Mussel beds on moderate energy Atlantic circalittoral rock

This habitat occurs on moderately wave-exposed upper circalittoral bedrock subject to strong or moderately strong tidal streams. Mussels Mytilus edulis or Musculus discors can form dense beds, to the exclusion of other species, on the upper faces of bedrock, boulders and mixed substrata. The Musculus biotope occurs in much more wave sheltered and silted situations. There may also be an associated layer of pseudofaeces, forming a thick, silty matrix. 

Indicators of quality:

Both biotic and abiotic indicators have been used to describe marine habitat quality. These include: the presence of characteristic species as well as those which are sensitive to the pressures the habitat may face; water quality parameters; levels of exposure to particular pressure, and more integrated indices which describe habitat structure and function, such as trophic index, or successional stages of development in habitats that have a natural cycle of change over time.

There are no commonly agreed indicators of quality for this habitat, although particular parameters may have been set in certain situations e.g. protected features within Natura 2000 sites, where reference values have been determined and applied on a location-specific basis. The overall quality and continued occurrence of this habitat is, however, largely dependent on the presence of Mytilus edulis or Musculus discors which creates the biogenic structural complexity on which the characteristic associated communities depend. The density and the maintenance of a viable population of this species is a key indicator of habitat quality, together with the visual evidence of presence or absence of physical damage. However, beds of Mytilus edulis at least may disappear (most likely because of predation by starfish) but are likely to re-colonise at some time in the future (which may be several years) dependent on larval recruitment. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats