Large solitary ascidians and erect sponges on wave-sheltered circalittoral rock

Description (English)

A4.312 is characteristic of the wave-sheltered conditions found in the Kenmare River on the west coast of Ireland. This biotope is typically found on silty circalittoral bedrock and boulders in wave-sheltered channels subject to varying amounts of tidal flow. These fully marine inlets and channels have steep, often vertical sides with small terraces or ledges. This biotope, characterised by erect sponges and large solitary ascidians, appears to be biologically diverse. A diverse ascidian fauna is generally present, including Ascidia mentula, Aplidium punctum, Corella parallelogramma, Ascidia virginea, Botryllus schlosseri, Clavelina lepadiformis and Ciona intestinalis. An equally diverse sponge fauna, with massive erect sponges particularly noticeable, compliments these species. Dominant species include Esperiopsis fucorum, Dysidea fragilis, Tethya aurantium, Polymastia boletiformis, Raspailia ramosa, Stelligera stuposa, Polymastia mamilliaris and Pachymatisma johnstonia. Other sponges present are Suberites carnosus, Haliclona fistulosa, Stelligera rigida, Mycale rotalis, Haliclona simulans, Iophon hyndmani and Hemimycale columella. Various sponge crusts may also be present but in most cases in lower abundances. Other significant components of the community include the cup coral Caryophyllia smithii and various echinoderms, including the sea urchin Echinus esculentus and the starfish Henricia oculata and Marthasterias glacialis. Small isolated clumps of Nemertesia antennina and individual Alcyonium digitatum may be seen, whilst the top shell Calliostoma zizyphinum may also be present. At present, there are relatively few records in this biotope, as it is only reported from around the south-western coast of Ireland, where sponge diversity is very high.
Situation: Due to the sheltered nature of the biotope, this unit is usually situated on bedrock/boulder outcrops associated with mud slopes and plains. Typical species found within these circalittoral muds include the seapen Virgularia mirablis and the anemone Pachycerianthus multiplicatus. In the infralittoral zone, sheltered kelp biotopes such as A5.521 with Laminaria saccharina occur frequently. In areas where there is a slightly stronger tidal-stream, the circalittoral muddy plains become more muddy gravel plains and slopes. Typical species found within these habitats include the anemones Mesacmaea mitchellii and Aureliana heterocera. When tidal-streams becomes negligible, but with similar wave-sheltered conditions, you tend to find A4.2111 biotopes occurring, especially in the same geographical location (around south-west/west Ireland) as A4.312.

Source: EUNIS habitat classification