Coastal lagoons are an important habitat type. A lagoon is defined as an expanse of shallow water of varying salinity and water volume, wholly or partially separated from the sea by a natural barrier.
In different parts of the country, natural barriers of sand, gravel, peat or rock impound lagoons. When they are porous, the barriers allow water to percolate both landwards and seawards thereby altering both the salinity and the volume of the lagoons.
The 1992 European Union Habitats Directive sets out obligations on member states to protect vulnerable habitats. Annex 1 of the Directive targets 233 natural habitats found in the territories of member states that are of Community interest and that require the designation of Special Areas of Conservation (SACs) to achieve their protection. Fifty-eight of these Annex 1 habitats occur in Ireland.
'Priority habitats' are a sub-set of the Annex I list of 233 habitat types. They are defined as being 'priority' because they are considered to be particularly vulnerable and are mainly, or are exclusively, found within the territory of the European Union. By virtue of their priority status they require special site protection measures to ensure their continued survival.
Lagoons are flagged as priority habitat types and we have about ninety of them in Ireland. The National Parks and Wildlife Service (NPWS), one of the technical services of the Department of Culture, Heritage and the Gaeltacht, is the government agency with overall responsibility for managing lagoon biodiversity. The NPWS website at www.npws.ie gives descriptions of all lagoons together with maps, aerial photographs and other useful information.
The water in lagoons is brackish, that is, it is a mixture of freshwater and seawater. The mixture can vary from being very fresh to being very salty. Salinity is a measure of how salty the water is.
Some freshwater plants and animals can live in lagoons if the salinity is low and some marine plants and animals can live in lagoons if the salinity is high. In addition to the freshwater and seawater elements of the plants and animals that are found in lagoons, there is a third component: the lagoonal specialists. These are plants and animals that are more characteristic of lagoons than of any freshwater or seawater habitat. Lagoonal specialists thrive in lagoon conditions.
Since lagoonal specialists depend on lagoons for their continued survival, many of them are threatened with extinction if their special habitats are not conserved.
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