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Marine Habitat Classification

Description of biotope or habitat type

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   Modiolus modiolus beds with Chlamys varia, sponges, hydroids and bryozoans on slightly tide-swept very sheltered circalittoral mixed substrata

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Sheltered, Very sheltered
Tidal streams Strong (3-6 kn), Moderately strong (1-3 kn), Weak (>1 kn)
Substratum Pebble, gravel and shells on sandy mud sediments
Zone Circalittoral, Infralittoral
Depth Band 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 SS.SBR.SMus.ModCvar <I>Modiolus modiolus</I> beds with <I>Chlamys varia</I>, sponges, hydroids and bryozoans on slightly tide-swept very sheltered 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.


Dense Modiolus modiolus beds, covered by hydroids and bryozoans, on soft gravelly, shelly mud with pebbles in areas of slight or moderate tidal currents. The variable scallop (Chlamys varia) is frequently found in large numbers amongst the Modiolus shells. Hydroids such as Halecium spp. and Kirchenpaueria pinnata and ascidians such as Ascidiella aspersa, Corella parallelogramma and Ciona intestinalis may be found attached to pebbles or mussel shells. The echinoderms Ophiothrix fragilis and Antedon bifida are often frequent in this biotope as is the encrusting polychaete Pomatoceros triqueter. Similar communities have been found on cobble and pebble plains in stable, undisturbed conditions in some sealochs, although not all these examples have Modiolus beds.


No situtation data available.

Temporal variation

No temporal data available.

Characterising species

Taxon Typical abundance - SACFOR scale % of core records where taxon was recorded
Halecium halecinum Frequent 21-40 %
Kirchenpaueria pinnata Frequent 41-60 %
Alcyonium digitatum Occasional 61-80 %
Cerianthus lloydii Occasional 41-60 %
Urticina felina Occasional 41-60 %
Terebellidae Occasional 41-60 %
Pomatoceros triqueter Frequent 81-100 %
Serpula vermicularis Occasional 21-40 %
Protula tubularia Frequent 41-60 %
Balanus balanus Occasional 41-60 %
Pagurus bernhardus Occasional 41-60 %
Hyas araneus Occasional 61-80 %
Inachus dorsettensis Occasional 41-60 %
Macropodia rostrata Occasional 61-80 %
Liocarcinus depurator Occasional 61-80 %
Gibbula cineraria Occasional 41-60 %
Calliostoma zizyphinum Occasional 41-60 %
Buccinum undatum Occasional 81-100 %
Pleurobranchus membranaceus Frequent 61-80 %
Modiolus modiolus Common 81-100 %
Aequipecten opercularis Occasional 41-60 %
Chlamys varia Occasional 81-100 %
Antedon bifida Frequent 61-80 %
Crossaster papposus Rare 41-60 %
Asterias rubens Frequent 81-100 %
Ophiothrix fragilis Frequent 81-100 %
Ophiocomina nigra Occasional 61-80 %
Ophiura albida Occasional 41-60 %
Psammechinus miliaris Frequent 41-60 %
Echinus esculentus Occasional 81-100 %
Thyone fusus Rare 21-40 %
Thyone roscovita Occasional 41-60 %
Thyonidium drummondii Occasional 21-40 %
Ciona intestinalis Occasional 41-60 %
Corella parallelogramma Occasional 41-60 %
Ascidiella aspersa Frequent 41-60 %
Pyura microcosmus Occasional 21-40 %
Corallinaceae Frequent 41-60 %
Lithothamnion glaciale Occasional 61-80 %
Phycodrys rubens Frequent 41-60 %
Laminaria hyperborea Common 41-60 %

Similar biotopes or habitat types

ModHAs is less species rich with far fewer sponges and hydroids growing on and amongst the Modiolus and few if any Chlamys varia

Classification history of this biotope or habitat type

Classification version Code
96.7 SCR.ModSHBy

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