Horse mussel beds

There are four important horse mussel bed communities:

1. Horse mussel (Modiolus modiolus) beds with hydroids and red seaweeds on tide swept circalittoral mixed substrata. Found on the open coast and in tide-swept channels between 5-50m depth. The mussel beds support a diverse range of red seaweeds, sea firs, tube worms, molluscs and sea anemones. Recorded from Shetland, Orkney, the Hebrides and west coast sea lochs, the majority of records are from Scotland.

2. Horse mussel (Modiolus modiolus)  beds on open coast circalittoral mixed sediments . Typically found in current swept areas at depths of 50-100m, the horse mussels support a rich diversity or organisms, especially polychate worms, bivalves and brittlestars. The only known records from Scotland are from Sullom Voe, Shetland and Hoy Sound, Orkney.

3. Horse mussel (Modiolus modiolus) beds with fine hydroids and large solitary ascidians on very sheltered circalittoral mixed substrata. Typically at depths of between 5-30m in very sheltered conditions, the mussel beds support a variety of brittlestars, scallops, crabs and gastropods. Found in Shetland, Orkney, the Hebrides and west coast sea lochs, it is not found anywhere else outside Scotland.

4. Horse mussel (Modiolus modiolus) beds with Chlamys varia, sponges, hydroids and bryozoans on slightly tide-swept very sheltered circalittoral mixed substrata. Found in very sheltered conditions at depths of between 5-30m, the mussel beds support a variety of organisms including the variable scallop, brittlestars, feather stars, crabs, sponges, sea firs, sea mats, and sea squirts. Only a few records occur from the west coast sea lochs, Skye and Bluemull Sound, Shetland.