BIOTIC

BIOTIC Species Information for Modiolus modiolus
All Taxonomy Biology Distribution Reproduction

Researched by	Lizzie Tyler	Data supplied by	University of Sheffield
Refereed by	This information is not refereed.
Distribution and Habitat
Distribution in Britain & Ireland	Found off all British coasts. Extensive beds are most common on northern or western coasts but absent south of the Irish Sea and Humber estuary.
Global distribution	Recorded from the White sea and Norway, off the Faroes and Iceland, south to the Bay of Biscay and occasionally North Africa. Also from Labrador to North Carolina in the Atlantic and from the Bering Sea south to Japan and California in the Pacific.
Biogeographic range	Not researched	Depth range	0 - 150 m
Migratory	Non-migratory / Resident
Distribution Additional Information	Modiolus modiolus was also recorded as a dominant member of the species rich benthic assemblage found throughout the gravely sediments of St. George's Channel, and the outer regions of Cardigan Bay and Caernarfon Bay (Mackie et al., 1995). Holt et al., (1998; Table 1) lists the predominant forms of horse mussel beds in British waters. Habitat Modiolus modiolus is adapted to live semi-infaunally with an endobyssate attachment to the substratum but may also be found attached to hard substratum, epifaunally in a manner similar to the common mussel, Mytilus edulis. Modiolus modiolus beds vary in size, density, thickness and form. Epifaunal horse mussels carpet steep surfaces and replace Mytilus spp. on offshore structures in cold waters, e.g., in Loch Duich, Loch Long and Loch Alsh (Holt et al., 1998). Semi-infaunal reefs of large individuals about two-thirds embedded into sediment, forming an irregularly clumped layer and younger individuals between the byssal threads of larger individuals. Reefs form due to the build up of a mound of faecal mud and shell debris over several years. Reefs vary in size and height, depending on the build up of faecal mud and water flow rates. In strong tidal streams the beds may not retain the faecal mud and do not form raised beds (Holt et al., 1998). On coarser grounds and in strong currents the horse mussels bind together the coarse sediment forming banks and live nested infaunally within the deposit. Coarse sediment banks formed by horse mussel beds form wave-like mounds or bioherms in the Bay of Fundy up to 3m high and 20m wide and 10s -100s of metres in length, which are visible on sidescan sonar (Wildish et al., 1998; Wildish & Fader, 1998). Similar banks, up to 1m high occur of the north east Isle of Man and Codling Bank, Ireland (Holt et al., 1998). Horse mussel beds may occur as large and continuous banks (biogenic reefs) or as scattered clumps. Holt et al., (1998) noted that extensive horse mussel beds or reefs were restricted to between 5 -50m in UK, although the large reefs recorded in the Bay of Fundy, Nova Scotia occurred at ca 80m (Wildish & Fader, 1998; Wildish et al., 1998).

Substratum preferences	Bedrock Large to very large boulders Small boulders Gravel / shingle Muddy gravel Coarse clean sand Fine clean sand Sandy mud Muddy sand Mud Mixed Biogenic reef Artificial (e.g. metal/wood/concrete) Rockpools Under boulders	Physiographic preferences	Open coast Offshore seabed Strait / sound Sealoch Ria / Voe Enclosed coast / Embayment
Biological zone	Lower Eulittoral Sublittoral Fringe Upper Infralittoral Lower Infralittoral Upper Circalittoral Lower Circalittoral	Wave exposure	Moderately Exposed Sheltered Very Sheltered
Tidal stream strength/Water flow	Strong (3-6 kn) Moderately Strong (1-3 kn) Weak (<1 kn) Very Weak (negligible)	Salinity	Full (30-40 psu)
Habitat Preferences Additional Information
Distribution References	Fish & Fish, 1996, Tebble, 1976, Hayward et al., 1996, Holt et al., 1998, Anonymous, 1999(u), Brown & Seed, 1977, Davenport & Kjørsvik, 1982, Comely, 1978, Brown, 1984, Wildish et al., 1998, Seed, 1976, Mackie et al., 1995, Jones et al., 2000, Wildish & Fader, 1998, Bayne et al., 1976b, Hayward & Ryland, 1990, Julie Bremner, unpub data,