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Marine Habitat Classification

Description of biotope or habitat type

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   Circalittoral mussel beds on rock

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum Bedrock
Zone Circalittoral - upper, Circalittoral
Depth Band 5-10 m, 10-20 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.CMus Circalittoral mussel beds on 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 complex occurs on moderately wave-exposed upper circalittoral bedrock subject to strong or moderately strong tidal streams. This complex is characterised by dense aggregations of the mussels Mytilus edulis or Musculus discors carpeting the underlying substrata. Sponges that may be recorded in this complex are Scypha ciliata, Tethya aurantium, Pachymatisma johnstonia, Dysidea fragilis and Cliona celata. A sparse hydroid/bryozoan turf composed primarily of Nemertesia antennina, Alcyonidium diaphanum and Flustra foliacea is often recorded. Anemones present are Urticina felina and Sagartia elegans. Other species recorded are the crabs Cancer pagurus, Carcinus maenas and Necora puber, the starfish Crossaster papposus and Asterias rubens, and Alcyonium digitatum. In this upper circalittoral complex, algae species such as Dictyota dichotoma, Cryptopleura ramosa and Plocamium cartilagineum. Two biotopes have been identified: CMyt (M. edulis dominated) and Mdis (M. discors dominated).


No situation data available.

Temporal variation

No temporal variation data available.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Scypha ciliata 2 Occasional 21-40 %
Pachymatisma johnstonia 2 Occasional 21-40 %
Tethya aurantium 2 Occasional 21-40 %
Cliona celata 1 Rare 21-40 %
Dysidea fragilis 1 Occasional 21-40 %
Nemertesia antennina 2 Occasional 21-40 %
Alcyonium digitatum 1 Occasional 21-40 %
Urticina felina 6 Occasional 41-60 %
Sagartia elegans 3 Occasional 41-60 %
Balanus crenatus 2 Frequent 21-40 %
Cancer pagurus 4 Occasional 41-60 %
Necora puber 2 Rare 21-40 %
Carcinus maenas 1 Common 1-20 %
Mytilus edulis 18 Abundant 41-60 %
Musculus discors 13 Super abundant 41-60 %
Alcyonidium diaphanum 1 Frequent 21-40 %
Flustra foliacea 4 Occasional 41-60 %
Crossaster papposus 2 Occasional 21-40 %
Asterias rubens 15 Frequent 61-80 %
Plocamium cartilagineum 1 Occasional 21-40 %
Cryptopleura ramosa 1 Frequent 21-40 %
Dictyota dichotoma 1 Frequent 21-40 %

Similar biotopes or habitat types

Not applicable or unknown.

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