Description of biotope or habitat type
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Alcyonium digitatum with dense Tubularia indivisa and anemones on strongly tide-swept circalittoral rock
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Extremely exposed, Very exposed, Exposed |
| Tidal streams | Very strong (>6 kn), Strong (3-6 kn), Moderately strong (1-3 kn) |
| Substratum | bedrock; boulders |
| Zone | Circalittoral - lower, Circalittoral - upper |
| Depth Band | 5-10 m, 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 exposed circalittoral bedrock and boulders in sounds, narrows and around tide-swept promontories in accelerated tidal streams. It is dominated by aggregations of dead man's fingers Alcyonium digitatum, and dense clumps or continuous cover of the robust hydroid Tubularia indivisa, particularly on prominent ledges and ridges. Anemones such as Cylista elegans, Urticina felina, Metridium senile, Actinothoe sphyrodeta and Corynactis virdis form a prominent component of the community. Occasionally, massive sponges such as Pachymatisma johnstonia and Amphilectus fucorum may be present. Encrusting species such as the polychaete Spirobranchus triqueter and the barnacle Balanus crenatus may be dotted around the rocks, and the top shell Calliostoma zizyphinum may also be observed. Clumps of the bryozoan Flustra foliacea are occasionally seen. The starfish Asterias rubens may be seen amongst a patchy turf of Crisia denticulata and the bryozoan Alcyonidium diaphanum. This variant may also be found on tideswept wrecks and other artificial sustratum.
Situation
Above this biotope, it is usual to find well-developed kelp forest in the upper infralittoral, dominated by Laminaria hyperborea (LhypR). In the lower infralittoral, it is usual to find a tide-swept turf of hydroids and red algae.
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 |
|---|---|---|---|
| Tubularia indivisa | 27 | Common | 81-100% |
| Alcyonium digitatum | 21 | Frequent | 81-100% |
| Asterias rubens | 7 | Occasional | 61-80% |
| Cylista elegans | 6 | Common | 61-80% |
| Corynactis viridis | 3 | Common | 21-40% |
| Pachymatisma johnstonia | 3 | Occasional | 41-60% |
| Urticina felina | 3 | Frequent | 41-60% |
| Alcyonidium diaphanum | 2 | Frequent | 21-40% |
| Calliostoma zizyphinum | 2 | Occasional | 41-60% |
| Amphilectus fucorum | 2 | Frequent | 21-40% |
| Flustra foliacea | 2 | Occasional | 41-60% |
| Metridium senile | 2 | Frequent | 21-40% |
| Spirobranchus triqueter | 2 | Frequent | 21-40% |
| Actinothoe sphyrodeta | 1 | Frequent | 21-40% |
| Balanus crenatus | 1 | Common | 21-40% |
| Crisia denticulata | 1 | Occasional | 21-40% |
Similar biotopes or habitat types
CR.HCR.FaT.CTub.CuSp
This biotope occurs on slightly more wave-sheltered sites than CR.HCR.FaT.CTub.Adig. However, they are both subject to generally similar, strong tidal streams. CR.HCR.FaT.CTub.CuSp also tends to be found slightly deeper. Although a similar suite of hydroid species are found in both biotopes, CR.HCR.FaT.CTub.CuSp has a more diverse range of sponges, ascidians, and turf-forming bryozoans such as Bugula spp. In addition, dense colonies of A. digitatum are found in CR.HCR.FaT.CTub.Adig.
CR.HCR.FaT.BalTub
This biotope tends to be found across a broader range of wave-exposures compared to Tub.Adig. However, they are both subject to similar tidal-streams. CR.HCR.FaT.BalTub also tends to be found on a wider range of substratum types compared to CR.HCR.FaT.CTub.Adig. CR.HCR.FaT.BalTub has a 'bare' appearance, dominated by T. indivisa and B. crenatus, whereas CR.HCR.FaT.CTub.Adig has a more diverse range of sponges, ascidians, and turf-forming bryozoans.Classification history of this biotope or habitat type
| Classification version | Code |
|---|---|
| 1997 (97.06) | CR.ECR.Alc.AlcTub |
Photos
