Description of [Semibalanus balanoides] on exposed to moderately exposed or vertical sheltered eulittoral rock
Exposed to moderately exposed mid to upper eulittoral bedrock and large boulders characterised by dense barnacles Semibalanus balanoides and the limpet Patella vulgata. The community has a relatively low diversity of species though occasional cracks and crevices in the rock can provide a refuge for small individuals of the mussel Mytilus edulis, the winkle Littorina saxatilis and the whelk Nucella lapillus. Seaweeds are usually not found in high numbers though fissures and crevices in the bedrock can hold a sparse algal community including the green seaweed Enteromorpha intestinalis. On some shores the olive green lichen Verrucaria mucosa can be present in some abundance (Frequent). Three variants have been described: A S. balanoides and P. vulgata dominated community on bedrock (A1.1131); S. balanoides and sparse Fucus vesioculosus and red seaweeds (A1.1132); and barnacles and L. littorea eulittoral boulders and cobbles (A1.1133). Situation: On very exposed to exposed shores Chthamalus spp. (see A1.112 and subunits for geographical variation) often forms a distinct white band above a darker band of S. balanoides in the mid eulittoral zone. Alternatively, the black lichen Verrucaria maura dominated biotopes (B3.1131 or B3.1132) may be found above A1.113. In the lower eulittoral and the sublittoral fringe a community dominated by the wrack Himanthalia elongata and various red seaweeds such as Corallina officinalis, Mastocarpus stellatus and Osmundea pinnatifida (A1.123; A1 122; A1.126) often occurs. A1.113 may also occur on steep and vertical faces on more sheltered shores, while fucoids dominate the flatter areas (A1.213; A1.1132). Temporal variation: Periods with little scour or calmer weather can allow a seaweed community to develop, creating a more diverse biotope (i.e. A1.313 or A1.213). This is a dynamic process, which will change individual sites over time. More information is required to determine the exact nature of this process.