Encrusting algal communities on exposed Atlantic infralittoral rock

This habitat comprises a community of crustose algae on rocky substrates. It occurs in locations which are exposed or moderately exposed to wave action. Algal cover is extremely poor, and almost completely restricted to encrusting species. Sessile animals are typically encrusting sponges, bryozoans, barnacles, serpulids and vermetids. Vertical surfaces may be occupied by patches of encrusting sponges and Corynactis viridis, while hydroids such as Aglaophenia pulma may be locally abundant. In deeper water the colonial coral Madracis asperula may be present. The herbivory of the sea-urchins is very important for the maintenance of this habitat. 

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.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats