Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

Habitats Directive Annex I: Coastal Lagoons

Description: Saline lagoons occur both naturally and artificially and vary both in size and form. Natural lagoons occur where a sand or shingle barrier to the sea is formed and seawater may percolate through this. Artificial lagoons are often created when engineering works cut off part of an estuary or the sea from direct tidal influence and/or restricts tidal movement.

Some 30 saline lagoons have been identified in Northern Ireland; only three systems are considered natural and all of these occur within the Strangford Lough area and include a brackish wetland at Rathgorman, a series of pools on Granagh Island and a series of salt pans and creeks at The Dorn. The remaining saline lagoons in Northern Ireland are man-made features that have come about as a result of coastal structural works such as road and railway embankments and shoreline stabilisation. Although the majority of lagoons in Northern Ireland are man-made, they may still support specialist communities and thus have a conservation value.

Two types of saline lagoons within the UK and Republic of Ireland have been identified; these included transitional lagoons and coastal lagoons. Both types of lagoon are described as small water bodies (>0.5 km2) in coastal locations scattered throughout the UK and Republic of Ireland. They are typified by very shallow waters with no single channel to the open sea; sea water enters these systems directly during high tides and through seepage. Transitional lagoons are significantly affected by freshwater inputs from diffuse sources or small streams. All saline lagoons in Northern Ireland have been classed as transitional lagoons.

Associated biotopes:

• IR.LIR.Lag – Submerged fucoids, green or red seaweeds (low salinity infralittoral rock)
• SS.SSa.SSaLS – Sublittoral sand in low or reduced salinity (lagoons)
• SS.SMu.SMuLS – Sublittoral mud in low or reduced salinity (lagoons)
• SS.SMx.SMxLS – Sublittoral mixed sediment in low or reduced salinity (lagoons)
• SS.SMp.Ang – Angiosperm communities in reduced salinity

• EUNIS code: A3.34, A5.21, A5.31, A5.41 and A5.54

Priority species: Cerastoderma glaucum, Hydrobia acuta neglecta, Ecrobia ventrosa

Threats:

• Transient lagoons: Many lagoons, particularly in England and Wales, are naturally transient, salinity regimes change as succession leads to freshwater conditions and eventually to vegetation such as fen carr. Some formerly saline sites are now freshwater.
• Infilling of lagoons: The bar-built sedimentary barriers of ‘typical’ coastal lagoons tend to naturally move landwards with time. Lagoons behind them will eventually be in-filled as bar sediments approach the shore.
• Pollution, in particular nutrient enrichment leading to eutrophication, can have major detrimental effects. This may result from direct inputs to the lagoon or from water supply to the lagoon.
• Artificial control of water (sea and fresh) to lagoons can have profound influences on the habitat (many lagoons are often seen as candidates for infilling or land claim as part of coastal development).
• Coastal defence works can prevent the movement of sediments along the shore and lead to a gradual loss of the natural coastal structures within which many coastal lagoons are located.
• Sea level rise: The impact of coastal defences will be compounded by the effects of sealevel rise.

References:

This habitat description has been adapted from the 1994 UK BAP Action Plan for Coastal saltmarsh beds.