Description of biotope or habitat type

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   Amphipods and Scolelepis spp. in littoral medium-fine sand

Description

Mobile clean sandy beaches on exposed and moderately exposed shores, with sediment grain sizes ranging from medium to fine, often with a fraction of coarser sediment. The sediment contains little or no organic matter, and usually no anoxic layer is present at all. It tends to be well-drained, retaining little water at low tide, though the sediment of the AmSco.Pon sub-biotope may remain damp throughout the tidal cycle. These beaches usually occur under fully marine conditions, though the AmSco.Eur sub-biotope may occur under moderately exposed lower estuarine conditions. The mobility of the sediment leads to a species-poor community, dominated by polychaetes, isopods and burrowing amphipods. Scolelepis spp. can tolerate well-drained conditions, and are often present in well-draining, coarser sand. Burrowing amphipods that often occur in this biotope include Bathyporeia spp., Pontocrates arenarius, and Haustorius arenarius. The isopod Eurydice pulchra is also often present. On semi-exposed beaches with a moderate tide range where there is a marked high-shore berm, there can be a marked seepage at the foot of the berm that probably carries the products of the organic matter derived from strand line breakdown. Here in a narrow zone, exceptionally high populations of Bathyporeia pilosa, sometimes above 10000 per square metre, may occur. The zone may be narrower than the strandline and could easily be missed on surveys were only a few levels are sampled. Three sub-biotopes are described for this biotope, based principally on differences in infaunal species composition.

Situation

Situated mainly on the mid and lower shore, sometimes upper shore, of exposed to moderately exposed beaches. Under more exposed conditions, it may occur below BarSa, or BarSh. Under more sheltered conditions, it may occur above the Po communities. Tal may be present on the same shores as AmSco, where driftlines of decomposing seaweed and other debris occur on the upper shore.

Temporal variation

Winter storms may reduce the number of or temporarily remove macroinvertebrates from exposed sandy beaches, with the sediment becoming re-colonised during the summer months.

Characterising species

Similar biotopes or habitat types

LS.LSa.MoSa.BarSa

Occurs in more mobile, coarser sand, often higher on the shore. The mobility and degree of drainage of the sediments enables very few, if any, individuals of hardy species to survive.

LS.LSa.FiSa.Po

Occurs in more stable, finer sediments, sometimes lower on the shore. The increased sediment stability enables a more diverse infaunal community to survive, including a range of polychaetes such as Arenicola marina and Nephtys spp., and the bivalve Macomangulus tenuis.

Classification history of this biotope or habitat type