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Marine Habitat Classification

Description of biotope or habitat type

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   Hiatella arctica and seaweeds on vertical limestone / chalk.

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Very exposed, Exposed, Moderately exposed
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Bedrock
Zone Infralittoral
Depth Band 0-5 m, 5-10 m, 10-20 m
Other Features Vertical limestone.

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 IR.MIR.KR.HiaSw <I>Hiatella arctica</I> and seaweeds on vertical limestone / chalk.

  • 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 is found in the infralittoral zone on moderately exposed vertical limestone/chalk surfaces in weak tidal streams, and has been recorded most frequently between 0-10m. This biotope is characterised by abundant Hiatella arctica and a rich sponge community including Cliona celata, Dysidea fragilis and Pachymatisma johnstonia. Other species that may be frequent in this biotope are the crab Necora puber, the sea squirt Clavelina lepadiformis, and the top shell Calliostoma zizyphinum, although these species are found in other vertical rock biotopes, however in lesser abundance.


Shallow rocky coasts with vertical limestone faces.

Temporal variation

No temporal data available

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Alcyonium digitatum 4 Abundant 81-100%
Clavelina lepadiformis 4 Frequent 81-100%
Cliona celata 4 Common 81-100%
Dysidea fragilis 4 Frequent 81-100%
Calliostoma zizyphinum 3 Frequent 81-100%
Cancer pagurus 3 Occasional 81-100%
Hiatella arctica 3 Abundant 61-80%
Necora puber 3 Frequent 81-100%
Hydrozoa 2 Common 41-60%
Polychaeta 2 Common 61-80%
Aslia lefevrei 2 Frequent 61-80%
Botryllus schlosseri 2 Frequent 61-80%
Bryozoa indet crusts 2 Common 61-80%
Bugula 2 Frequent 61-80%
Caryophyllia smithii 2 Frequent 61-80%
Cryptopleura ramosa 2 Common 61-80%
Morchellium argus 2 Frequent 61-80%
Pachymatisma johnstonia 2 Frequent 61-80%
Phyllophora crispa 2 Abundant 41-60%
Urticina felina 2 Frequent 61-80%
Maja squinado 2 Occasional 81-100%
Corallinaceae 1 Occasional 61-80%
Membranipora membranacea 1 Frequent 41-60%
Aplidium punctum 1 Occasional 61-80%
Asterias rubens 1 Occasional 61-80%
Balanus crenatus 1 Common 41-60%
Vertebrata byssoides 1 Common 41-60%
Corynactis viridis 1 Occasional 61-80%
Dercitus bucklandi 1 Frequent 61-80%
Didemnidae 1 Frequent 61-80%
Amphilectus fucorum 1 Frequent 41-60%
Halichondria panicea 1 Frequent 41-60%
Laminaria hyperborea 1 Common 41-60%
Mytilus edulis 1 Occasional 41-60%
Polycarpa scuba 1 Abundant 41-60%
Spirobranchus triqueter 1 Common 41-60%
Cylista elegans 1 Frequent 41-60%
Tethya aurantium 1 Frequent 61-80%

Similar biotopes or habitat types

Similar vertical limestone/chalk habitat, but lacks seaweed component.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) IMX.VsenMtru
1996 (6.95) IMX.VenMya

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