Community composition will depend upon a combination of factors, including the stability of the bed, the substratum type, salinity, tidal exposure and location. Of the three species of Zostera, diversity tends to be lowest in the intertidal, estuarine, annual beds of Z. noltii (Jacobs & Huisman, 1982). Wildfowl (ducks and geese) are among the few animals which graze directly upon Zostera and are able to digest its leaves. Eelgrasses provide shelter and hiding places. The leaves and rhizomes provide substrata for the settlement of epibenthic species which in turn may be grazed upon by other species.

Eelgrass beds are widely recognised to be important spawning and nursery areas for many species of fish, including commercial species.

Dense meadows of eelgrass leaves increase rates of sedimentation, and the rhizome and root networks bind the sediment, thereby reducing erosion. The roots also allow oxygen to penetrate into otherwise impermeable sediments. The penetration of Zostera roots into the sediment aerates the upper layers and provides a more favourable habitat for burrowing animals.

Eelgrass primary production supports a rich, resident fauna and as a result, the beds are used as a refuge and nursery area by many species. The decomposition of dead eelgrass tissue by bacteria drives detritus-based food chains within the Zostera bed. High numbers of heterotrophic protists are found in the water column over eelgrass meadows and take up both the dissolved organics leaching from the eelgrasses and the rapidly multiplying bacteria.

Since the occurrence of the wasting disease which led to the widespread loss of Zostera marina beds throughout Europe and North America in the 1920s-30s, the relative importance of the different Zostera species in Brent geese diet has shifted. As a result of the decline of Z. marina and its slow recovery, Brent geese were forced to migrate to other feeding areas and to switch their feeding to intertidal beds of Z. angustofolia and Z. noltii. Zostera noltii has replaced Z. marina as the preferred food and currently provides the main source of energy for Brent geese overwintering in Britain. Burton (1961) studied the dark-bellied Brent geese on the Essex coast in the late 1950s and early 1960s and found that they fed almost entirely on Z. noltii and the alga Enteromorpha sp. This shift in eelgrass abundance from Z. marina to Z. noltii has also affected wigeon. Wigeon numbers have declined dramatically in recent years and the reduced availability of eelgrass is considered to be one of the contributory factors. Grazing wigeon are very vulnerable to human disturbance. Where wildfowling is popular, wigeon appear to avoid the Z. noltii beds near the top of the shore and only begin to feed there when the Z. angustifolia and Z. marina lower down the shore are exhausted (Percival & Evans 1997).

New leaves appear in spring and the eelgrass meadows develop over the intertidal flats in the summer. Leaf growth ceases around September or October (Brown 1990), and leaf cover begins to decline during the autumn and over the winter. Plants may experience a complete loss of foliage, dying back to the buried rhizomes.

In perennial populations, the rhizomes survive the winter to produce new leaves the following spring, while in annual populations, both the leaves and rhizomes die.

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