Skip to Content

Marine Habitat Classification

Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   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 Sycon ciliatum, 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 Cylista 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
Mytilus edulis 18 Abundant 41-60%
Asterias rubens 15 Frequent 61-80%
Musculus discors 13 Super abundant 41-60%
Urticina felina 6 Occasional 41-60%
Cancer pagurus 4 Occasional 41-60%
Flustra foliacea 4 Occasional 41-60%
Cylista elegans 3 Occasional 41-60%
Balanus crenatus 2 Frequent 21-40%
Crossaster papposus 2 Occasional 21-40%
Necora puber 2 Rare 21-40%
Nemertesia antennina 2 Occasional 21-40%
Pachymatisma johnstonia 2 Occasional 21-40%
Sycon ciliatum 2 Occasional 21-40%
Tethya aurantium 2 Occasional 21-40%
Alcyonidium diaphanum 1 Frequent 21-40%
Alcyonium digitatum 1 Occasional 21-40%
Carcinus maenas 1 Common 1-20%
Cliona celata 1 Rare 21-40%
Cryptopleura ramosa 1 Frequent 21-40%
Dictyota dichotoma 1 Frequent 21-40%
Dysidea fragilis 1 Occasional 21-40%
Plocamium cartilagineum 1 Occasional 21-40%

Similar biotopes or habitat types

Not applicable or unknown.

Back to top