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Marine Habitat Classification


Description of biotope or habitat type

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   Phakellia ventilabrum and Axinellid sponges on deep, wave- exposed circalittoral rock


Habitat (physical) 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)
Substratum Bedrock
Zone Circalittoral - lower, Circalittoral - upper
Depth Band 20-30 m, 30-50 m
Other Features

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.

Distribution of habitat CR.HCR.DpSp.PhaAxi <I>Phakellia ventilabrum</I> and Axinellid sponges on deep, wave- exposed circalittoral rock

  • 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.

Description

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 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 ByErSp.Eun. The top shell Calliostoma zizyphinum is often recorded as present.

Situation

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.

Temporal variation

Axinella dissimilis tends to grow extremely slowly.

Characterising Species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Pachymatisma johnstonia 3 Occasional 81-100 %
Tethya aurantium 1 Occasional 61-80 %
Polymastia boletiformis 3 Frequent 81-100 %
Suberites carnosus 2 Occasional 61-80 %
Stelligera rigida 2 Occasional 61-80 %
Stelligera stuposa 3 Frequent 81-100 %
Cliona celata 4 Frequent 81-100 %
Axinella dissimilis 2 Occasional 81-100 %
Axinella infundibuliformis 4 Frequent 81-100 %
Phakellia ventilabrum 2 Frequent 61-80 %
Hemimycale columella 1 Occasional 61-80 %
Haliclona viscosa 3 Frequent 61-80 %
Dysidea fragilis 3 Occasional 81-100 %
Sertularella gayi 2 Occasional 61-80 %
Nemertesia antennina 2 Occasional 61-80 %
Nemertesia ramosa 1 Occasional 61-80 %
Alcyonium digitatum 3 Frequent 81-100 %
Alcyonium glomeratum 2 Frequent 81-100 %
Eunicella verrucosa 1 Occasional 41-60 %
Corynactis viridis 2 Frequent 41-60 %
Caryophyllia smithii 6 Frequent 81-100 %
Calliostoma zizyphinum 3 Occasional 81-100 %
Porella compressa 4 Frequent 81-100 %
Pentapora foliacea 2 Frequent 61-80 %
Parasmittina trispinosa 2 Frequent 41-60 %
Luidia ciliaris 2 Occasional 61-80 %
Henricia oculata 3 Occasional 81-100 %
Stichastrella rosea 1 Occasional 41-60 %
Marthasterias glacialis 2 Occasional 61-80 %
Echinus esculentus 3 Occasional 81-100 %
Holothuria forskali 4 Frequent 81-100 %
Aslia lefevrei 1 Occasional 41-60 %

Similar biotopes

CR.MCR.EcCr.CarSp.PenPcom
This biotope occurs under similar conditions as PhaAxi, although it tends to be found over a shallower depth range. Although high abundances of C. smithii are recorded in both these biotopes, CarSp.PenPcom has a less diverse sponge fauna than PhaAxi. The latter in particular is characterised by a diverse range of erect branching sponges. E. verrucosa is also occasionally found in PhaAxi.

CR.HCR.XFa.ByErSp.Sag
This biotope occurs on extremely exposed to moderately exposed coasts, subject to moderately strong tides. ByErSp.Sag also occurs over a shallower depth band. ByErSp.Sag has a more restricted range of sponges compared to PhaAxi. However, there is usually a more diverse range of hydroid and bryozoan 'turf-forming' species in ByErSp.Sag. Both biotopes occur mainly around the west coast of Ireland.

CR.HCR.XFa.ByErSp.Eun
This biotope occurs under similar wave-exposure conditions as PhaAxi, but is found in sites subject to moderately strong tidal streams. ByErSp.Eun is found much shallower than the deeper 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 PhaAxi. It is the absence of significant numbers of erect sponges that distinguishes this biotope from PhaAxi.

Biotope history

Classification Habitat code
97.06 CR.MCR.XFa.PhaAxi

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