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Marine Habitat Classification

Description of biotope or habitat type

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   Solitary ascidians, including Ascidia mentula and Ciona intestinalis, on wave-sheltered circalittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed, Sheltered, Very sheltered
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Bedrock, boulders, cobbles
Zone Circalittoral
Depth Band 5-10 m, 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.LCR.BrAs.AmenCio Solitary ascidians, including <I>Ascidia mentula</I> and <I>Ciona intestinalis</I>, on wave-sheltered 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 biotope predominantly occurs on the upper faces of wave-sheltered (often sealochs) circalittoral bedrock, boulder and cobble slopes with little tidal flow. Apart from the solitary ascidians Ciona intestinalis and Ascidia mentula, this biotope has a rather barren, pink appearance (due to the encrusting red algae), possibly due to grazing pressure from the sea urchin Echinus esculentus. Other organisms found encrusting the rocky surface include the polychaete Spirobranchus triqueter and the cup coral Caryophyllia smithii. Other species occasionally encountered include Alcyonium digitatum, Asterias rubens, Pagurus berhardus, Crossaster papposus, Antedon bifida and Metridium senile. Crustaceans such as Munida rugosa and Cancer pagurus may be recorded in crevices. Two variants of this biotope exist: AmenCio.Ant and AmenCio.Bri. AmenCio.Bri occurs where is a dense carpet of brittlestars which sometimes completely cover the rocky substratum. Species present include Ophiothrix fragilis, Ophiocomina nigra and Ophiura albida.


No situation data available.

Temporal variation

The abundance of C. intestinalis tends to fluctuate seasonally, so it may appear absent at a site at one time of year and then be present at other times, altering the visual appearance of the biotope. Other solitary ascidian species such as A. mentula and Ascidiella aspersa tend to be longer-lived (approximately 7 years and 3 years, respectively).

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Ophiothrix fragilis 15 Abundant 61-80%
Ophiocomina nigra 10 Common 41-60%
Echinus esculentus 10 Occasional 61-80%
Corallinaceae 8 Common 41-60%
Spirobranchus triqueter 7 Frequent 41-60%
Asterias rubens 6 Occasional 61-80%
Ciona intestinalis 4 Occasional 41-60%
Pagurus bernhardus 4 Occasional 41-60%
Munida rugosa 3 Occasional 21-40%
Ophiura albida 3 Occasional 21-40%
Alcyonium digitatum 2 Occasional 21-40%
Ascidia mentula 2 Occasional 21-40%
Crossaster papposus 2 Occasional 41-60%
Antedon bifida 1 Occasional 21-40%
Cancer pagurus 1 Rare 21-40%
Caryophyllia smithii 1 Occasional 21-40%
Metridium senile 1 Occasional 21-40%

Similar biotopes or habitat types

Not applicable or unknown.

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