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Marine Habitat Classification

Description of biotope or habitat type

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   Sparse Modiolus modiolus, dense Cerianthus lloydii and burrowing holothurians on sheltered circalittoral stones and mixed sediment

Physical habitat description

Salinity Full (30-35 ppt), Variable (18-35 ppt)
Wave exposure Sheltered, Very sheltered, Extremely sheltered
Tidal streams Weak (>1 kn), Very weak (negligible)
Substratum Pebbles, boulders and cobbles on mud or muddy gravel
Zone Infralittoral - lower, Circalittoral
Depth Band 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.ClloModHo Sparse <I>Modiolus modiolus</I>, dense <I>Cerianthus lloydii</I> and burrowing holothurians on sheltered circalittoral stones and 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.


Pebbles and cobbles on mud or muddy gravel in sealochs with frequent Cerianthus lloydii and occasional Modiolus modiolus. Large burrowing holothurians may include Psolus phantapus, Paracucumaria hyndmani, Thyonidium commune, Thyone fusus and Leptopentacta elongate. Many of these species only extend their tentacles above the sediment surface seasonally and are likely to be under recorded by epifaunal surveys. Other more conspicuous characterising taxa include Pagurus bernhardus, Asterias rubens, and Buccinum undatum. This biotope is well developed in the Clyde sealochs, although many examples are rather species-poor. Some examples in south-west Scottish sealochs have greater quantities of boulders and cobbles and therefore have a richer associated biota (compared with other sheltered Modiolus bed biotopes such as ModHAs). Examples in Shetland are somewhat different in having the cucumber Cucumaria frondosa amongst sparse Modiolus beds and a slightly different balance in abundance of other species; for example the brittlestar Ophiopholis aculeata is more abundant in these far northern examples in the voes and narrows


No situation data available.

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
Hydractinia echinata 2 Occasional 21-40 %
Alcyonium digitatum 2 Rare 41-60 %
Cerianthus lloydii 15 Frequent 81-100 %
Terebellidae 2 Occasional 41-60 %
Pomatoceros triqueter 4 Occasional 41-60 %
Pagurus bernhardus 16 Frequent 81-100 %
Munida rugosa 1 Occasional 21-40 %
Hyas araneus 1 Occasional 21-40 %
Liocarcinus depurator 3 Occasional 41-60 %
Carcinus maenas 2 Occasional 41-60 %
Buccinum undatum 5 Occasional 61-80 %
Modiolus modiolus 9 Occasional 61-80 %
Aequipecten opercularis 2 Occasional 41-60 %
Asterias rubens 8 Occasional 61-80 %
Ophiura albida 3 Frequent 41-60 %
Psammechinus miliaris 5 Occasional 41-60 %
Echinus esculentus 4 Occasional 41-60 %
Thyone fusus 1 Occasional 21-40 %
Corallinaceae 1 Occasional 21-40 %

Similar biotopes or habitat types

ModHAs occurs in similar physiographic features, although ClloModHo is in softer sediment in some cases, and with a much lower abundance of Modiolus, and a lower diversity in general. There may some overlap in these two biotopes as several of the holothurians extend their tentacles above the surface of the sediment for only a limited amount of time during the year.

Classification history of this biotope or habitat type

Classification version Code
97.06 CMX.ModHo
96.7 SCR.ModHo

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