Description of biotope or habitat type

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   Mytilus edulis beds on littoral sand

Description

This sub-biotope occurs on mid to lower shore sand and muddy sand. Mussels Mytilus edulis grow attached to shell debris and live cockles Cerastoderma edule, forming patches of mussels on consolidated shell material, and often growing into extensive beds. The mussel valves are usually encrusted with barnacles such as Austrominius modestus and Semibalanus balanoides, and the mussel bed provides a habitat for a range of species including Littorina littorea. The sediment infaunal community is usually rich and very similar to that of cockle beds (CerPo), including cockles Cerastoderma edule, the baltic tellin Macoma balthica, and a range of burrowing crustaceans and polychaetes typical for CerPo. Further species may be present are the sand mason Lanice conchilega, the sand gaper Mya arenaria, the peppery furrow shell Scrobicularia plana, Nephtys spp., and the ragworm Hediste diversicolor. Scattered fronds of eelgrass Zostera noltei may occur.

Situation

This biotope often occurs in large sandy estuaries, or on enclosed shores, alongside other sand and muddy sand biotopes, most notably CerPo. It is possible that Lanice beds (Lan) occur lower down on the shore.

Temporal variation

Where this sub-biotope occurs in very sheltered conditions on muddy sand, it could change to Myt.Mu over time as pseudofaeces build up forming a layer of mud. This cannot happen where wave action or tidal streams wash away pseudofaeces and prevent a build up. In areas where mussel spat ("mussel crumble") settles on the surface shell layer of cockle beds, the mussel cover may be ephemeral, as is the case in the Burry Inlet.

Characterising species

Characterising species data not applicable.

Similar biotopes or habitat types

LS.LSa.MuSa.CerPo

Occurs in very similar physical conditions. M. edulis is not present or only present in low abundances, and does not form beds on the sediment surface. The infaunal community is very similar.

LS.LBR.LMus.Myt.Mx

Occurs on mixed substrata, often in more exposed conditions near predominantly rocky areas. Cobbles and boulders support epifaunal species typical of rocky shores, whereas the sediment infauna is more limited.

LS.LBR.LMus.Myt.Mu

Occurs in more sheltered conditions on mudflats. The sediment is anoxic and the infauna therefore a lot less diverse than that of LS.LBR.LMus.Myt.Sa. Cockles C. edule do not occur.

Classification history of this biotope or habitat type