Marine Biodiversity Data Portal - NI

Correspondence with existing habitats

Habitats Directive Annex I: Sandbanks that are slightly covered by seawater all the time

Habitats Directive Annex I: Estuaries

Description: Sublittoral sand and gravel habitats occur in a wide variety of environments, from sheltered (sea loughs, enclosed bays and estuaries) to highly exposed conditions (open coast).

Sand and gravel habitats that are exposed to variable salinity in the mid- and upper regions of estuaries, and those exposed to strong tidal currents or wave action, have low diversity and are inhabited by robust, errant fauna specific to the habitat such as small polychaetes, small or rapidly burrowing bivalves and amphipods. The epifauna in these habitats tends to be dominated by mobile predatory species.

Upper estuarine mobile sands, subject to very low fluctuating salinity, are species poor. This habitat is characterised by mysids and amphipods (Gammarus spp).

Coarse sand sediment can occur in sand-wave formations in shallow water, wave exposed and tide-swept coasts. The infauna in this type of habitat is highly impoverished and is typified by small opportunistic capitellid and spionid polychaetes and isopods (Pontocrates arenarius, Haustorius arenarius and Eurydice pulchra) that are adapted to living in a highly perturbed environment. The epifauna is characterised by mobile predators such as crabs (Carcinus maenas and Polybius spp.), hermit crabs (Pagurus bernhardus), whelks (Buccinum undatum), and occasionally sand eels (Ammodytes spp).

Sand mixed with cobbles and pebbles that is exposed to strong tidal streams and sand scour is characterised by conspicuous hydroids (Sertularia cupressina and Hydrallmania falcata) and bryozoans (Flustra foliacea and Alcyonidium diaphanum). These fauna increase the structural complexity of this habitat and may provide an important microhabitat for smaller fauna such as nudibranchs, amphipods and shrimps. Examples of the habitat are to be found at The Skerries (Portrush), Portstewart and Lough Foyle.

Clean stone gravel habitats are characterised by the sea cucumber Neopentadactyla mixta associated with hydroid/bryozoan turfs and red seaweeds. This habitat type has limited recorded distribution Church Bay (Rathlin Island), The Maidens and Strangford Narrows.

Shallow areas with coarse sand swept by tidal currents but sheltered from wave exposure may develop dense beds of the polychaete Lanice conchilega. Dense beds of polychaete tubes reduce near-bed currents and significantly increase sediment stability.

Circalittoral gravels, sands and shell gravel are split into three different biotopes and have communities of high diversity. These habitats are dominated by thick-shelled bivalve and echinoderms species, (e.g. Pecten maximus, Circomphalus casina, Ensis magnus and Clausinella fasciata), sessile sea cucumbers (Neopentadactyla mixta), and sea urchins (Echinocardium cordatum and Spatangus purpureus).

Many of the inshore habitats are important nursery grounds for juvenile commercial species such as flatfishes. Offshore, sand and gravel habitats support internationally important fish and shellfish fisheries

Associated biotopes:

• SS.SCS.SCSVS – Sublittoral coarse sediment in variable salinity (estuaries)
• SS.SCS.ICS – Infralittoral coarse sediment
• SS.SCS.CCS – Circalittoral coarse sediment
• SS.SCS.OCS – Offshore circalittoral coarse sediment
• SS.SSa.SSaVS – Sublittoral sand in variable salinity (estuaries)
• SS.SSa.IFiSa – Infralittoral fine sand
• SS.SSa.IMuSa – Infralittoral muddy sand
• SS.SSa.CFiSa – Circalittoral fine sand
• SS.SSa.CMuSa – Circalittoral muddy sand
• SS.SMu.CSaMu.VirOphPmax.HAs Virgularia mirabilis and Ophiura spp. with Pecten maximus, hydroids and ascidians on circalittoral sandy or shelly mud with stones
  Note - This assemblage is present at Church Bay on Rathlin Island but the sand is mixed with shelly gravel and is not muddy. The sea anemones Arachnanthus sarsi, Halcampoides sp. and Synarachnactis lloydii are present.

• EUNIS code: A5.12, A5.13, A5.14, A5.15, A5.22, A5.23, A5.24, A5.25, A5.26 and A5.3541

• SS.SSa.OSa – Offshore circalittoral sand
  Note - only the highest biotope level has been recorded in this section, all of the above contain sub-biotopes and some of these biotopes contain important biological communities as described in the main body of the habitat description.

• EUNIS code: A5.27

Priority species: Arachnanthus sarsi, Edwardsia timida, Anseropoda placenta, Arctica islandica, Atrina fragilis, Capnea sanguinea, Amphiura (Ophiopeltis) securigera, Astropecten irregularis, Pecten maximus

Threats:

• Renewable energy: Development of off shore wind and tidal installations.
• Pollutants in riverine discharge
• Trawling and aggregate dredging activities: Most flatfish fisheries are found in areas of sandy seabed and are subjected to intensive perturbation by bottom fishing gears. Gravel substrata are also disturbed by scallop dredging. Large bodied, slow growing fauna such as bivalves are sensitive to fishing, as are biogenic reefs.
• Aggregate extraction in licensed areas.
• Other physical disturbances include land claim, construction of marinas and slip ways, the widening and dredging of channels, pipe and cable laying and the construction of sea defences. These activities can alter tidal flow regimes and wave exposure, or result in deposition of sediments that influence the structure of sedimentary habitats.
• Organic pollution from sewage discharge and aquaculture activities leading to anoxic conditions and a decrease in benthic diversity (e.g. polychlorinated biphenyls and tributyl tin), heavy metals and other chemicals. These pollutants have led to decreases in the populations of common whelks in the North Sea and cause DNA breakdown in some marine organisms.
• Oil leakages and shipping accidents lead to localised pollution of sediment organisms.
• Non-native species: non-native species such as the carpet ascidian Didemnum vexillum can overgrow areas of sea, smothering marine life. The American jacknife razor clam Ensis leei could replace native species.

References:

This habitat description has been adapted from the 1994 UK BAP Action Plan for Sublittoral sands and gravels.