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Marine Habitat Classification

Description of biotope or habitat type

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   Flustra foliacea and Haliclona oculata with a rich faunal turf on tide-swept circalittoral mixed substrata

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Exposed
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn)
Substratum Cobble; pebble; mud
Zone Circalittoral - lower
Depth Band 0-5 m, 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.

Distribution of habitat CR.HCR.XFa.FluHocu <I>Flustra foliacea</I> and <I>Haliclona oculata</I> with a rich faunal turf on tide-swept circalittoral mixed substrata

  • 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 biotope is typically found on exposed slopes of silty cobble and pebble subject to strong to moderate tidal streams. From afar, large 'finger' growths of the sponge Haliclona oculata occur amongst a rich faunal turf of hydroids and bryozoans with Flustra foliacea prominent. The dense faunal turf growing on the cobbles is composed of the bryozoans F. foliacea, Alcyonidium diaphanum and Crisia eburnea and sporadic occurrences of the hydroids Nemertesia antennina, Hydrallmania falcata, Ectopleura larynx, Rhizocaulus verticillatus and Halecium halecinum. Caprellid shrimps may be observed within this faunal turf. The hard substratum frequently has a dense covering of the sponge H. oculata and occasionally Amphilectus fucorum, while the softer gravely/sand between the cobbles provides a habitat for anemones such as Urticina felina and Cerianthus lloydii. The nudibranch Antiopella cristata may be seen preying on the faunal turf and the fan worm Sabella pavonia is occasionally seen amongst the cobbles. The soft coral Alcyonium digitatum is often attached to the upper faces of more stable cobbles and rocks, while in the crevices between cobbles, the anemone Cylista elegans, the crab Cancer pagurus, the prawn Pandalus montagui and the amphipod Dyopedos porrectus may be observed. Under-cobble fauna includes terebellid worms and Harmothoe spp. This biotope has been recorded from the Menai Strait, Milford Haven and Morecambe Bay.


No situation data available.

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
Dyopedos porrectus 7 Frequent 81-100%
Nemertesia antennina 6 Frequent 81-100%
Urticina felina 6 Frequent 81-100%
Alcyonidium diaphanum 5 Frequent 81-100%
Alcyonium digitatum 5 Frequent 81-100%
Cancer pagurus 5 Frequent 81-100%
Flustra foliacea 5 Frequent 81-100%
Haliclona oculata 5 Frequent 81-100%
Asterias rubens 4 Frequent 81-100%
Cylista elegans 4 Occasional 81-100%
Seraphsidae 4 Occasional 81-100%
Cerianthus lloydii 3 Occasional 81-100%
Hydrallmania falcata 3 Occasional 81-100%
Sabella pavonina 3 Frequent 81-100%
Pycnogonida 2 81-100%
Balanus crenatus 2 Frequent 61-80%
Caprellidae 2 81-100%
Halecium halecinum 2 Occasional 81-100%
Pandalus montagui 2 Occasional 61-80%
Rhizocaulus verticillatus 2 Occasional 61-80%
Ectopleura larynx 2 Occasional 81-100%
Crisia eburnea 1 Rare 81-100%
Amphilectus fucorum 1 Occasional 61-80%
Harmothoe 1 81-100%
Antiopella cristata 1 Rare 81-100%

Similar biotopes or habitat types

This biotope occurs on shallow circalittoral bedrock and cobbles, subject to moderate exposure and moderately strong tidal streams. F. foliacea is also prevalent in this community, but has a more diverse ascidian and bryozoan community than CR.HCR.XFa.FluHocu, including Molgula manhattensis and Alcyonidium diaphanum respectively.

This biotope occurs on moderately exposed circalittoral bedrock and boulders, subject to moderately strong tidal streams. This biotope is subject to considerable sand scour, and has an impoverished fauna dominated by Flustra foliacea and Alcyonium digitatum. CR.HCR.XFa.FluHocu has a higher diversity of species than CR.MCR.EcCr.FaAlCr.

This biotope occurs on moderately exposed bedrock, unlike CR.HCR.XFa.FluHocu which tends to occur on a cobblier substratum. This biotope does experience similar tidal stream regimes as CR.HCR.XFa.FluHocu. While F. foliacea is the dominant bryozoan, it is the presence of dense aggregations of Polyclinium aurantium which distinguish CR.HCR.XFa.FluCoAs.Paur as a separate biotope.

See other variants in the CR.HCR.XFa.FluCoAs biotope.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) CR.MCR.ByH.Flu.Hocu

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