MBDP-NI: Priority habitat

Blue Mussel Beds

Blue Mussel Beds

Correspondence with existing habitats

UK BAP broad habitat: Littoral sediment, Sublittoral sediment

May be a component part of Annex I habitats

Description: This habitat includes intertidal and subtidal beds of the blue mussel Mytilus edulis on a variety of substrata in a range of conditions from open coasts to estuaries, marine inlets and deeper offshore habitats. Blue mussel beds plays an important part of a healthy functioning marine ecosystem, having a role in coastal sediment dynamics, acting as a food source for over-wintering waders, and in some areas enhancing biodiversity in an otherwise sediment-dominated environment.

Intertidal mussel beds occur on a variety of substrata such as sand, cobbles and pebbles, muddy sand,mud, bedrock and boulders. Mussel aggregations in this habitat are dense, and can support various age classes. The wrack Fucus vesiculosus is often present, attached to the cobbles or mussel shells, and the shells themselves are often encrusted with various barnacles and bryozoans. The spaces between the mussels can provide refuges for a diverse community of organisms, prominent amongst which are the winkles Littorina littorea and L. saxatilis and small shore crabs Carcinus maenas. The infauna of the underlying sediment (except where this is anoxic mud) may feature the gastropod Hydrobia ulvae, the bivalves Macoma balthica and Cerastoderma edule, the crustaceans Corophium volutator, Crangon crangon and Jaera forsmani, and polychaetes such as the sandmason worm Lanice conchilega, the lugworm Arenicola marina and ragworm Hediste diversicolor. Further infaunal sampling has indicated a diverse range of nematodes, oligochates and polychaetes.

In the subtidal, dense mussel beds can form on the upper faces of tide-swept sediment dominated substrata, almost to the exclusion of almost all other species. The common starfish Asterias rubens is often locally abundant as it feeds on mussels, along with other predators such as the crabs Necora puber, Carcinus maenas and Cancer pagurus. Anemones such as Sagartia undata, the dahlia anemone Urticina felina and the daisy anemone Cereus pedunculatus can be found on gravel patches and amongst the mussels themselves. The hydroid Kirchenpaueria pinnata and others characteristic of strong tides and a little scour, such as Sertularia argentea and Tubularia indivisa, may also be present. Ascidians such as Molgula manhattensis and Polycarpa spp. can also feature on subtidal mussel beds, particularly in silty conditions. Infaunal species include the amphipod Gammarus salinus and oligochaetes of the genus Tubificoides. The polychaetes Harmothoe spp., Psamathe cirrhata and Heteromastus filiformis are also characteristic of this habitat.

Blue mussel beds are distributed around the Northern Irish coast, both intertidally and sublittorally.

Associated biotopes:

Threats:

Commercial fisheries: Targeted removal of mussels, physical damage and smothering from use of mobile fishing gear.
Water Quality: Mytilus edulis bioaccumulates pollutants in seawater which may lead to sublethal, and in some cases, lethal responses.
Coastal developments: Physical damage and displacement from infrastructure development, dredging, trenching and cable/pipe-laying.
Anchoring: Physical damage can arise from sustained anchoring and mooring chains.
Bait digging: Removal of mussels as fishing bait and physical damage from associated trampling in the intertidal.

References:

This has been adapted from the UK BAP Priority Habitat description for Blue Mussel Beds on Sediment.

Marine Biodiversity Data Portal - NI

Blue Mussel Beds