Description of biotope or habitat type
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Alcyonium digitatum with Securiflustra securifrons on tide-swept moderately wave-exposed circalittoral rock
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Exposed, Moderately exposed |
| Tidal streams | Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible) |
| Substratum | Bedrock |
| Zone | Circalittoral |
| Depth Band | 10-20 m, 20-30 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 upper and vertical faces of moderately wave-exposed circalittoral bedrock subject to moderately strong to weak tidal streams. The rock surface is dominated by Alcyonium digitatum and the bryozoan Securiflustra securifrons. The rock between these species appears fairly sparse and grazed, with expanses of encrusting red algae. The sea urchin Echinus esculentus is frequently seen, and in collaboration with the light attenuating effects of depth, is probably the principal reason for the lack of algal turf. Other species found include the hydroids Abietinaria abietina, Nemertesia antennina, Thuiaria thuja, the bryozoans Cellepora pumicosa, Parasmittina trispinosa, Flustra foliacea, Alcyonidium diaphanum and other bryozoan crusts. Encrusting species such as the polychaete Spirobranchus triqueter and the barnacle Balanus balanus are frequently observed. Other species present include Asterias rubens, Antedon bifida, Ophiura albida, Ophiothrix fragilis, Caryophyllia smithii, Urticina felina, Clavelina lepadiformis, Calliostoma zizphinium and Pandalus montagui.
Situation
Above this biotope, you tend to find exposed kelp forest and park (LhypR). There is a tendency for slight scouring to occur in this biotope. However, if this scour increases further, for example if water movement increases, mobilising more sand, this biotope may graduate into UrtScr. In more silty sites, there is a tendency for S. securifrons to be replaced by F. foliacea as the dominant bryozoan, turning the biotope into FaAlCr.Flu.
Temporal variation
Whilst the great majority of species in this variant are most likely present throughout the year, C. lepadiformis grows in spring and may show great variation in abundance from year to year.
Characterising species
| Taxon | Relative importance of taxon for defining this community (%) | Typical abundance - SACFOR scale | % of core records where taxon was recorded |
|---|---|---|---|
| Alcyonium digitatum | 14 | Common | 81-100% |
| Securiflustra securifrons | 12 | Frequent | 81-100% |
| Asterias rubens | 6 | Frequent | 81-100% |
| Spirobranchus triqueter | 5 | Frequent | 61-80% |
| Corallinaceae | 4 | Occasional | 61-80% |
| Echinus esculentus | 4 | Frequent | 61-80% |
| Abietinaria abietina | 3 | Frequent | 61-80% |
| Antedon bifida | 3 | Common | 41-60% |
| Caryophyllia smithii | 3 | Frequent | 41-60% |
| Ophiura albida | 3 | Frequent | 41-60% |
| Cellepora pumicosa | 2 | Occasional | 41-60% |
| Clavelina lepadiformis | 2 | Frequent | 41-60% |
| Nemertesia antennina | 2 | Frequent | 41-60% |
| Ophiothrix fragilis | 2 | Common | 41-60% |
| Parasmittina trispinosa | 2 | Occasional | 41-60% |
| Thuiaria thuja | 2 | Occasional | 41-60% |
| Urticina felina | 2 | Occasional | 61-80% |
| Porifera | 1 | Frequent | 41-60% |
| Alcyonidium diaphanum | 1 | Occasional | 21-40% |
| Balanus balanus | 1 | Occasional | 41-60% |
| Bryozoa | 1 | Frequent | 41-60% |
| Calliostoma zizyphinum | 1 | Occasional | 41-60% |
| Flustra foliacea | 1 | Occasional | 21-40% |
| Pandalus montagui | 1 | Frequent | 21-40% |
Similar biotopes or habitat types
CR.MCR.EcCr.FaAlCr.Adig
This biotope occurs on slightly more exposed sites subject to slightly stronger tidal streams. Although both biotopes are similarly quite clean and grazed, CR.MCR.EcCr.FaAlCr.Sec has a more diverse hydroid and bryozoan turf, with S. securifrons dominating.
CR.MCR.EcCr.FaAlCr.Flu
This biotope occurs under similar conditions as CR.MCR.EcCr.FaAlCr.Sec. CR.MCR.EcCr.FaAlCr is also found on a slightly more mixed substratum. F. foliacea, and to a lesser extent A. digitatum are the dominant species within this biotope whereas in CR.MCR.EcCr.FaAlCr.Sec, S. securifrons and A. digitatum dominate. CR.MCR.EcCr.FaAlCr also tends to have a more silty appearance whereas CR.MCR.EcCr.FaAlCr.Sec appears clean and grazed.Classification history of this biotope or habitat type
| Classification version | Code |
|---|---|
| 1997 (97.06) | CR.ECR.Alc.AlcSec |
