COMPOSITION, DISTRIBUTION AND BIOMASS OF MEIOBENTHOS IN THE OOSTERSCHELDE ESTUARY (SW NETHERLANDS)

Meiofauna composition, abundance, biomass, distribution and diversity were investigated for 31 stations in summer. The sampling covered the whole Oosterschelde and comparisons between the subtidal - intertidal and between the western-central - eastern compartment were made. Meiof auna had a community density ranging between 200 and 17 500 ind 10 CM- 2, corresponding to a dry weight of 0.2 and 8.4 gm-2 . Abundance range d between 130 and 17 200 ind 10 CM-2 for nematodes and between 10 and 1600 ind 10 cm-2 for copepods. Dry weight biomass of these taxa was be tween 0.5-7.0 gm-2 and 0.008-0.3 gm-2 for nematodes and copepods respe ctively. The meiofauna was strongly dominated by the nematodes (36-99% ), who's abundance, biomass and diversity were significantly higher in tertidally than subtidally and significantly higher in the eastern par t than in the western part. High numbers were positively correlated wi th the percentage silt and negatively with the median grain size of th e sand fraction. The abundance and diversity of the copepods were high est in the subtidal, but their biomass showed an inverse trend being h ighest on the tidal flats. The taxa diversity of the meiofauna communi ty and species diversity of both the nematodes and the copepods were h igher in subtidal stations than on tidal flats. In the subtidal, the m eiofauna and copepod diversity decreased from west to east, whereas ne matode diversity increased. The vertical profile clearly reflected the sediment characteristics and could be explained by local hydrodynamic conditions. Seasonal variation was pronounced for the different taxa with peak abundance in spring, summer or autumn and minimum abundance in winter. Changes in tidal amplitude and current velocity enhanced by the storm-surge barrier will alter the meiofauna community structure. As a result meiofauna will become more important in terms of density and biomass, mainly due to increasing numbers of nematodes, increasing bioturbation, nutrient mineralisation and sustaining bacterial growth . A general decrease in meiofauna diversity is predicted. The number o f copepods is expected to decrease and interstitial species will be re placed by epibenthic species, the latter being more important in terms of biomass and as food for the epibenthic macrofauna and fishes.