Description of Mixed turf of bryozoans and erect sponges with [Dysidea fragilis] and [Actinothoe sphyrodeta] on tide-swept wave-exposed circalittoral rock
This variant typically occurs on exposed and moderately wave-exposed bedrock and boulders subject to a variety of tidal regimes (from strong through to weak). It is found mainly in the 10-20m depth range and does not usually occur deeper than 30 m. It therefore often straddles the upper circalittoral and lower infralittoral. It often has a light covering of silt and sand may be in the vicinity. Sponges form a dominant part of this variant, although cover usually appears patchy, with no single species dominating. Species present include Dysidea fragilis, Pachymatisma johnstonia, Esperiopsis fucorum, Hemimycale columella, Cliona celata, Stelligera rigida, Polymastia boletiformis, Stelligera stuposa, Raspailia ramosa, Tethya aurantium, Polymastia mamillaris and Axinella dissimilis. Tufts of large hydroids such as Nemertesia antennina, frequently recorded on the tops of outcrops and boulders, stand out more clearly than the understorey of finer hydroid and bryozoan turf such as Aglaophenia pluma, Bugula flabellata, Bugula plumosa, crisiids, Cellaria sinuosa and Bugula turbinata. Other bryozoans such as Alcyonidium diaphanum and Flustra foliacea are also frequently recorded. Other more widespread species present include Asterias rubens, Actinothoe sphyrodeta, Balanus crenatus, Caryophyllia smithii, Corynactis viridis, Necora puber and Clavelina lepadiformis. This variant has been recorded off the south east coast of Ireland, the welsh coast and Lundy Island. Situation: This biotope is typically found on exposed coasts, with exposed kelp forest in the infralittoral zone, characterised by species such as Laminaria hyperborea and Saccorhiza polyschides. The A4.1312 variant is usually found below A4.1311, with similar geographic range.