Fucus serratus, sponges and ascidians on tide-swept lower eulittoral rock

Description (English)

Sheltered to extremely sheltered lower eulittoral bedrock, boulders and cobbles that are subject to increased tidal water movement and characterised by the wrack Fucus serratus and a rich assemblage of filter-feeding fauna. This community is encouraged by the increased water movement. It includes species such as the sponges Halichondria panicea and Hymeniacidon perleve, which occur frequently on steep and overhanging faces. Underneath the F. serratus canopy is a diverse flora of foliose red seaweeds including Mastocarpus stellatus, Lomentaria articulata, Membranoptera alata and Chondrus crispus. The green seaweeds Cladophora spp., Enteromorpha intestinalis and Ulva lactuca and the wrack Ascophyllum nodosum are present though usually in small numbers. On the rock underneath the seaweed canopy, species such as the limpet Patella vulgata, the barnacles Semibalanus balanoides and Balanus crenatus and the whelk Nucella lapillus can be found though in lower abundance than higher up the shore. Also present on the rock are the tube-forming polychaetes Pomatoceros triqueter and spirorbids and more mobile species such as the winkles Littorina mariae and Littorina littorea, the top shell Gibbula cineraria and the crab Carcinus maenas. Lastly, several species of bryozoans are usually present including Electra pilosa and Alcyonidium gelatinosum, all competing for space with the hydroid Dynamena pumila, which can form dense populations on the F. serratus fronds.
Situation: Areas where increased tidal movement influences such a community are in the narrows and/or intertidal sills of Scottish sea lochs and the rias in south-west England. In the few cases where the rock is also subject to variable salinity, an impoverished community results and records should be classified as A1.326 rather than the present biotope.

Source: EUNIS habitat classification