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Marine Habitat Classification

Description of biotope or habitat type

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   Mytilus edulis and piddocks on eulittoral firm clay

Physical habitat description

Salinity Full (30-35 ppt)
Wave exposure Exposed, Moderately exposed
Tidal streams
Substratum Clay; cobbles
Zone Eulittoral
Depth Band Lower shore
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 LR.MLR.MusF.MytPid <I>Mytilus edulis</I> and piddocks on eulittoral firm clay

  • 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'

Point data based on records in the UK Marine Recorder Snapshot.


Clay outcrops in the mid to lower eulittoral which are bored by a variety of piddocks including Pholas dactylus, Barnea candida and Petricolaria pholadiformis. The surface of the clay is characterised by small clumps of the mussel Mytilus edulis, the barnacle Austrominius modestus and the winkle Littorina littorea. Seaweeds are generally sparse on the clay, although small patches of the red seaweeds Mastocarpus stellatus, Halurus flosculosus and Ceramium spp. can occur, usually attached to loose-lying cobble or mussel shells. Also the green seaweeds Ulva spp. and Ulva lactuca may be present. The sand mason Lanice conchilega can sometimes be present in the clay, while the shore crab Carcinus maenas is present as well. More data are required to validate this description.


MytPid can usually be found beneath a M. edulis or barnacle and Littorina spp.-dominated biotope (Myt.Myt; BLitX). It is found above a Laminaria digitata and piddocks-dominated biotope (Ldig.Pid).

Temporal variation

The C. maenas population may migrate offshore during the winter season.

Characterising species

Taxon Relative importance of taxon for defining this community (%) Typical abundance - SACFOR scale % of core records where taxon was recorded
Mytilus edulis 24 Frequent 81-100%
Carcinus maenas 16 Frequent 81-100%
Barnea candida 11 Frequent 41-60%
Ulva intestinaloides 8 Abundant 41-60%
Ulva lactuca 6 Frequent 41-60%
Austrominius modestus 5 Occasional 41-60%
Littorina littorea 5 Frequent 41-60%
Halurus flosculosus 4 Common 21-40%
Petricolaria pholadiformis 4 Frequent 21-40%
Mastocarpus stellatus 2 Occasional 21-40%
Ceramium 1 Frequent 21-40%
Lanice conchilega 1 Rare 21-40%
Pholas dactylus 1 Frequent 21-40%

Similar biotopes or habitat types

Occurs on fossilised peat and chalk. It has a higher density of ephemeral seaweeds such as Ulva intestinalis and Ceramium spp. while M. edulis and E. modestus are usually absent.

Classification history of this biotope or habitat type

Classification version Code
1997 (97.06) MLR.MytPid
1996 (6.95) MLR.Myt.Pid

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