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Marine Habitat Classification

Description of biotope or habitat type

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   Brittlestars overlying coralline crusts, Parasmittina trispinosa and Caryophyllia smithii on wave-exposed circalittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed, Moderately exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Bedrock, boulders
Zone Circalittoral
Depth Band 10-20 m, 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.MCR.EcCr.CarSp.Bri Brittlestars overlying coralline crusts, <I>Parasmittina trispinosa</I> and <I>Caryophyllia smithii</I> on 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.


This variant is typically found on the upper faces of wave-exposed circalittoral bedrock or boulders subject to moderately strong to weak tidal streams, on open coasts. However, the depth at which the variant occurs means that wave action is not so severe on the seabed as to displace the dense mat of brittlestars that covers the seabed. Ophiothrix fragilis is usually the most dominant species in shallow water, with Ophiocomina nigra usually found amongst them, but sometimes becoming the dominant species in deeper water. Although brittlestar biotopes are typically species-poor, the underlying fauna in this variant is relatively diverse and resembles that of CarSp.PenPcom. Species such as the anemone Urticina felina, the cup coral Caryophyllia smithii, and the anemone Corynactis viridis may occasionally be present. There may also be sparse clumps of various hydroids including Halecium halecinum, Nemertesia antennina, Nemertesia ramosa, Sertularella gayi and Abietinaria abietina. Soft coral Alcyonium digitatum is occasionally present and there may be sparse specimens of the sponges Cliona celata and Polymastia boletiformis. In addition, various echinoderms such as Asterias rubens, Antedon bifida, Echinus esculentus, Henricia oculata, Marthasterias glacialis and Luidia ciliaris may be observed. The barnacle Balanus crenatus and the polychaete Spirobranchus triqueter may be seen attached to any available space on the bedrock and boulders not smothered by brittlestars. Bryozoan crusts such as Parasmittina trispinosa may also be present.


Wave-exposed seabed composed of bedrock ridges and/or boulder or cobble slope. Shallower than this biotope, the lower infralittoral kelp park is dominated by Laminaria hyperborea. A dense understorey may be present, containing Antedon spp., Phycodrys rubens and Plocamium cartilagineum.

Temporal variation

Not known.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Ophiothrix fragilis 14 Abundant 81-100%
Ophiocomina nigra 12 Common 81-100%
Asterias rubens 7 Occasional 81-100%
Alcyonium digitatum 5 Occasional 81-100%
Antedon bifida 4 Occasional 61-80%
Calliostoma zizyphinum 4 Occasional 81-100%
Henricia oculata 4 Occasional 81-100%
Urticina felina 4 Frequent 81-100%
Echinus esculentus 4 Occasional 61-80%
Caryophyllia smithii 3 Occasional 61-80%
Halecium halecinum 3 Occasional 61-80%
Marthasterias glacialis 3 Occasional 61-80%
Corallinaceae 2 Frequent 41-60%
Cliona celata 2 Occasional 61-80%
Corynactis viridis 2 Frequent 41-60%
Nemertesia antennina 2 Occasional 41-60%
Parasmittina trispinosa 2 Frequent 41-60%
Abietinaria abietina 1 Occasional 41-60%
Balanus crenatus 1 Frequent 21-40%
Luidia ciliaris 1 Occasional 41-60%
Nemertesia ramosa 1 Occasional 41-60%
Polymastia boletiformis 1 Occasional 41-60%
Spirobranchus triqueter 1 Occasional 41-60%
Sertularella gayi 1 Occasional 41-60%

Similar biotopes or habitat types

This biotope is found on slightly more wave-sheltered coasts, but subject to similar moderately strong to weak tidal streams. LR.LLR.FaAlc.Bri also tends to be fond on a more heterogeneous seabed, whereas CR.MCR.EcCr.CarSp.Bri is typically found on bedrock or boulders. Although they are both brittlestar biotopes, unlike CR.MCR.EcCr.CarSp.Bri, LR.LLR.FaAlc.Bri is devoid of any sponges, and is characterised by graze-resistant hydroids.

This biotope is found on sites with greatly reduced wave-exposures and tidal streams, compared to CR.MCR.EcCr.CarSp.Bri. As CR.LCR.BrAs.AmenCio.Bri is found in low-energy sites, it tends to be heavily silted compared to CR.MCR.EcCr.CarSp.Bri. Although both biotopes are dominated by brittlestars, CR.LCR.BrAs.AmenCio.Bri is more grazed and barren, and does not have such as diverse range of bryozoan crusts or hydroids (it does have a diverse range of anemones).

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