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Marine Habitat Classification

Description of biotope or habitat type

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   Caryophyllia smithii, Swiftia pallida and large solitary ascidians on exposed or moderately exposed circalittoral rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Extremely exposed, Very exposed, Exposed, Moderately exposed, Sheltered
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Bedrock; boulder
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.CarSwi.LgAs <I>Caryophyllia smithii</I>, <I>Swiftia pallida</I> and large solitary ascidians on exposed or moderately 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 typically occurs on exposed to moderately wave-exposed, circalittoral bedrock and boulders rock subject to mainly weak tidal streams and has a thin layer of silt present. It is found predominantly from 10-30m water depth. From afar, this biotope is mostly distinguished by the frequently occurring seafan Swiftia pallida, encrusting red algae and the abundant cup coral Caryophyllia smithii. This biotope has quite an impoverished appearance, compared with SwiLgAs which has a strong sponge component. Other species present are typically in low abundance. Echinoderms such as Echinus esculentus, Antedon bifida, Antedon petasus, Leptometra celtica, Marthasterias glacialis, Luidia ciliaris and Asterias rubens may be recorded. Large hydroids such as Nemertesia antennina and Nemertesia ramosa may occasionally be seen in isolated clumps on the tops of boulders and rocky outcrops. The anthozoan Parazoanthus anguicomus may be recorded. Bryozoans such as Parasmittina trispinosa and Porella compressa are occasionally observed. The polychaete Spirobranchus triqueter may be observed encrusting the sides of rocks and boulders while occasional Alcyonium digitatum may also be seen. A small suite of large ascidians may be present, including Ascidia mentula, Clavelina lepadiformis, Ciona intestinalis, Diazona violacea and Ascidia virginea. Sponges are typically absent from this biotope, although Cliona celata may be recorded occasionally. The top shell Steromphala cineraria is usually present. Under boulders and overhangs, the squat lobster Munida rugosa can usually be seen hiding. All these records are from the west coast of Scotland (East coast of Lewis /Outer Hebrides).


Above this biotope in the infralittoral zone, sheltered kelp forests are usually found, with species such as Laminaria hyperborea, Saccharina latissima and Sacchoriza polyschides. This biotope is found on bedrock and boulders, which may either be protruding from the surrounding sediment, or the sediment may be in a separate zone below the bedrock. These sediments may either be deep mud (with species such as Pachycerianthus and Nephrops ) on the sheltered sites or slightly coarser sediments (with Pennatula and Virgularia) on slightly more exposed sites.

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
Caryophyllia smithii 22 Abundant 81-100%
Swiftia pallida 12 Frequent 81-100%
Corallinaceae 7 Abundant 41-60%
Echinus esculentus 6 Frequent 61-80%
Parasmittina trispinosa 5 Occasional 61-80%
Ascidia mentula 4 Occasional 61-80%
Munida rugosa 4 Occasional 61-80%
Nemertesia antennina 4 Occasional 61-80%
Antedon bifida 3 Occasional 41-60%
Antedon petasus 3 Frequent 41-60%
Marthasterias glacialis 2 Occasional 41-60%
Nemertesia ramosa 2 Occasional 41-60%
Spirobranchus triqueter 2 Occasional 41-60%
Alcyonium digitatum 1 Occasional 41-60%
Ascidia virginea 1 Occasional 41-60%
Asterias rubens 1 Occasional 41-60%
Ciona intestinalis 1 Occasional 41-60%
Clavelina lepadiformis 1 Occasional 41-60%
Cliona celata 1 Occasional 41-60%
Diazona violacea 1 Occasional 41-60%
Steromphala cineraria 1 Occasional 21-40%
Luidia ciliaris 1 Rare 41-60%
Porella compressa 1 Rare 41-60%

Similar biotopes or habitat types

This biotope occurs in slightly more tide-swept sites than CR.MCR.EcCr.CarSwi.LgAs. They both occur across similar depth bands. CR.HCR.XFa.SwiLgAs appears a lot more biologically diverse, with a greater range of sponges, hydroids, bryozoans and ascidians, although this difference may possibly be due to poor data.

This biotope predominantly occurs in the sheltered end of the wave-exposure spectrum, subject to only weak tidal streams. It is typically found across similar depth bands as CR.MCR.EcCr.CarSwi.LgAs. This heavily silted biotope is characterised by Swiftia pallida, Alcyonium glomeratum, Isozoanthus sulcatus and the prominent Holothuria (Panningothuria) forskali. This biotope is only present around the coast of Ireland.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) CR.MCR.XFa.ErSSwi


CR.MCR.ECCR.CarSwi.LgAs Caryophyllia (Caryophyllia) smithii, Swiftia pallida and large solitary ascidians on exposed or moderately exposed circalittoral rock, Dunstaffnage, Lynn of Lorne. ANON© JNCC
CR.MCR.ECCR.CarSwi.LgAs Caryophyllia (Caryophyllia) smithii, Swiftia pallida and large solitary ascidians on exposed or moderately exposed circalittoral rock, Dunstaffnage, Lynn of Lorne. ANON© JNCC

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