EFFECT OF SEDIMENTOLOGICAL AND HYDRODYNAMICAL CHANGES IN THE INTERTIDAL AREAS OF THE OOSTERSCHELDE ESTUARY (SW NETHERLANDS) ON DISTRIBUTION, DENSITY AND BIOMASS OF 5 COMMON MACROBENTHIC SPECIES - SPIO-MARTINENSIS (MESNIL), HYDROBIA-ULVAE (PENNANT), ARENICOLA-MARINA (L), SCOLOPLOS-ARMIGER (MULLER) AND BATHYPOREIA SP

In order to evaluate the impact of the construction of the storm-surge barrier and secondary dams on macrobenthos of the tidal flats in the Oosterschelde (SW Netherlands), changes in distribution, density and b iomass of five common species (Spio martinensis, Hydrobia ulvae, Areni cola marina, Scoloplos armiger and Bathyporeia sp) were analysed. Data on macrobenthos were collected from 1979 to 1989 on five different ti dal flats. Changes in sediment texture and hydrodynamic factors during the construction and after the completion of the coastal engineering project were taken into account. Three severe winters in a row caused more disturbance in the population of the main predator of S. armiger than did the hydrodynamical changes. A temporary prolongation of the e mersion time (in 1986 and 1987) caused a temporary decrease in juvenil e A. marina. But afterwards they still occupy the same 'nursery ground s'. Increased wave action on the edges of the flats probably created n ew niches for Bathyporeia sp. and Spio martinensis, replacing other be nthic species. It is not yet clear what has caused the decline of H. u lvae in many places in the Oosterschelde estuary. Parasitic infestatio n is one of the possibilities.