Fish and crustacean response surfaces to environmental gradients in the Westerschelde estuary (poster)

The probability of occurrence of eleven fish and three crustacean species in the Westerschelde as a response to several environmental variables is predicted. Single logistic regression provides good descriptions of the occurrence along one environmental variable, which is related to the maximum likelihood of presence in the field. Multiple (fractional polygonal and factorial) logistic regressions give insight into the relative importance of each environmental variable. For all 14 species the predictions were relatively successful (60 to 90 percent correctly predicted) by combining data on salinity, temperature, turbidity and/or oxygen. However, these response surfaces should not be interpreted as physiological limits but as actual distribution patterns as a function of these abiotic variables. The addition of other variables such as current velocity, chlorophyl a, SPM or mysid density did not improve the predictions. The models are cross-validated internally and evaluated with a limited data set from the adjacent Oosterschelde

Application of the Westerschelde response models to fish and macro-crustacean data from the Oosterschelde

The aim of this study is to test the applicability of the statistical models, which were developed to predict fish and macro-crustacean responses to the environmental conditions in the Westerschelde estuary (Chapter 6). For this, a data set from the Oosterschelde was used. The probability of occurrence and the prediction of abundance of several dermersal fish and macro-crustaceans in reponse to four environmental variables (salinity, temperature, dissolved oxygen concentration and turbidity) are investigated. The present study can only be seen as a preliminary attempt to validate the robustness of the models that were established for another system. The diagnostics (% correctly predicted; sensitivity and specificity) for the 15 presence absence models based on the Oosterschelde data were comparable to the diagnostics based on the Westerschelde data. Only the models that explained >45% of the variance in density for six species in the Westerschelde, were applied to the density data from the Oosterschelde. These were largely successful when temperature was the main forcing variable (e.g. for Sprattus sprattus and Pomatoschistus microps). The constant high salinity in the Oosterschelde is a favorable condition for Carcinus maenas and Liocarcinus holsatus, partially masking the effect of the other environmental variables in these models. Limanda limanda and Pomatoschistus minutus have different seasonal distribution patterns in both systems. In the Westerschelde both species only occurred during a relatively short period; while in the Oosterschelde they were present throughout the year. This shows the difficulty of applying statistical models from a real estuary to a different type of ecosystem, namely a marine bay like the Oosterschelde

Introduction: objectives and outline of the thesis

The thesis focuses on the nursery function of the Westerschelde and Oosterschelde estuaries for demersal fish and macro-invertebrate species. The main aim of the thesis is to provide a baseline about the higher trophic levels for future process studies in the Delta area. More specifically, both structural and functional patterns in several population parameters (density, biomass, growth, biodiversity, Jood and feeding behaviour) are investigated at community and species levels, and at different temporal (short-, mid- and long-term) and spatial (between and within estuaries) scales. This introductory chapter gives a general description of the epibenthic assemblages and a short overview of the factors on which the nursery function of a system depends. The study area is described and the major engineering works in the Delta area are summarized. An overview of the different sampling methodologies and of the available and used datasets is given. This chapter finishes with the main objectives and an outline of the thesis

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

Asymptotic adaptive bipartite entanglement distillation protocol

We present a new asymptotic bipartite entanglement distillation protocol that outperforms all existing asymptotic schemes. This protocol is based on the breeding protocol with the incorporation of two-way classical communication. Like breeding, the protocol starts with an infinite number of copies of a Bell-diagonal mixed state. Breeding can be carried out as successive stages of partial information extraction, yielding the same result: one bit of information is gained at the cost (measurement) of one pure Bell state pair (ebit). The basic principle of our protocol is at every stage to replace measurements on ebits by measurements on a finite number of copies, whenever there are two equiprobable outcomes. In that case, the entropy of the global state is reduced by more than one bit. Therefore, every such replacement results in an improvement of the protocol. We explain how our protocol is organized as to have as many replacements as possible. The yield is then calculated for Werner states.Comment: 11 pages, 5 figures, RevTeX