Fucoids on variable salinity Atlantic littoral rock

Blankets of fucoid seaweeds, dominating sheltered to extremely sheltered rocky shores with variable salinity, such as sea loch or estuaries. The extent of rocky habitat in estuaries can range from a narrow strip restricted to the top of the shore to littoral reef structures extending to the subtidal, particularly in rias. The topography of estuarine rocky shores also varies from flat and gently sloping to rugged reefs and large boulders with many microhabitats.

Rocky habitats in estuaries are typically located in low wave energy environments with reduced salinity, and experience accelerated tidal streams with increased turbidity and siltation. The communities present 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 to communities similar to open coast rock communities towards the mouth of estuaries.  The wrack Pelvetia canaliculata occurs on the upper shore, with  Fucus spiralis  below. The middle shore is dominated by vast areas of  Ascophyllum nodosum, Fucus vesiculosus, or a mixture of both. Fucus serratus covers lower shore bedrock and boulders. Fucus ceranoides can be found on extremely sheltered shores with variable or low salinity as it is more tolerant of reduced salinity than the other fucoids, so tends to replace Fucus spiralis, Fucus vesiculosus and Ascophyllum nodosum towards the upper reaches of estuaries and sea lochs. This biotope may, however, still contain other fucoids, although Fucus ceranoides always dominates.

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. Dominance of fucoids (cover or biomass ratios of fucoids to other macroalgae) or penetration of fucoids along the salinity gradient is used in some countries as a Water Framework Directive parameter for assessing ecological status.

Synthesis of Red List assessment

Confidence in the assessment

Pressures and threats