Hediste diversicolor, Macoma balthica and Mya arenaria in sandy mud shores
|Within Vocab||Marine Habitat Classification for Britain and Ireland Version 97.06|
|Definition||Mid and low shore sandy mud in fully marine and variable salinity, sheltered to extremely sheltered estuaries, bays and marine inlets. This sub-type biotope of LMU.HedMac is differentiated from other LMU.HedMac biotopes in having Mya arenaria in high densities in most cases. Polychaetes Eteone longa, Hediste (Nereis) diversicolor, Pygospio elegans, oligochaetes, the mud-burrowing amphipod Corophium volutator, the mud snail Hydrobia ulvae, the cockle Cerastoderma edule, the Baltic tellin Macoma balthica and the soft clam Mya arenaria are the most frequently recorded and characterising species. The sediment is typically anoxic below 1 cm. The presence of Mya is usually indicated by jets of water of up to 50 cm high over the sediment surface, but should be confirmed through digging up the bivalve. The species that are found in LMU.HedStr can sometimes be present in high abundance in this biotope, reflecting the similarity of LMU.HedStr to this biotope. The tolerance to reduced salinity and substratum type of Mya arenaria is such that this biotope overlaps with LMS.MacAre and with LMU.HedStr; the significance of Mya arenaria as a characterising species is therefore unclear, but the conspicuousness of this species makes it a useful indicator of this habitat type. LMU.HedMac.Pyg is similar to this biotope, but contains very few Mya arenaria. LMU.HedScr can have a similarly rich bivalve component, but is usually restricted to reduced salinity mud habitats. LMU.HedOl has a much reduced polychaete and bivalve fauna compared to LMU.HedMac.Mare. This biotope is more muddy and probably more influenced by variable salinity than LMS.MacAre.Mare. A similar biotope that has a substratum with more gravel and pebbles and is limited to the lower shore is LMX.Mare. Like LMS.MacAre.Mare, the high densities of Mya arenaria can be very localised and be specific to certain estuaries or tributaries within estuaries over long periods of time.|
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