Description of biotope or habitat type
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Solitary ascidians, including Ascidia mentula and Ciona intestinalis, with Antedon spp. on wave-sheltered circalittoral rock
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Sheltered, Very sheltered, Extremely sheltered |
| Tidal streams | Weak (>1 kn), Very weak (negligible) |
| Substratum | Bedrock, boulders |
| Zone | Circalittoral |
| Depth Band | 5-10 m, 10-20 m, 20-30 m, 30-50 m |
| Other Features | Often on vertical rock. |
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 occurs on circalittoral bedrock or boulder slopes in generally wave-sheltered conditions (often in sea lochs) with little tidal flow. It is frequently found on vertical or steeply-sloping rock. Apart from the large ascidians, Ascidia mentula and Ciona intestinalis, the rock surface usually has a rather sparse appearance. Scyphistomae larvae are often present on any vertical surfaces. Grazing by the sea urchin Echinus esculentus leaves only encrusting red algae (giving the bedrock/boulder substratum a pink appearance), cup corals Caryophyllia smithii and the keelworm Spirobranchus triqueter. There may be a few hydroid species present, such as Nemertesia spp. and Kirchenpaueria pinnata, occasional Alcyonium digitatum and occasional Metridium senile. Barnacles Balanus spp. and the colonial ascidian Clavelina lepadiformis also occasionally occur. At some sites, echinoderms such as the crinoid Antedon spp., the starfish Crossaster papposus and Asterias rubens and the brittlestar Ophiothrix fragilis (in low densities) may be found. The squat lobster Munida rugosa is likely to be found in crevices, under boulders, and the hermit crab Pagurus bernhardus may be observed moving around the rock surface. The brachiopod Novocrania anomala is frequently observed (especially where this biotope occurs shallower than NeoPro for example). The saddle oyster Pododesmus patelliformis may occasionally be seen attached to the rock/boulder face.
Situation
This biotope is typical of one found in sheltered sealochs. On slightly more wave and tide exposed sites, a transition to the more diverse AntAsH biotope will occur. Below AmenCio.Ant, you may find the NeoPro biotope (especially situated on the sills of sealochs).
Temporal variation
The abundance of C. intestinalis tends to fluctuate seasonally, so it may appear absent at a site at one time of year and then be present at other times, altering the visual appearance of the biotope. Other solitary ascidian species such as A. mentula and Ascidiella aspersa tend to be longer-lived (approximately 7 years and 3 years respectively).
Characterising species
| Taxon | Relative importance of taxon for defining this community (%) | Typical abundance - SACFOR scale | % of core records where taxon was recorded |
|---|---|---|---|
| Echinus esculentus | 12 | Occasional | 81-100% |
| Spirobranchus triqueter | 10 | Frequent | 61-80% |
| Ciona intestinalis | 9 | Frequent | 61-80% |
| Corallinaceae | 7 | Common | 41-60% |
| Ascidia mentula | 6 | Frequent | 41-60% |
| Asterias rubens | 6 | Occasional | 41-60% |
| Caryophyllia smithii | 5 | Occasional | 41-60% |
| Munida rugosa | 5 | Occasional | 41-60% |
| Antedon bifida | 4 | Occasional | 41-60% |
| Alcyonium digitatum | 2 | Occasional | 21-40% |
| Antedon petasus | 2 | Frequent | 21-40% |
| Clavelina lepadiformis | 2 | Occasional | 41-60% |
| Crossaster papposus | 2 | Occasional | 21-40% |
| Metridium senile | 2 | Occasional | 21-40% |
| Ophiothrix fragilis | 2 | Occasional | 21-40% |
| Pagurus bernhardus | 2 | Occasional | 21-40% |
| Balanus crenatus | 1 | Occasional | 21-40% |
| Kirchenpaueria pinnata | 1 | Occasional | 21-40% |
| Nemertesia antennina | 1 | Occasional | 21-40% |
| Novocrania anomala | 1 | Frequent | 21-40% |
| Pododesmus patelliformis | 1 | Frequent | 21-40% |
Similar biotopes or habitat types
CR.MCR.EcCr.FaAlCr
This biotope is found on more wave-exposed sites subject to moderately strong to weak tidal streams. They occur on similar substratum and appear similar due to their characteristically barren nature. CR.MCR.EcCr.FaAlCr tends to have a higher abundance of A. digitatum than CR.LCR.BrAs.AmenCio.Ant, while the latter instead has a diverse range of solitary ascidians. CR.LCR.BrAs.AmenCio.Ant also tends to appear more silty than CR.MCR.EcCr.FaAlCr.
