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Marine Habitat Classification


Description of biotope or habitat type

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   Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders


Habitat (physical) 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.

Distribution of habitat CR.HCR.XFa.FluCoAs.SmAs <I>Flustra foliacea</I>, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders

  • 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 10-20m 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, Bugula flabellata, Bugula 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, Sagartia 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 Scypha ciliata, Cliona celata, Esperiopsis 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
Scypha ciliata 3 Frequent 61-80 %
Cliona celata 1 Occasional 61-80 %
Esperiopsis fucorum 1 Frequent 41-60 %
Dysidea fragilis 1 Occasional 41-60 %
Tubularia indivisa 1 Occasional 41-60 %
Abietinaria abietina 1 Occasional 41-60 %
Hydrallmania falcata 2 Frequent 61-80 %
Sertularia argentea 2 Frequent 61-80 %
Nemertesia antennina 2 Frequent 61-80 %
Alcyonium digitatum 3 Occasional 61-80 %
Urticina felina 4 Frequent 81-100 %
Sagartia elegans 2 Occasional 61-80 %
Sabellaria spinulosa 2 Frequent 41-60 %
Balanus crenatus 4 Common 61-80 %
Cancer pagurus 2 Occasional 61-80 %
Necora puber 2 Occasional 61-80 %
Calliostoma zizyphinum 1 Occasional 41-60 %
Alcyonidium diaphanum 6 Frequent 81-100 %
Flustra foliacea 6 Frequent 81-100 %
Bugula flabellata 3 Occasional 61-80 %
Bugula plumosa 2 Frequent 61-80 %
Bicellariella ciliata 1 Occasional 41-60 %
Crossaster papposus 2 Occasional 61-80 %
Henricia 3 Occasional 41-60 %
Asterias rubens 6 Frequent 81-100 %
Clavelina lepadiformis 1 Occasional 41-60 %
Polyclinum aurantium 1 Frequent 41-60 %
Polycarpa scuba 2 Frequent 41-60 %
Dendrodoa grossularia 2 Frequent 41-60 %
Botryllus schlosseri 1 Occasional 41-60 %
Molgula manhattensis 2 Frequent 41-60 %

Similar biotopes

CR.HCR.XFa.FluCoAs.Paur
This variant occurs on moderately wave-exposed sites but subject to similar tidal streams as FluCoAs.SmAs. Although both sub-biotopes are dominated by F. foliacea, FluCoAs.SmAs has a much more diverse associated sponge fauna and lacks the abundant sheets of the colonial ascidian Polyclinum aurantium characteristic of 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 FluCoAs.SmAs is found on bedrock and boulders. 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 Chlamys varia).

CR.HCR.XFa.ByErSp.DysAct
This sub-biotope occurs under more wave-exposed conditions, with slightly stronger tides than 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 ByErSp.DysAct, it is not present in the same abundance as in FluCoAs.SmAs, where it forms dense aggregations on the bedrock and boulders. In addition, species such as Caryophyllia smithii and Corynactis viridis are absent from FluCoAs.SmAs.

CR.MCR.EcCr.FaAlCr.Flu
This sub-biotope occurs over a similar range of wave-exposures but tends to occur in sites subject to moderately strong to weak tidal streams. This biotope is found deeper than FluCoAs.SmAs, with a mean depth range of 20m to 21m. Both sub-biotopes tend to occupy the same type of substrata (bedrock, boulder, cobble and sand influenced). This sub-biotope has a much more impoverished fauna (especially sponge fauna) when compared to FluCoAs.SmAs. Key species which are absent in FaAlCr.Flu but present in FluCoAs.SmAs include S. argentea, B. crenatus, B. plumosa and S. ciliata.

Photos

CR.HCR.XFA.FluCoAs.SmAs Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders, E of Start Point, North Sanday. ANON © JNCC
CR.HCR.XFA.FluCoAs.SmAs Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders, E of Start Point, North Sanday. ANON © JNCC
CR.HCR.XFA.FluCoAs.SmAs Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders, N of Filey Brigg. Eleanor Murray © JNCC
CR.HCR.XFA.FluCoAs.SmAs Flustra foliacea, small solitary and colonial ascidians on tide-swept circalittoral bedrock or boulders, N of Filey Brigg. Eleanor Murray © JNCC

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