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 |
Biotope origin
| Derived using data from | Various |
| Faunal group | Epifauna |
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 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 ramosa, occur where suitably stable hard substrata is found. The anemone Urticina felina and the soft coral Alcyonium digitatum may also characterise this biotope. Barnacles Balanus crenatus and tube worms Spirobranchus 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. In offshore areas, such as in the Greater Gabbard North Sea Area, where there is circalottoral mixed sediment, with pebbles and gravels, the biotope may further support rich encrusting fauna, including bryozoans, Spirobranchus lamarcki, and the barnacle Verruca stroemia, and occasionally Sabellaria spinulosa. Alongside these encrusting fauna, infauna such as Lumbrinerids (Hilbigneris gracilis), Glycera lapidum, Echinocyamus pusillus, Amphipholis squamata, Caulleriella alata may be present, and may represent a transitionary form between SS.SMx.CMx.FluHyd and SS.SCS.CCS.MedLumVen.
Situation
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. Further offshore in the North Sea Flustra foliacea is less dominant and a hydroid turf and encrusting species more prevalent.
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 |
|---|---|---|---|
| Flustra foliacea | 18 | Frequent | 81-100% |
| Hydrallmania falcata | 11 | Occasional | 61-80% |
| Asterias rubens | 10 | Occasional | 61-80% |
| Urticina felina | 8 | Occasional | 61-80% |
| Nemertesia antennina | 7 | Occasional | 41-60% |
| Pagurus bernhardus | 6 | Occasional | 41-60% |
| Alcyonidium diaphanum | 5 | Occasional | 41-60% |
| Alcyonium digitatum | 5 | Occasional | 41-60% |
| Spirobranchus triqueter | 3 | Occasional | 41-60% |
| Sertularia argentea | 3 | Occasional | 41-60% |
| Crossaster papposus | 2 | Occasional | 21-40% |
| Vesicularia spinosa | 2 | Frequent | 21-40% |
| Balanus crenatus | 1 | Frequent | 21-40% |
| Halecium halecinum | 1 | Occasional | 21-40% |
| Nemertesia ramosa | 1 | Occasional | 21-40% |
Similar biotopes or habitat types
SS.SSa.IFiSa.ScupHyd
With increased scouring and more sand S. cupressina becomes more common and SS.SMx.CMx.FluHyd may develop into SS.SSa.IFiSa.ScupHyd.
SS.SCS.CCS.SpiB
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 Spirobranchus, bryozoan crusts, Balanus crenatus and coralline algae.
SS.SMx.IMx.CreAsAn
SS.SMx.IMx.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 | Habitat name |
|---|---|---|
| 2015 (15.03) | SS.SMx.CMx.FluHyd | Flustra foliacea and Hydrallmania falcata on tide-swept circalittoral mixed sediment |
| 2004 (04.05) | SS.SMx.CMx.FluHyd | Flustra foliacea and Hydrallmania falcata on tide-swept circalittoral mixed sediment |
| 1997 (97.06) | SS.MCR.ByH.Flu.SerHyd and part of SS.MCR.ByH.SNemAdia | Flustra foliacea and other hydroid/bryozoan turf species on slightly scoured circalittoral rock or mixed substrata and part of Sparse sponges, Nemertesia spp., Alcyonidium diaphanum and Bowerbankia spp. on circalittoral mixed substrata |