Mytilus edulis beds

Common name: Blue mussel

"Mytilus edulis beds are composed of layers of living and dead mussels at high densities, bound together by the byssus threads secreted by the mussels and sometimes overlaying a great deal of accumulated sediment. The three main components are a physical matrix of living and dead shells; a bottom layer of accumulated sediments, mussel faeces and pseudofaeces, organic detritus and shell debris; and an assemblage of associated flora and fauna (Suchanek, 1979)."

"The distribution of Mytilus edulis species complex is circumpolar in boreal and temperate waters, in both the southern and northern hemispheres extending from the Arctic to the Mediterranean in the northeast Atlantic (Soot-Ryen, 1955). Intertidal beds of the blue mussel Mytilus edulis are specific to the OSPAR area. The majority are found in the Waddensea (Netherlands, Germany and Denmark) and in British coastal waters although they also present all along the coast of France and Ireland (Jones et al., 2000). The species occurs in intertidal and sometimes subtidal habitats, under conditions ranging from fully saline to highly estuarine, and is capable of forming dense beds over much of its range. Mytilus edulis is found in a wide range of wave exposures, from all but the very most exposed shores to extremely sheltered habitats. It forms clumps and dense beds on a variety of sediment types, usually in more wave-sheltered conditions. These areas provide increased oxygen and food supplies, and may also help to prevent ‘mussel mud’ (silt, faeces and pseudofaeces) from building up too quickly."

"Although the mussel beds occur in most of the OSPAR area, the majority of Mytilus beds under threat occur in the Waddensea and southern British coastal waters. The extensive, heavily exploited mussel fisheries (especially spat collecting for aquaculture) removed close to the entire stock in the Waddensea between 1988 and 1990 (Dankers et al., 1999), as well as having knock on effects such as an increased mortality for seabirds (e.g., eider ducks) (Kaiser et al., 1998) and affecting the benthic diversity. Jones et al. (2000), Dankers et al. (1999), and others consider that this habitat is under pressure from fisheries activities especially when settlement of spatfall is low."

"Phytoplankton blooms, produced by nutrient enrichment (e.g., industrial and residential sewage discharge, agriculture), are another potential threat to to mussel beds (de Jonge, 1997) and Jones et al. (1999) have suggested that mussel beds could also have intermediate sensitivity to anti-fouling substances and heavy metal contaminants. The decrease of mussel beds has profound effects on predators such as eider ducks and oystercatchers (Kaiser et al., 1998)."

"OSPAR (2001) considered this habitat to be threatened and/or in decline across the whole OSPAR area. The Leiden Workshop concluded that evidence for the decline and threat of intertidal mussel beds was “strong” across the whole OSPAR area. ICES has found sufficient evidence for the decline and threat of this habitat over the whole OSPAR area."

Source: "OSPAR Commission, 2008: Case Reports for the OSPAR List of Threatened and/or Declining Species and Habitats". OSPAR Commission (2008). Retrieved from https://www.ospar.org/site/assets/files/1892/intertidal_mytilus_edulis_beds.pdf, accessed on 2022-02-15