Description of biotope or habitat type
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Alcyonium digitatum, Spirobranchus triqueter, algal and bryozoan crusts on wave-exposed circalittoral rock
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Extremely exposed, Very exposed, Exposed, Moderately exposed |
| Tidal streams | Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn) |
| Substratum | Bedrock, boulders |
| Zone | Circalittoral |
| Depth Band | 5-10 m, 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.
- 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 variant is typically found on the vertical, steep and upper faces of wave-exposed circalittoral bedrock or boulders subject to varying amounts of current. The variant has a very grazed, sparse appearance, dominated only by the presence of Alcyonium digitatum and large expanses of encrusting red alage and bryozoan crusts particularly (Parasmittina trispinosa). The sparse appearance can be attributed to the frequently observed sea urchin Echinus esculentus. The polychaete Spirobranchus triqueter can be locally abundant, and may in some cases cover far more rock surface than A. digitatum, especially on vertical faces. Clumps of robust hydroids such as Abietinaria abietina occur occasionally. Other species present include the echinoderms Asterias rubens, Henricia sanguinolenta, Ophiothrix fragilis, the anemone Urticina felina, Calliostoma zizyphinum and Cancer pagurus.
Situation
Shallower than this biotope, dense kelp forest is typically found, containing species such as Laminaria hyperborea and Alaria esculentus. Occasionally, this biotope may be found on rocky outcrops surrounding by coarse sand. With this increased scour, MCR.UrtScr may develop at the rock/sand interface. Below this biotope, coarse sediments, muddy gravel and sand are typically recorded.
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 |
|---|---|---|---|
| Alcyonium digitatum | 22 | Abundant | 81-100% |
| Spirobranchus triqueter | 17 | Common | 81-100% |
| Echinus esculentus | 13 | Frequent | 81-100% |
| Corallinaceae | 12 | Common | 61-80% |
| Asterias rubens | 6 | Occasional | 61-80% |
| Urticina felina | 3 | Occasional | 41-60% |
| Abietinaria abietina | 2 | Occasional | 41-60% |
| Calliostoma zizyphinum | 2 | Occasional | 41-60% |
| Henricia | 2 | Occasional | 21-40% |
| Ophiothrix fragilis | 2 | Occasional | 41-60% |
| Parasmittina trispinosa | 2 | Occasional | 41-60% |
| Cancer pagurus | 1 | Rare | 41-60% |
| Rhodophyta | 1 | Frequent | 21-40% |
Similar biotopes or habitat types
CR.MCR.EcCr.CarSp.PenPcom
This biotope occurs at slightly more exposed, deeper sites with weaker tidal streams. However, they are both found on similar substratum. CR.MCR.EcCr.FaAlCr.Adig has a much less diverse, impoverished fauna than CR.MCR.EcCr.CarSp.PenPcom possibly due to grazing pressure from E. esculentus. CR.MCR.EcCr.CarSp.PenPcom has a more diverse range of sponges, hydroids and bryozoans.
CR.MCR.EcCr.FaAlCr.Sec
This biotope is found under slightly less exposed conditions, subject to weaker tidal streams. CR.MCR.EcCr.FaAlCr.Sec is also found at slightly shallower water depths than CR.MCR.EcCr.FaAlCr.Adig. Although both biotopes are similarly quite clean and grazed, CR.MCR.EcCr.FaAlCr.Sec has a more diverse hydroid and bryozoan turf, with Securiflustra securifrons dominating.
CR.HCR.XFa.CvirCri
This biotope is found under similar conditions as CR.MCR.EcCr.FaAlCr.Adig. Like CR.MCR.EcCr.FaAlCr.Adig, this biotope has dense A. digitatum. However, CR.HCR.XFa.CvirCri has a diverse sponge community.
CR.HCR.FaT.CTub.Adig
This biotope is found on extremely wave-exposed, extremely tide-swept bedrock or boulders. This biotope is similarly species poor, but is characterised by Tubularia indivisa.Classification history of this biotope or habitat type
| Classification version | Code |
|---|---|
| 2015 (15.03) | CR.MCR.EcCr.FaAlCr.Adig |
| 1997 (97.06) | CR.ECR.Alc.AlcC |
Photos
