Sublittoral sand & gravel habitats are the most common habitats found below the level of the lowest tide around the coast of the UK & Ireland. They occur in a range of environments, from sheltered sea loughs, estuaries & enclosed bays, to highly exposed open coasts.
- Site: Mainly sand – mixture of sand and gravel – mainly gravel
- Main Species: invertebrates: polychaetes, isopods, amphipods, bivalves, hydroids, anemones, bryozoans & crustaceans
- Sublittoral sand & gravel habitats have a range of particle structures, ranging from mainly sand through combinations of sand & gravel to mainly gravel. The composition depends on the strength of tidal currents & exposure to wave action.
- The composition of the sediment determines the organisms which are supported. Where loose, coarse sand is present, fully exposed to wave action & swept by strong tidal streams, small or highly mobile polychaetes (marine segmented worms), amphipods, thick shelled & rapidly burrowing bivalves dominate.
- Where sand is mixed with cobbles & pebbles and is exposed to strong tidal streams, hydroids (Sertularia cupressina & Hydrallmania falcata) &bryozoans (Flustra foliacea & Alycyonidium diaphanum) often dominate. These provide microhabitats for amphipods & shrimps. Lough Foyle is an example of such a habitat.
- On exposed coasts with well-sorted medium & fine sands, polychaetes such as Nephtys cirrosa & isopoda including Bathyporeia spp. often occur. Coarse sand habitats support infauna, which are adapted to the highly perturbed environment, such as opportunistic capitellid & spionid polychaetes & various isopods. They also include mobile predators such as crabs (Carcinus maenas & Liocarcinus spp.), hermit crabs (Pagurus bernhardus), whelks & sand eels (Ammodytes spp)
- In relatively stable, sheltered or deeper water habitats, a diverse range of anemones, bivalves, amphipods, polychaetes and mobile and sessile epifauna (invertebrates that are attached to a surface) are found.
- Gravel beds are found when strong tidal currents or wave action prevent finer material from being deposited & tend to occur in water deeper than 10m. Many of these beds are circalittoral (dominated by sessile animals, below algal zone).
Current Status in UK & Northern Ireland
- There are a variety of sublittoral sand habitats in Northern Ireland, ranging from clean mobile sand to fine muddy sand (Erwin et al., 1986). The NISS (Erwin et al., 1986) recorded gravel habitats from the north-east coast, north of Garron Point & Strangford Lough.
- Near-shore deposits occur along the north coast, extending eastwards from Lough Foyle along the Antrim coast, including the Magilligan Foreland beach-ridge plain, on the north-east shore of the Lough.
- The sand community in Outer Church Bay, Rathlin Island is undisturbed & represents one of the most important in NI (B. Picton, pers.comm; NIEA, 2005)
- The north coast has plains of mobile, soft, clean sand. Large areas of rippled sand extend from the shore into deep water on the northern coast off Magilligan Strand, around the Skerries & the main channel of Lough Foyle, where currents are strong (Erwin et al., 1997; NIEA, 2005).
- Sublittoral sand & gravel habitats are subject to a range of anthropogenic factors such as organic pollution, pressure from fisheries for species such as the scallop Pecten maximus & queenies Chlamys opercularis, physical disturbances from land claim, dredging of navigational channels & cable laying. These habitats are also threatened by the addition of wind & marine turbines, which may disrupt marine communities, & through the extraction of marine aggregates. Such physical disturbances are likely to impact populations of slow growing fauna such as bivalves (UK HAP, 1999).
- Lough Foyle
- Rathlin Island
- Ramore Head & The Skerries