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4 results for 'CR.HCR.XFa.ByErSp'

   CR.HCR.XFa.ByErSp  Bryozoan turf and erect sponges on tide-swept circalittoral rock

This biotope is typically found on wave-exposed circalittoral bedrock or boulders subject to tidal streams ranging from moderately strong to strong. It often has a thin layer of silt covering the seabed, and is characterised by a bryozoan/hydroid turf with erect sponges. Typical bryozoans to be found include crisiids, Alcyonidium diaphanum, Flustra foliacea, Pentapora foliacea, Crisularia plumosa and Bugulina flabellata, while typical hydroids include Nemertesia antennina, Nemertesia ramosa and Halecium halecinum. The soft coral Alcyonium digitatum is frequently recorded on the tops of boulders and rocky outcrops. Characteristic erect sponges include Raspailia ramosa, Stelligera stuposa and Stelligera montagui; other sponges present include Cliona celata, Dysidea fragilis, Pachymatisma johnstonia, Polymastia boletiformis, Hemimycale columella, Amphilectus fucorum, Polymastia mamillaris and Tethya aurantium. Other species present include Caryophylia smithii, Actinothoe sphyrodeta, Corynactis viridis, Urticina felina, Balanus crenatus, Asterias rubens, Marthasterias glacialis, Henricia oculata, Echinus esculentus, Clavelina lepadiformis, Calliostoma zizyphinum and Necora puber. Three variants of this biotope have been described, but all are characterised by a bryozoan turf with erect sponges. ByErSp.Eun is found primarily on circalittoral bedrock and is dominated by the seafan Eunicella verrucosa. ByErSp.DysAct is found under slightly stronger tide-swept conditions, and is characterised particularly by the sponge D. fragilis and the anemone A. sphyrodeta. Finally ByErSp.Sag is characterised by the anemone Cylista elegans.

   CR.HCR.XFa.ByErSp.Cyl  Mixed turf of bryozoans and erect sponges with Cylista elegans on tide-swept ciraclittoral rock

This variant is typically found on wave-exposed circalittoral bedrock and boulders, on steep slopes and upper faces in moderate tidal streams. This species-rich biotope is characterised by a dense sponge, hydroid and bryozoan turf and frequent Alcyonium digitatum. There are frequently large growths of Cliona celata and Pachymatisma johnstonia. Other species present in this diverse sponge community include Polymastia boletiformis, Haliclona viscosa, Polymastia mamilliaris, Sycon ciliatum, Hemimycale columella and Dysidea fragilis. Axinellid sponges such as Stelligera stuposa and Raspailia ramosa may be present in low abundance, and are usually more abundant in deeper water. A dense hydroid turf forms a significant part of this biotope, with tufts of large hydroids such as Nemertesia antennina and Nemertesia ramosa frequently recorded. Other hydroid turf component species include Halecium halecinum, Aglaophenia tubulifera and Abietinaria abietina. Anemones are also well represented, with species such as Urticina felina, Cylista elegans and Metridium senile recorded. The cup coral Caryophyllia smithii and the anemone Corynactis viridis are also frequently seen. The bryozoan turf is composed predominantly of Alcyonidium diaphanum and Flustra foliacea, whilst crustose species such as Parasmittina trispinosa contribute to a lesser extent. The delicate Crisularia plumosa may also be present. There is a significant echinoderm component in this biotope. Species such as the starfish Asterias rubens, Henricia oculata, Marthasterias glacialis and Luidia ciliaris, the sea urchin Echinus esculentus and the crinoid Antedon bifida are all regularly recorded. Other species which may be observed include the top shell Calliostoma zizyphinium, the colonial ascidian Clavelina lepadiformis and the barnacle Balanus crenatus. The crab Cancer pagurus is typically found under boulders. This variant has been recorded from from various sites including Pembrokeshire, the Calf of Man and the west coast of Ireland.

   CR.HCR.XFa.ByErSp.Eun  Eunicella verrucosa and Pentapora foliacea on wave-exposed circalittoral rock

This variant typically occurs on wave-exposed, steep, circalittoral bedrock, boulder slopes and outcrops, subject to varying tidal streams. This silty variant contains a diverse faunal community, dominated by the seafan Eunicella verrucosa, the bryozoan Pentapora foliacea and the cup coral Caryophyllia smithii. There are frequently numerous Alcyonium digitatum, and these may become locally abundant under more tide-swept conditions. Alcyonium glomeratum may also be present. A diverse sponge community is usually present, including numerous erect sponges; species present include Cliona celata, Raspailia ramosa, Raspailia (Clathriodendron) hispida, Axinella dissimilis, Stelligera stuposa, Dysidea fragilis and Polymastia boletiformis. Homaxinella subdola may be present in the south west. A hydroid/bryozoan turf may develop in the understorey of this rich sponge assemblage, with species such as Nemertesia antennina, Nemertesia ramosa, crisiids, Alcyonidium diaphanum and Crisularia plumosa. The sea cucumber Holothuria (Panningothuria) forskali may be locally abundant, feeding on the silty deposits on the rock surface. Other echinoderms encountered include the starfish Marthasterias glacialis and the urchin Echinus esculentus. Other fauna includes aggregations of colonial ascidians Clavelina lepadiformis and Stolonica socialis. Anemones such as Actinothoe sphyrodeta and Parazoanthus axinellae may be seen dotted across the rock surface. This biotope is present in south west England and Wales.

   CR.HCR.XFa.ByErSp.DysAct  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, Amphilectus fucorum, Hemimycale columella, Cliona celata, Stelligera montagui, 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, Bugulina flabellata, Crisularia plumosa, crisiids, Cellaria sinuosa and Bugulina 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.
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