NEKTON COMMUNITIES OF AN INTERTIDAL CREEK OF A EUROPEAN ESTUARINE BRACKISH MARSH

The utilization of an estuarine brackish marsh in the Westerschelde es tuary (southwest Netherlands) by fish and crustaceans visiting the int ertidal creeks at rising tides was investigated over an 18 mo period. Samples were collected every month over a tidal cycle. A stow net pass ively fished the nekton migrating in and out of the marsh habitat. Sim ultaneous measurements of current speed and waterheight allowed for qu antification of the catches. Multivariate clustering and ordination te chniques were applied to assess temporal changes in the nekton assembl age. A total of 68 fish and crustacean species were caught but only 38 were regular visitors of the marsh creek. The marsh nekton community proved to have a very stable character. Only 40% of the observed varia nce could be explained. The seasonal appearance of juvenile stages of fish and crustaceans was found to differentiate between spring and sum mer-autumn communities. The environmental variables measured (i.e. tem perature, salinity, oxygen concentration and detritus standing stock) did not correlate well with the observed changes in community structur e. The mysid shrimp Neomysis integer dominated the community, both in density and biomass, during most of the year. Early postlarval flounde r Pleuronectes flesus characterized the spring nekton assemblage. Earl y postlarval brown shrimp Crangon crangon was abundant from spring thr ough autumn. In late summer juveniles of seabass Dicentrarchus labrax, common goby Pomatoschistus microps and shore crab Carcinus maenas wer e typical members of the marsh creek nekton. The hyperbenthic fauna of the marsh was comparable to the hyperbenthos found in the adjacent su btidal parts of the Westerschelde estuary while the epifauna of both a reas differed substantially. It is argued that the marsh under study i s a nursery ground for only a small number of estuarine inhabitants: C . crangon, P. flesus, C. maenas, P. microps, D. labrax and possibly 2 mullet species. Adult flounder, adult and juvenile common goby, juveni le seabass and the early postlarval brown shrimp all use the creeks as feeding ground, mainly preying upon the creek infauna and mysids. Giv en the high abundance of hyperbenthic mysid shrimp in the marsh and th eir presumed role in detritus-based food chains, we believe marsh stud ies should not refrain from considering this component of the nekton. This is the first study reporting on the nekton use of a European mars h. The need for similar research in other European marshes is stressed .