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Marine Habitat Classification

Description of biotope or habitat type

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   Sabellaria spinulosa, didemnids and other small ascidians on tide-swept moderately wave-exposed circalittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Moderately strong (1-3 kn)
Substratum Bedrock, boulders, cobbles
Zone Circalittoral - lower
Depth Band 10-20 m, 20-30 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.CSab.Sspi.As <I>Sabellaria spinulosa</I>, didemnids and other small ascidians on tide-swept moderately 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 tide-swept, moderately wave-exposed circalittoral bedrock, boulders and cobbles subject to slight sand-scour. It occurs predominantly in the lower circalittoral. This variant normally appears as a bedrock/boulder outcrop or reef with a dense crust of the polychaete Sabellaria spinulosa and a dense turf of didemnid ascidians and scour-tolerant bryozoans such as Flustra foliacea, Pentapora foliacea and Cellaria species. There may be discreet clumps of Alcyonium digitatum and sparse sponges such as Tethya aurantium and Phorbas fictitius. Patchy occurrences of the small ascidians Polycarpa scuba, Polycarpa pomaria and Distomus variolosus may be present on the tops of rocks and boulders whilst in crevices between, the anemone Urticina felina may be found. Species such as Asterias rubens, Crossaster papposus, the serpulid worm Salmacina dysteri and the anemone Cylista elegans are occasionally seen on the rock surface. This variant has been recorded from the Lleyn Peninsula, the Skerries and around Pembrokeshire in Wales.


No situation data available.

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
Sabellaria spinulosa 26 Common 81-100%
Didemnidae 21 Frequent 81-100%
Flustra foliacea 7 Occasional 61-80%
Alcyonium digitatum 6 Frequent 41-60%
Asterias rubens 6 Occasional 61-80%
Distomus variolosus 4 Frequent 41-60%
Pentapora foliacea 4 Occasional 41-60%
Polycarpa pomaria 4 Common 41-60%
Cellaria 2 Frequent 21-40%
Crossaster papposus 2 Occasional 21-40%
Phorbas fictitius 2 Occasional 21-40%
Polycarpa scuba 2 Common 21-40%
Salmacina dysteri 2 Occasional 21-40%
Tethya aurantium 2 Occasional 21-40%
Urticina felina 2 Occasional 21-40%
Cylista elegans 1 Occasional 21-40%

Similar biotopes or habitat types

This biotope is similar in that the polychaete tubeworm S. spinulosa is the prevalent species, however, it lacks the dense turf of colonial ascidians such as didemids and Polycarpa spp., and instead has more barnacles and a bryozoan turf.

This biotope is found on circalittoral mixed sediment, not rock or mixed substrata in the case of CR.MCR.CSab.Sspi.As.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) CR.MCR.CSab.Sspi

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