Description of biotope or habitat type
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Musculus discors beds on moderately exposed circalittoral rock
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Moderately exposed, Sheltered |
| Tidal streams | Moderately strong (1-3 kn) |
| Substratum | Bedrock, boulders, cobbles |
| Zone | Circalittoral - upper |
| Depth Band | 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.
- 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.
Description
This biotope typically occurs on the upper faces of moderately exposed, moderately tide-swept bedrock, boulders and cobbles in slightly silty conditions. The mussel Musculus discors occurs in dense mats and occasionally completely coats all available surfaces. There is also often a layer of pseudofaeces, forming a thick, silty matrix. A relatively diverse fauna of cushion and branching sponges is often present on rocky outcrops and other hard substratum that is free of mussels. These include Tethya aurantium, Sycon ciliatum, Pachymatisma johnstonia, Dysidea fragilis, Cliona celata and Stelligera stuposa. There may be isolated clumps of silt-tolerant bryozoans such as Flustra foliacea and Crisularia plumosa. Various species may be observed on top of the mussels, including Asterias rubens, Crossaster papposus and the brittlestar Ophiura albida. Occasional Alcyonium digitatum and clumps of the hydroid Nemertesia antennina are found attached to rocky outcrops and boulders whilst the anemone Urticina felina may be seen in crevices in the rock or on gravely patches between boulders. Colonial ascidians such as Clavelina lepadiformis and didemnids may occasionally be present. A wide range of seaweeds may be present, including Dictyota dichotoma, Plocamium cartliagineum, Dictyopteris polypodioides, Cryptopleura ramosa and Heterosiphonia plumosa. The crab Cancer pagurus may be observed in crevices. The majority of the records for this biotope are from the Lleyn Peninsula.
Situation
No situation data available.
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 |
|---|---|---|---|
| Musculus discors | 30 | Super abundant | 81-100% |
| Asterias rubens | 7 | Frequent | 61-80% |
| Flustra foliacea | 5 | Occasional | 61-80% |
| Tethya aurantium | 5 | Occasional | 61-80% |
| Crossaster papposus | 4 | Occasional | 61-80% |
| Sycon ciliatum | 4 | Occasional | 61-80% |
| Dictyota dichotoma | 3 | Frequent | 41-60% |
| Alcyonium digitatum | 2 | Occasional | 41-60% |
| Crisularia plumosa | 2 | Frequent | 41-60% |
| Cancer pagurus | 2 | Occasional | 41-60% |
| Clavelina lepadiformis | 2 | Occasional | 41-60% |
| Cliona celata | 2 | Rare | 41-60% |
| Dysidea fragilis | 2 | Occasional | 41-60% |
| Pachymatisma johnstonia | 2 | Occasional | 41-60% |
| Plocamium cartilagineum | 2 | Occasional | 41-60% |
| Urticina felina | 2 | Occasional | 41-60% |
| Cryptopleura ramosa | 1 | Occasional | 21-40% |
| Dictyopteris polypodioides | 1 | Occasional | 41-60% |
| Didemnidae | 1 | Occasional | 21-40% |
| Heterosiphonia plumosa | 1 | Occasional | 21-40% |
| Nemertesia antennina | 1 | Occasional | 41-60% |
| Ophiura albida | 1 | Frequent | 21-40% |
| Stelligera stuposa | 1 | Occasional | 41-60% |
Similar biotopes or habitat types