Description of biotope or habitat type
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Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders
Physical habitat description
| Salinity | Full (30-35 ppt) |
|---|---|
| Wave exposure | Exposed, Moderately exposed |
| Tidal streams | Strong (3-6 kn), Moderately strong (1-3 kn) |
| Substratum | Bedrock; boulder |
| Zone | Circalittoral - lower, Circalittoral - upper |
| Depth Band | 5-10 m, 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 sub-biotope is typically found on the upper faces of exposed to moderately exposed, tide-swept, scoured, circalittoral bedrock or boulders. It most frequently occurs between 10-20 m water depth. The biotope is characteristically dominated by dense Flustra foliacea with a variety of slightly scour/silt-tolerant species forming a dense turf. This turf is primarily composed of bryozoans (Alcyonidium diaphanum, Bugulina flabellata, Crisularia plumosa, Bicellariella ciliata) and hydroids (Tubularia indivisa, Nemertesia antennina, Sertularia argentea, Hydrallmania falcata, Abietinaria abietina). Where space permits, barnacles such as Balanus crenatus may be found encrusting on the rock surface. There may also be occasional crusts formed by the polychaete Sabellaria spinulosa, especially where the rock is most influenced by sand. Anthozoans which may be observed include Urticina felina, Cylista elegans, whilst the soft coral Alcyonium digitatum may be recorded on the tops of boulders and bedrock ridges. A range of small solitary and colonial ascidians may be seen, including Polycarpa scuba, Dendrodoa grossularia, Molgula manhattensis, Botryllus schlosseri, Clavelina lepadiformis and polyclinids. Sponges found include Sycon ciliatum, Cliona celata, Amphilectus fucorum and Dysidea fragilis. Echinoderms such as Asterias rubens, Henricia oculata and Crossaster papposus may be seen on the rock surface. Other species found include the top shell Calliostoma zizyphinum, the crabs Cancer pagurus and Necora puber.
Situation
Above this variant, exposed kelp forest supporting Laminaria hyperborea is commonly found (LhypR). At locations where wave-exposure and/or tidal streams are less, this biotope may be replaced by Alcyonium digitatum and Securiflustra securifrons (FaAlCr.Sec). Where the substrata changes to a less stable mixed substrata, then this biotope will be replaced by the sub-biotope FluCoAs.X, with more `sediment' species such as Cerianthus lloydii and Chaetopterus variopedatus.
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 |
|---|---|---|---|
| Alcyonidium diaphanum | 6 | Frequent | 81-100% |
| Asterias rubens | 6 | Frequent | 81-100% |
| Flustra foliacea | 6 | Frequent | 81-100% |
| Balanus crenatus | 4 | Common | 61-80% |
| Urticina felina | 4 | Frequent | 81-100% |
| Alcyonium digitatum | 3 | Occasional | 61-80% |
| Bugulina flabellata | 3 | Occasional | 61-80% |
| Henricia | 3 | Occasional | 41-60% |
| Sycon ciliatum | 3 | Frequent | 61-80% |
| Crisularia plumosa | 2 | Frequent | 61-80% |
| Cancer pagurus | 2 | Occasional | 61-80% |
| Crossaster papposus | 2 | Occasional | 61-80% |
| Dendrodoa grossularia | 2 | Frequent | 41-60% |
| Hydrallmania falcata | 2 | Frequent | 61-80% |
| Molgula manhattensis | 2 | Frequent | 41-60% |
| Necora puber | 2 | Occasional | 61-80% |
| Nemertesia antennina | 2 | Frequent | 61-80% |
| Polycarpa scuba | 2 | Frequent | 41-60% |
| Sabellaria spinulosa | 2 | Frequent | 41-60% |
| Cylista elegans | 2 | Occasional | 61-80% |
| Sertularia argentea | 2 | Frequent | 61-80% |
| Abietinaria abietina | 1 | Occasional | 41-60% |
| Bicellariella ciliata | 1 | Occasional | 41-60% |
| Botryllus schlosseri | 1 | Occasional | 41-60% |
| Calliostoma zizyphinum | 1 | Occasional | 41-60% |
| Clavelina lepadiformis | 1 | Occasional | 41-60% |
| Cliona celata | 1 | Occasional | 61-80% |
| Dysidea fragilis | 1 | Occasional | 41-60% |
| Amphilectus fucorum | 1 | Frequent | 41-60% |
| Polyclinum aurantium | 1 | Frequent | 41-60% |
| Tubularia indivisa | 1 | Occasional | 41-60% |
Similar biotopes or habitat types
CR.HCR.XFa.FluCoAs.Paur
This variant occurs on moderately wave-exposed sites but subject to similar tidal streams as CR.HCR.XFa.FluCoAs.SmAs. Although both sub-biotopes are dominated by F. foliacea, CR.HCR.XFa.FluCoAs.SmAs has a much more diverse associated sponge fauna and lacks the abundant sheets of the colonial ascidian Polyclinum aurantium characteristic of CR.HCR.XFa.FluCoAs.Paur.
CR.HCR.XFa.FluCoAs.X
This variant occurs under slightly more wave-exposed conditions, subject to similar tidal streams, but is found on mixed substrata (boulders, cobbles, pebbles and gravel) whereas CR.HCR.XFa.FluCoAs.SmAs is found on bedrock and boulders. CR.HCR.XFa.FluCoAs.X does not tend to have such a diverse range of sponges, and species found on more mixed sediment tend to be more prevalent (C. lloydii, C. variopedatus and Mimachlamys varia).
CR.HCR.XFa.ByErSp.DysAct
This sub-biotope occurs under more wave-exposed conditions, with slightly stronger tides than CR.HCR.XFa.FluCoAs.SmAs. They both tend to have a thin layer of silt overlying them. Sponges, hydroids and bryozoans are present in both biotopes. Although F. foliacea is present in CR.HCR.XFa.ByErSp.DysAct, it is not present in the same abundance as in CR.HCR.XFa.FluCoAs.SmAs, where it forms dense aggregations on the bedrock and boulders. In addition, species such as Caryophyllia (Caryophyllia) smithii and Corynactis viridis are absent from CR.HCR.XFa.FluCoAs.SmAs.
