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Marine Habitat Classification

Description of biotope or habitat type

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   Flustra foliacea and Hydrallmania falcata on tide-swept circalittoral mixed sediment

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 Boulders, cobbles or pebbles with gravel and sand
Zone Circalittoral
Depth Band 5-10 m, 10-20 m, 20-30 m, 30-50 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 SS.SMx.CMx.FluHyd <I>Flustra foliacea</I> and <I>Hydrallmania falcata</I> on tide-swept circalittoral mixed sediment

  • 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 represents part of a transition between sand-scoured circalittoral rock where the epifauna is conspicuous enough to be considered as a biotope and a sediment biotope where an infaunal sample is required to characterise it and is possibly best considered an epibiotic overlay. Flustra foliacea and the hydroid Hydrallmania falcata characterise this biotope; lesser amounts of other hydroids such as Sertularia argentea, Nemertesia antennina and occasionally Nemertesia ramose, occur where suitably stable hard substrata is found. The anemone Urticina feline and the soft coral Alcyonium digitatum may also characterise this biotope. Barnacles Balanus crenatus and tube worms Pomatoceros triqueter may be present and the robust bryozoans Alcyonidium diaphanum and Vesicularia spinosa appear amongst the hydroids at a few sites. Sabella pavonina and Lanice conchilega may be occasionally found in the coarse sediment around the stones. In shallower (i.e. upper circalittoral) examples of this biotope scour-tolerant robust red algae such as Polysiphonia nigrescens, Calliblepharis spp. and Gracilaria gracilis are found.


This biotope is found around most coasts, although regional differences are seen where one or two similarly scour-tolerant species such as Styela clava and Crepidula fornicata (Solent) occupy the hard substrata

Temporal variation

No temporal data available.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Halecium halecinum 1 Occasional 21-40 %
Hydrallmania falcata 11 Occasional 61-80 %
Sertularia argentea 3 Occasional 41-60 %
Nemertesia antennina 7 Occasional 41-60 %
Nemertesia ramosa 1 Occasional 21-40 %
Alcyonium digitatum 5 Occasional 41-60 %
Urticina felina 8 Occasional 61-80 %
Pomatoceros triqueter 3 Occasional 41-60 %
Balanus crenatus 1 Frequent 21-40 %
Pagurus bernhardus 6 Occasional 41-60 %
Alcyonidium diaphanum 5 Occasional 41-60 %
Vesicularia spinosa 2 Frequent 21-40 %
Flustra foliacea 18 Frequent 81-100 %
Crossaster papposus 2 Occasional 21-40 %
Asterias rubens 10 Occasional 61-80 %

Similar biotopes or habitat types

With increased scouring and more sand S. cupressina becomes more common and FluHyd may develop into ScupHyd.

On pebble plains, as tidal stream strength increases to a point at which the stones are regularly mobilised, all hydroids are scoured off leaving just Pomatoceros, bryozoan crusts, Balanus crenatus and coralline algae.

CreAsAn is found in shallower water in slightly less exposed areas with a lower proportion of cobbles and pebbles and in slightly weaker currents.

Classification history of this biotope or habitat type

Classification version Code
97.06 MCR.Flu.SerHyd

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