Faunal communities on variable or reduced salinity Atlantic infralittoral rock

The extent of rocky habitat in rias, sea-lochs and estuaries can range from a narrow strip restricted to the top of the shore to littoral reef structures extending to the subtidal. Rocky habitats in these sheltered inlets are typically located in low wave energy environments with reduced salinity, subjected to accelerated tidal streams with increased turbidity and siltation. The associated communities are adapted to these conditions and consequently their composition and character is different to that found on similar substrata on the open coast. Estuarine rocky habitats often display a transition of community types down the length of an estuary, reflecting the different environmental conditions i.e. those at the upper ends of estuaries being specific to ultra-sheltered and low salinity, grading to communities similar to open coast rock communities towards the mouth of estuaries.

At the most diverse end of the scale this habitat may support a rich and exceptionally abundant sessile epibiota of anemones (e.g. Metridium senile and Diadumene sincta), filter feeding sponges (e.g. Halichondria panacea, Hymeniacidon perleve, Haliclona oculata, Raspalia spp., Suberties spp. and Stelligera spp.), bryozoans (e,g, Alcyonidium digitata, Bugula spp.), hydroids (e.g. Sertularella gaudichaudi, Tubularia spp.) and ascidians (e.g. Ascidiella aspersa and Dendrodoa grossularia). Seaweed dominated biotopes are generally poorly developed or absent. In some sea lochs dense mussel Mytilus edulis beds develop in tide-swept channels, whilst upper estuarine rocky habitats in the rias may support particular brackish-water tolerant faunas.

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