Mytilus edulis and/or barnacle communities on wave-exposed Atlantic littoral rock

This habitat type is found in the mid- to upper eulittoral on shores that are moderately or very exposed to wave action. It is characterised by bedrock and boulders dominated by the mussel Mytilus edulis, barnacles Chthamalus spp. and/or Semibalanus balanoides and limpets Patella spp. There is much regional variation in the species and zonation of the barnacles. Amongst the mussels small red algae including Ceramium shuttleworthianum, Corallina officinalis, Mastocarpus stellatus and Aglaothamnion spp. can be found. Two red algae in particular, Porphyra umbilicalis and Palmaria palmata, are commonly found on the Mytilus itself and can form luxuriant growths.The abundance of the red algae generally increases down the shore and in the lower eulittoral they may form a distinct zone in which mussels or barnacles are scarce. The lichen Lichina pygmaea may be prominent, especially in the south, where it can form distinct patches or even a separate zone among the Chthamalus spp.

With decreasing wave exposure F. vesiculosus is able to survive, gradually replacing the barnacles and P. vulgata biotope. On such moderately exposed shores this habitat may occur on steep and vertical faces, while fucoids dominate the flatter areas. In areas of soft rock (e.g. shales), the barnacles may be scarce or absent and the rock dominated by P. vulgata.

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 overtime.

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. Indicators which have been developed for the assessment of ecological quality of coastal water bodies for the Water Framework Directive (WFD) that are relevant to this habitat include a consideration of macroalgae species richness, proportions of different taxa of algae present , and the abundace and coverage of the rocky surfaces by typical species. 

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats