The demersal fish and macro-invertebrate assemblages of the Westerschelde and Oosterschelde estuaries: overview and final conclusions

An overview on the nursery function of the Westerschelde and the Oosterschelde estuaries for demersal fish and macro-invertebrates is presented; based on all data sets presented in this thesis. The present thesis provides a baseline, and suggests that both the Westerschelde and Oosterschelde estuaries play a significant role as nursery areas for several demersal fish and macro-invertebrate species. The forcing factors for recruitment and the seasonal appearance of (post) larval fish and macro-crustaceans are explained. Biodiversity is related to habitat use and habitat availability. The faunas of the Westerschelde and Oosterschelde are structured by a limited number of environmental variables, and the prediction of species occurrence by means of single- species logistic models is discussed. Spatial, long-term and seasonal patterns in density in relation to the environment are summarized by means of multivariate analyses and graphical representation of trends per species and per taxonomic group. The seasonal appearance of both (post)larval and juvenile fish and macro- crustaceans in the Westerschelde is described. Density of the commonest species is predicted by means of single- species linear regression models. A short description of the human impact on the fish and macro-invertebrate assemblages is given. In the functional part of this overview, a generalized food web for the Westerschelde is presented; and the importance of mysids as prey for several fish and macro-crustaceans in the Westerschelde is discussed. Finally, 10 major conclusions and some remarks are formulated and some recommendations for future research are given