benthic and halophytic vegetation (mainly along the shores) may cover the entire seafloor of the lagoon. The lagoon plant vegetation provides habitat for many aquatic invertebrates and these are suitable food for larger animals such as fish or birds. Fish may use lagoons for spawning or nursery areas for juveniles. Birds use lagoons as feeding grounds during migration or as breeding areas.

2.4 Status of threat/decline

Human activities have caused various pressures in many lagoons which in some cases have resulted in severe or even irreparable damages. Also, the length of pristine shores of lagoons or lagoons in a natural or near natural state is low and steadily decreasing. The exact abundance or cover of threatened or declining lagoons is not known. Lagoons are under threat or decline in all HELCOM sub-regions. According to the HELCOM Red List of Biotopes and Biotope Complexes (HELCOM, 1998) the Baltic-wide threat category is "Heavily Endangered". Lagoons are "priority habitats" of the EU Habitats Directive which means that they are in immediate threat to become completely changed from a European-wide perspective.

2.5 Threat/decline factors

Eutrophication and pollution by drainage from agriculture and forestry and other sources (like traffic and industry) are serious threats and factors of deterioration. They cause often oxygen deficiency in deep water. Decline is also caused by small-scale dredging which, besides releasing nutrients, remove or destroy shallow water habitats and results in periods of anoxia. Human activities in the lagoon may cause resuspension of the sediment which fuel the eutrophication process. Furthermore, humans also use the lagoon shores for building or other activities of which some cause visual, acoustic or physical disturbance to wildlife. Unsustainable fishing methods pose a threat to larger lagoons.

2.6 Options for improvement

One of the main solutions to stop and reverse degradation of lagoons is a general protection of this natural habitat type by law as already performed in some countries. Particularly still undisturbed and natural lagoon areas should become strictly protected. Moreover, programs and measures are needed to restore natural conditions in affected lagoon areas. This includes a drastic reduction of the eutrophication and pollution in the run off area by e.g. introduction of organic farming. Additional protective measures should be: introduction of ecologically sound fishing methods, preservation of natural dynamics (HELCOM Rec. 16/3), restrictions on building activities and any constructions (HELCOM Rec. 15/1), unregulated growth of tourism and harmful recreational activities. EU Member States are obliged to take all appropriate steps to avoid further deteriotion of this priority natural habitat. This includes the obligation to protect this natural habitat type within the Natura 2000 network, and thus to designate as many SACs as necessary to guarantee its favourable conservation status. Plans or projects may only be carried out when they are related to human health, public safety, with importance for the environment or - to the opinion of the Commission - of overriding public interest (Article 6, EC Habitats Directive). As for all natural habitat types an inventory and a monitoring and assessment programme (also for human activities) is obligatory for EU Member States.

2.7 References

HELCOM (1998). Red List of Marine and Coastal Biotopes and Biotope Complexes of the Baltic Sea, Belt Sea and Kattegat - Including a comprehensive description and classification system for all Baltic Marine and Coastal Biotopes. HELCOM-Baltic Sea Environment Proceedings 75, Helsinki Commission. 115 pp. 

Munsterhjelm, R. (1997). The aquatic macrophyte vegetation of flads and gloes, S coast of Finland. Acta Botanica Fennica 157: 1-68.