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  4. MD1-211 - Phakellia ventilabrum et éponges axinellidées sur roche du circalittoral du large exposée aux vagues
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MD1-211 - Phakellia ventilabrum et éponges axinellidées sur roche du circalittoral du large exposée aux vagues

Phakellia ventilabrum and axinellid sponges on wave-exposed offshore circalittoral rock

Classification des habitats EUNIS 2022

Descriptif de l'habitat

This biotope typically occurs on the upper faces of deep (commonly below 30m depth), wave-exposed circalittoral rock subject to negligible tidal streams. Although it occurs in exposed and very exposed conditions, at such depth, the turbulent wave action appears to have a much-attenuated effect on the fauna compared with shallower depths. As the majority of records are from depths between 30-50+ m, slightly deeper than the depths of most surveys, it is possible that this biotope is more widespread than the available dataset indicates. The sponge component of this biotope is the most striking feature, with similar species to the bryozoan and erect sponge biotope complex (unit MC1-213) although in this case, the sponges Phakellia ventilabrum, Axinella infundibuliformis, Axinella dissimilis and Stelligera stuposa dominate. Other sponge species frequently found on exposed rocky coasts are also present in low to moderate abundance. These include Cliona celata, Polymastia boletiformis, Haliclona viscosa, Pachymatisma johnstonia, Dysidea fragilis, Suberites carnosus, Stelligera rigida, Hemimycale columella and Tethya aurantium. The cup coral Caryophyllia smithii and the anemone Corynactis virdis may be locally abundant in some areas, along with the holothurian Holothuria forskali. The soft corals Alcyonium digitatum and Alcyonium glomeratum are frequently observed. The bryozoans Pentapora foliacea and Porella compressa are also more frequently found in this deep-water biotope. Bryozoan crusts such as Parasmittina trispinosa are also occasionally recorded. Isolated clumps of large hydroids such as Nemertesia antennina, Nemertesia ramosa and Sertularella gayi may be seen on the tops of boulders and rocky outcrops. Large echinoderms such as Echinus esculentus, Luidia ciliaris, Marthasterias glacialis, Strichastrella rosea, Henricia oculata and Aslia lefevrei may also be present. The seafan Eunicella verucosa may be locally common but to a lesser extent than in unit MC1-2131. The top shell Calliostoma zizyphinum is often recorded as present.
Situation: Unit MC1-2222 probably occurs above unit MD1-211 in shallower water where the exposure of the coast ensures that there is more water mixing due to wave action. Deeper down, this effect is attenuated, allowing MD1-211 biotope to develop.
Temporal variation: Axinella dissimilis tends to grow extremely slowly.

Bibliography

European Topic Centre on Biological Diversity 2022. EUNIS marine habitat classification 2022 including crosswalks. Table Excel. (Source)