Description of biotope or habitat type
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Phakellia ventilabrum and Axinellid sponges on deep, wave- exposed circalittoral rock
Physical habitat description
|Salinity||Full (30-35 ppt)|
|Wave exposure||Extremely exposed, Very exposed, Exposed|
|Tidal streams||Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)|
|Zone||Circalittoral - lower, Circalittoral - upper|
|Depth Band||20-30 m, 30-50 m|
Download comparative physical and biological data. The comparative tables enable a rapid comparison of the species composition and principal physical characteristics between a given set of biotopes.
- Records used to define the biotope (core records)
- Other records assigned to this biotope, marked as 'certain'
- Other records assigned to this biotope, marked as 'uncertain'
- Predicted extent of the level 3 (for sublittoral rock & deep sea) or 4 (for sublittoral sediment) habitat
Point data based on records in the UK Marine Recorder Snapshot. Predicted habitat extent is from UKSeaMap.
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 (BrErSp) 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 montagui, 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 (Panningothuria) 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 ByErSp.Eun. The top shell Calliostoma zizyphinum is often recorded as present.
CarSp.PenPor probably occurs above PhaAxi 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 PhaAxi biotope to develop.
Axinella dissimilis tends to grow extremely slowly.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
|Holothuria (Panningothuria) forskali||4||Frequent||81-100%|
Similar biotopes or habitat types
CR.MCR.EcCr.CarSp.PenPcomThis biotope occurs under similar conditions as CR.HCR.DpSp.PhaAxi, although it tends to be found over a shallower depth range. Although high abundances of C. smithii are recorded in both these biotopes, CR.MCR.EcCr.CarSp.PenPcom has a less diverse sponge fauna than CR.HCR.DpSp.PhaAxi. The latter in particular is characterised by a diverse range of erect branching sponges. E. verrucosa is also occasionally found in CR.HCR.DpSp.PhaAxi.
CR.HCR.XFa.ByErSp.CylThis biotope occurs on extremely exposed to moderately exposed coasts, subject to moderately strong tides. CR.HCR.XFa.ByErSp.Cyl also occurs over a shallower depth band. CR.HCR.XFa.ByErSp.Cyl has a more restricted range of sponges compared to CR.HCR.DpSp.PhaAxi. However, there is usually a more diverse range of hydroid and bryozoan 'turf-forming' species in CR.HCR.XFa.ByErSp.Cyl. Both biotopes occur mainly around the west coast of Ireland.
CR.HCR.XFa.ByErSp.EunThis biotope occurs under similar wave-exposure conditions as CR.HCR.DpSp.PhaAxi, but is found in sites subject to moderately strong tidal streams. CR.HCR.XFa.ByErSp.Eun is found much shallower than the deeper CR.HCR.DpSp.PhaAxi, with a mean depth of 20m to 24m, although typically found on the same substratum. E. verrucosa is very abundant in this biotope, although it is still present in CR.HCR.DpSp.PhaAxi. It is the absence of significant numbers of erect sponges that distinguishes this biotope from CR.HCR.DpSp.PhaAxi.
Classification history of this biotope or habitat type