Description of [Alcyonium digitatum] with dense [Tubularia indivisa] and anemones on strongly tide-swept circalittoral rock
This variant is typically found on exposed circalittoral bedrock and boulders in sounds, narrows and around tide-swept promontories in accelerated tidal streams. It is dominated by aggregations of dead man's fingers Alcyonium digitatum, and dense clumps or continuous cover of the robust hydroid Tubularia indivisa, particularly on prominent ledges and ridges. Anemones such as Sagartia elegans, Urticina felina, Metridium senile, Actinothoe sphyrodeta and Corynactis virdis form a prominent component of the community. Occasionally, massive sponges such as Pachymatisma johnstonia and Esperiopsis fucorum may be present. Encrusting species such as the polychaete Pomatoceros triqueter and the barnacle Balanus crenatus may be dotted around the rocks, and the top shell Calliostoma zizyphinum may also be observed. Clumps of the bryozoan Flustra foliacea are occasionally seen. The starfish Asterias rubens may be seen amongst a patchy turf of Crisia denticulata and the bryozoan Alcyonidium diaphanum. This variant may also be found on tideswept wrecks and other artificial sustratum. Situation: Above this biotope, it is usual to find well-developed kelp forest in the upper infralittoral, dominated by Laminaria hyperborea (unit A3.115). In the lower infralittoral, it is usual to find a tide-swept turf of hydroids and red algae.