The surface of a sandy beach is liable to disturbance by wind and waves, and provides no firm anchorage for superficially attached plants and animals. There is consequently seldom much obvious surface-living flora and fauna. Where the sand contains embedded stones, certain algae can grow attached to these, for example, Chorda filum. In sheltered areas the deposit may be sufficiently stable to allow rooting plants such as eel-grass (Zostera) or cord grass (Spartina) to become established.
Usually the plant population consists only of a microscopic vegetation of diatoms and coloured flagellates existing in the interstices between the surface sand grains. Probably the majority are attached to the sand particles, brought to the surface or buried by movements of the sand by wind and waves. Others are motile and appear capable of rhythmical movements, forming green or brown patches on the shore surface at low tide and retreating below the surface as the tide advances. Mucilaginous secretions produced by microscopic algae are probably important in helping to stabilize fine sediments. Along the backshore, accumulations of wind-blown sand may form sand dunes, and when these are sufficiently stable they become consolidated by a characteristic dune vegetation, for example marram grass (Ammophila arenaria), sand couch grass (Agropyron junceiforme) and sand sedge (Carex arenaria).
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