Description of Sparse sponges, [Nemertesia] spp., and [Alcyonidium diaphanum] on circalittoral mixed substrata
This biotope is found on moderately wave-exposed sand-scoured, circalittoral boulders, cobbles and pebbles that are subject to moderately strong tidal streams (referred to as lag-cobbles locally). It is characterised by sparse sponges and a diverse bryozoan and hydroid turf. The sparse sponge community is primarily composed of Dysidea fragilis and Scypha ciliata. The mixed faunal turf is composed of Nemertesia antennina, Nemertesia ramosa, Halecium halecinum, Sertularia argentea, Alcyonium digitatum, Bugula flabellata, Bugula turbinata, Bugula plumosa, Flustra foliacea, Cellepora pumicosa, Alcyonidium diaphanum, Cellaria fistulosa and crisiid bryozoans. The anemones Epizoanthus couchii, Sagartia elegans and Cerianthus lloydii may also be recorded. Echinoderms such as the starfish Asterias rubens, Crossaster papposus, Henricia oculata and the crinoid Antedon bifida. Other species present include the colonial ascidian Clavelina lepadiformis, the barnacle Balanus crenatus, the top shell Gibbula cineraria, the polychaete Pomatoceros triqueter, the ascidian Morchellium argus, Prosthecareus vittatus and the crab Cancer pagurus. It is distributed off Pen Llyn and over considerable areas of the Irish Sea.