The benthic macrofauna along the estuarine gradient of the Schelde estuary

The intertidal benthic macrofauna of the Schelde estuary (The Netherlands and Belgium) was sampled in late autumn of 1990 at 50 stations along the whole salinity gradient (between Vlissingen and Dendermonde), including the freshwater tidal part. All stations were situated in sheltered areas with a relatively muddy sediment. Species richness, diversity and total biomass of the benthic macrofauna decreased along the salinity gradient from Vlissingen to Dendermonde, while total density showed no clear trend. Especially the oligoha- line and freshwater tidal part of the Schelde estuary was characterized by a very impoverished benthic community, composed only of Oligochaeta. No other species (freshwater, marine or brackish) was observed in this part of the estuary. The marine part had a more diverse macrozoobenthos structure than that of the brackish part. Species found only in the marine zone are Cerastoderma edule, Tharyx marioni, Eteone longa, Nephtys hombergii and Capitella capitata. In the brackish part of the estuary, Corophium volutator was a typical, dominant species. However, a lot of the dominant species were common in both the marine and brackish part of the Schelde estuary (e.g. Heteromastus filiformis, Pygospio elegans, Nereis diversicolor, Macoma balthica). The observed radient in species composition and dominance is compared with some other European estuaries. The marine and brackish part of the Schelde estuary is quite similar to other european estuaries. The freshwater tidal part, however, was more impoverished.