Description of biotope or habitat type

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   Fucus vesiculosus on full salinity moderately exposed to sheltered mid eulittoral rock

Description

Moderately exposed to sheltered mid eulittoral bedrock and large boulders characterised by a dense canopy of the wrack Fucus vesiculosus (Abundant to Superabundant). Beneath the seaweed canopy the rock surface has a sparse covering of the barnacle Semibalanus balanoides and the limpet Patella vulgata. The mussel Mytilus edulis is confined to pits and crevices. A variety of winkles including Littorina littorea, Littorina saxatilis and the whelk Nucella lapillus are found beneath the seaweeds, whilst Littorina graze on the fucoid fronds. The calcareous tube-forming polychaete Spirorbis spirorbis may also occur epiphytically on the fronds. In areas of localised shelter the wrack Ascophyllum nodosum may occur, though never at high abundance. Damp cracks and crevices often contain patches of the red seaweed Mastocarpus stellatus and even the wrack Fucus serratus may be present. The crab Carcinus maenas may be present in pools or among the boulders.

Situation

This biotope usually occurs between the wrack Fucus spiralis (Fspi) and the F. serratus (Fserr) zones; both of these fucoids may be present in this biotope, though never at high abundance (typically less than Frequent). In some sheltered areas F. vesiculosus forms a narrow zone above the A. nodosum zone (Asc). Where freshwater runoff occurs on more gradually sloping shores F. vesiculosus may be replaced by the wrack Fucus ceranoides (Fcer).

Temporal variation

On some shores, particularly those which are moderately exposed to wave action, temporal fluctuations in the abundance of limpets, barnacles and fucoid seaweeds may occur. As a result, over a number of years, a single shore may cycle between the barnacle-P. vulgata dominated biotope (Sem.FvesR), through this mosaic (FvesB) to a F. vesiculosus-dominated biotope (Fves).

Characterising species

Similar biotopes or habitat types

LR.HLR.MusB.Sem.FvesR

Occurs on more exposed shores or on steep or vertical faces. Sparse F. vesiculosus is present (Occasional) and the density of S. balanoides and P. vulgata is high (Abundant). More species of red seaweeds are present, while the wracks Ascophyllum nodosum and Fucus serratus are absent.

LR.MLR.BF.FvesB

Occurs on more exposed shores on bedrock and large boulders. F. vesiculosus is dominating, though less abundant (Common) and there is a higher diversity of red seaweeds. S. balanoides, P. vulgata and N. lapillus occurs more frequently and at higher abundance.

Classification history of this biotope or habitat type