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Marine Habitat Classification

Description of biotope or habitat type

To understand more about what this page is describing, see How to use the classification. See also How to cite.

   Circalittoral mixed sediment

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Moderately exposed, Sheltered, Very sheltered
Tidal streams Moderately strong (1-3 kn), Weak (>1 kn), Very weak (negligible)
Substratum Mixed sediment (with stones and shells)
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/infauna

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 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.


Mixed (heterogeneous) sediment habitats in the circalittoral zone (generally below 15-20 m) including well mixed muddy gravelly sands or very poorly sorted mosaics of shell, cobbles and pebbles embedded in or lying upon mud, sand or gravel. Due to the variable nature of the seabed a variety of communities can develop which are often very diverse. A wide range of infaunal polychaetes, bivalves, echinoderms and burrowing anemones such as Cerianthus lloydii are often present in such habitats and the presence of hard substrata (shells and stones) on the surface enables epifaunal species to become established, particularly hydroids such as Nemertesia spp. and Hydrallmania falcata. The combination of epifauna and infauna can lead to species rich communities. Coarser mixed sediment communities may show a strong resemblance, in terms of infauna, to biotopes within the SS.SCS complex. However, infaunal data for this biotope complex is limited to that described under the biotope SS.SMx.CMx.KurThyMx, and so are not representative of the infaunal component of this biotope complex.


No situation data available.

Temporal variation

No temporal data available.

Characterising species

Taxon Typical abundance - SACFOR scale % of core records where taxon was recorded
Prionospio fallax Abundant 61-80%
Asterias rubens Occasional 61-80%
Thyasira flexuosa Common 81-100%
Cerianthus lloydii Frequent 41-60%
Kurtiella bidentata Frequent 81-100%
Pagurus bernhardus Occasional 41-60%
Chaetozone setosa Common 81-100%
Corallinaceae Occasional 21-40%
Hilbigneris gracilis Common 81-100%
Alcyonium digitatum Occasional 21-40%
Nematoda Frequent 61-80%
Buccinum undatum Occasional 21-40%
Scoloplos armiger Abundant 81-100%
Crossaster papposus Rare 21-40%
Abra alba Common 41-60%
Lanice conchilega Occasional 21-40%
Ampelisca tenuicornis Frequent 61-80%
Liocarcinus depurator Occasional 21-40%
Chamelea gallina Common 61-80%
Nemertesia antennina Occasional 21-40%
Goniada maculata Common 61-80%
Nemertesia ramosa Occasional 21-40%
Mediomastus fragilis Common 41-60%
Ophiocomina nigra Frequent 21-40%
Nemertea Common 61-80%
Ophiothrix fragilis Common 21-40%
Nephtys hombergii Common 61-80%
Ophiura albida Frequent 21-40%
Owenia fusiformis Common 61-80%
Pecten maximus Occasional 21-40%
Pholoe inornata Frequent 61-80%
Spirobranchus triqueter Occasional 21-40%
Phoronis Common 41-60%
Psolus phantapus Occasional 21-40%
Scalibregma inflatum Common 61-80%
Seraphsidae Occasional 21-40%
Spiophanes bombyx Frequent 61-80%
Thyone fusus Occasional 21-40%
Terebellides stroemii Abundant 61-80%
Urticina felina Occasional 21-40%
Amphiura filiformis Abundant 41-60%
Modiolus modiolus Occasional 21-40%
Eudorella truncatula Abundant 41-60%
Echinus esculentus Occasional 21-40%
Galathowenia oculata Frequent 41-60%
Flustra foliacea Occasional 1-20%
Glycera alba Abundant 41-60%
Hydrallmania falcata Occasional 1-20%
Levinsenia gracilis Common 41-60%
Nephtys Common 41-60%
Phaxas pellucidus Common 41-60%

Similar biotopes or habitat types

Not applicable or unknown.

Classification history of this biotope or habitat type

Classification version Code Habitat name
2015 (15.03) SS.SMx.CMx Circalittoral mixed sediment
2004 (04.05) SS.SMx.CMx Circalittoral mixed sediment
1997 (97.06) SS.CMX Circalittoral mixed sediments

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