Description of biotope or habitat type
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Flustra foliacea and colonial ascidians on tide-swept exposed circalittoral mixed substrata
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||Boulder; cobble; pebble|
|Zone||Circalittoral - lower, Circalittoral - upper|
|Depth Band||5-10 m, 10-20 m, 20-30 m|
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.
This variant is typically found on very exposed to moderately exposed, circalittoral mixed substrata subject to moderately strong tidal streams. It most frequently occurs between 10m and 20m water depth. This variant is characterised by a dense hydroid and Flustra foliacea turf, along with other scour-tolerant species, growing on the more stable boulders and cobbles which overlie coarse muddy sand and gravel. Although Nemertesia antennina is the dominant species within the hydroid turf, other species such as Halecium halecinum, Nemertesia ramosa and Hydrallmania falcata may also be present. Other bryozoans found amongst the hydroid and Flustra turf include Cellepora pumicosa, Bugulina flabellata, Bugulina turbinata, and a crisiid turf. Encrusting red algae, the polychaete Spirobranchus triqueter and barnacles such as Balanus crenatus may be found on the smaller cobbles and pebbles, which may become mobile during extreme storms. Echinoderms such as Asterias rubens and Ophiothrix fragilis may be present on the boulders, or the coarse sediment in between. On the larger, more stable boulders, isolated sponge communities may develop, with species such as Sycon ciliatum, Dysidea fragilis, Hemimycale columella, Amphilectus fucorum and Stelligera montagui. In addition, small Alcyonium digitatum, various ascidians (Clavelina lepadiformis, Botryllus schlosseri), Pododesmus patelliformis and top shells (Calliostoma zizyphinum, Steromphala cineraria) may colonise the upper faces and vertical sides of larger boulders. At some shallower sites, the foliose red algae Hypoglossum hypoglossoides may be found on the tops of larger boulders. Within the coarse sediment underlying these boulders and cobbles, anemones such as Cerianthus lloydii and Urticina felina may be recorded. Under-boulder fauna typically consists of terebellid worms, and crabs such as Pisidia longicornis and Cancer pagurus.
This variant is found in wave-exposed locations, resulting in kelp forest in the infralittoral zone being dominated by Alaria esculentus and Laminaria hyperborea. When the substratum becomes rockier, this biotope will graduate into the variant FluCoAs.SmAs.
|Taxon||Relative importance of taxon for defining this community (%)||Typical abundance - SACFOR scale||% of core records where taxon was recorded|
Similar biotopes or habitat types
CR.HCR.XFa.FluCoAs.PaurThis variant occurs on slightly less wave-exposed sites but subject to similar tidal streams. While CR.HCR.XFa.FluCoAs.Paur is found on circalittoral bedrock and boulders, CR.HCR.XFa.FluCoAs.X occurs on mixed substrata (boulders, cobble, pebble and gravel). Although both biotopes feature F. foliacea as a dominant feature of their fauna, CR.HCR.XFa.FluCoAs.X has a much more diverse associated fauna and lacks the abundant sheets of the colonial ascidian Polyclinum aurantium characteristic of CR.HCR.XFa.FluCoAs.Paur.
CR.HCR.XFa.FluCoAs.SmAsThis variant occurs under slightly less wave-exposed conditions but subject to similar tidal streams. They both occur around similar depths but CR.HCR.XFa.FluCoAs.X is found on a mixed substratum (boulders, cobbles, pebbles and gravel) whereas CR.HCR.XFa.FluCoAs.SmAs tends to be found on bedrock or boulders. CR.HCR.XFa.FluCoAs.SmAs usually has a more diverse range of sponges, although it tends not to have the range of species found on more mixed sediment as in CR.HCR.XFa.FluCoAs.X (e.g. Cerianthus lloydii, Chaetopterus variopedatus and Mimachlamys varia).