Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

Habitats Directive Annex I: Estuaries

Habitats Directive Annex I: Salicornia and other annuals colonising mud and sand

Habitats Directive Annex I: Spartina swards

Habitats Directive Annex I: Atlantic salt meadows

Habitats Directive Annex I: Mediterranean and thermo-Atlantic halophilous scrubs

Description: Coastal saltmarshes in the UK comprise the upper, vegetated portions of intertidal mudflats, lying approximately between mean high water neap tides and mean high water spring tides. There are two main types of saltmarsh in Northern Ireland, the first and more extensive, is the estuarine type with conspicuous natural transitions from low to upper marsh communities. The second main type is the smaller beach-head type which tends to occur as small pockets on rocky shores and often consists of only one or two middle-marsh communities, with transitions to lower and upper communities truncated.

Saltmarsh vegetation consists of a limited number of salt tolerant species adapted to regular immersion by the tides. A natural saltmarsh system shows a clear zonation according to the frequency of inundation. At the lowest level the pioneer glassworts Salicornia spp. can withstand immersion by as many as 600 tides per year, while transitional species of the upper marsh can only withstand occasional inundation.

The communities of stabilised saltmarsh can be divided into species-poor low-mid marsh, and the more diverse communities of the mid-upper marsh. On traditionally grazed sites, saltmarsh vegetation is shorter and dominated by grasses. At the upper tidal limits, true saltmarsh communities are replaced by driftline, swamp or transitional communities which can only withstand occasional inundation. Saltmarsh communities are additionally affected by differences in climate, the particle size of the sediment and, within estuaries, by decreasing salinity in the upper reaches.

Saltmarsh is a relatively rare habitat in Northern Ireland with an estimate of the total extent of saltmarsh being approximately 250 ha. The saltmarsh in NI equates to only around 0.5% of the total UK saltmarsh (45,500 ha).

The largest of the estuarine saltmarshes are found in the Roe Estuary in Lough Foyle, around Strangford Lough, at Ballycarry in Larne Lough, in the Bann Estuary and at Mill Bay in Carlingford Lough.

Why are they important to wildlife?

Saltmarshes are important habitats for a range of organisms, in particular specialist plant communities and associated animals; and have a high conservation interest. They provide a valuable resource for large numbers of wading birds and wildfowl as they act as high tide refuges for birds feeding on adjacent mudflats. They also support Breeding Waders, Gulls and Terns, and are a source of food for passerine birds particularly in autumn and winter. Species such as Linnet and Twite feed on the seeds of saltmarsh plants during the winter months. Also in winter, Wigeon and Light-bellied Brent Geese feed on a number of saltmarsh plant species. A number of waders use saltmarshes for roosting and feeding such as Oystercatchers, Lapwing, Redshank, Golden Plover and Curlew. A number of specialist invertebrate species are associated with saltmarshes in Northern Ireland including a number of beetle species which are not found elsewhere.

The rare Narrow Mouthed Whorl Snail Vertigo angustior is confined in Northern Ireland to the upper edge of saltmarsh at the Giant’s Causeway and it is a selection feature of the North Antrim Coast Special Area of Conservation (SAC).

In addition to the many plant and animal species that are directly associated with the saltmarsh itself, there are other species that benefit indirectly from saltmarshes. Tidal saltmarshes have been identified as areas of high productivity providing a source of organic matter and nutrients for fish and a variety of invertebrates in adjacent marine habitats.

The variety and abundance of flowering plants within semi-natural habitats provide good sources of pollen and nectar for many of our pollinating insects such as bumblebees, hoverflies, butterflies and moths. For further information on habitat management for pollinators, refer to the All-Ireland Pollinator Plan resources.

Associated biotopes:

• LS.LMp.Sm – Saltmarsh

• EUNIS code: A2.5

Threats:

• Introduced species – the naturalised alien species, Common Cord-grass Spartina anglica, readily colonises mudflats and has spread around the coast and is causing loss in condition in many of our more extensive saltmarshes.
• Climate change – predicted rising sea-levels and increased storminess are likely to squeeze saltmarsh between an eroding seaward edge and fixed flood defence walls.
• Reclamation – for agricultural use, harbours, ports and other infrastructures have reduced saltmarshes to a narrow fringe along estuary shores.
• Sediment dynamics – local sediment budgets may be affected by coastal protection works, or by changes in estuary morphology caused by land claim, dredging of shipping channels and the impacts of flood defence works over the years.
• Agricultural improvement – including re-seeding and draining has affected the upper transitional zones of some saltmarshes in the past and may still occur on a small scale.
• Grazing – has a significant effect on the structure and composition of saltmarsh vegetation and biodiversity by reducing the height of the vegetation and the diversity of the species and potentially increasing erosion. Coastal saltmarsh has been traditionally managed by light, extensive grazing, with a low stocking rate, and it is advised to have a period without grazing between April and October. Overgrazing should be avoided and the poaching should be minimised. In many cases, where potential damage or animal welfare dictates, saltmarsh is best left ungrazed.
• Cutting – cutting of the saltmarsh for turf can affect saltmarsh survival, in particular on smaller sites.
• Recreation – which includes access for sport, bird watching, walking, etc is not well understood but may be locally significant. Boats create wash onto shore which adds to erosion.
• Pollution – from oil, chemicals and litter can potentially destroy saltmarsh vegetation and whilst it usually recovers, sediment may be lost during the period of die-back. Eutrophication due to sewage effluent and agricultural fertiliser run-off has caused local problems of algal growth on saltmarshes.
• Accretion and / or erosion – accretion and development of saltmarsh is occurring on parts of the British coastline. However, this accretion is not sufficient to offset the national loss of saltmarsh and in many cases the newly created saltmarsh differs from those being lost.

References:

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