Chthamalus spp. on exposed upper eulittoral rock
|Within Vocab||Marine Habitat Classification for Britain and Ireland Version 97.06|
|Definition||Exposed to moderately exposed upper and mid eulittoral bedrock and boulders are characterised by dense barnacles, Chthamalus spp. and the limpet Patella vulgata. On the west coast Chthamalus spp. dominate the upper to mid eulittoral, often forming a distinct white band above a darker Semibalanus balanoides zone (BPat.Sem). This is because Chthamalus montagui is better adapted to resist desiccation and, therefore, extends further up the shore. There is much regional variation in the distribution and zonation of Chthamalus spp. In more northern latitudes, such as north-west Scotland, the abundance of Chthamalus is greater on more wave exposed shores. In the south-west Chthamalus spp. can be the dominant barnacle throughout the eulittoral zone. Patches of Lichina pygmaea may be prominent within the Chthamalus zone, especially in the south. Where this forms a distinct Lichina zone it should be recorded as BPat.Lic. Cracks and crevices in the rock provide a refuge for small mussels Mytilus edulis, winkles Littorina saxatilis and the dog whelk Nucella lapillus. Damp crevices are also frequently occupied by red algae, particularly Osmundea pinnatifida and encrusting coralline algae. With decreasing wave exposure Fucus vesiculosus is able to survive and this alga gradually replaces the barnacles and Patella biotope (see FvesB). On such moderately exposed shores BPat.Cht may occur on steep and vertical faces, while fucoids dominate the flatter areas. It should not be confused with more exposed shores characterised by Fucus vesiculosus f. linearis and Chthamalus spp. (BPat.Fvesl). In areas of soft rock (e.g. shales), the barnacles may be scarce or absent and the rock dominated by Patella. Chthamalus spp. are uncommonly abundant in the upper eulittoral zone in very sheltered sealochs in Argyll, West Scotland.|
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