Zooplankton trophodynamics and spatial patterns in estuarine transition zones

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Ecosystems are considered to be open systems composed of inter-related heterogeneous subunits. These subunits contain food webs that vary in time and whose trophic interactions provide the pathways of energy and matter from lower trophic levels to consumers and predators. At the same time environmental spatial complexity and interconnectivity via active and passive transport processes (e.g., dispersion of organisms, energy transport through resources) are now recognized to alter population and community dynamics and ultimately maintain biological diversity. This research program aims to understand the control of secondary (zooplankton) productivity by considering the degree of trophic connectivity among spatially discrete habitats of the estuarine landscape and how such exchanges vary on a seasonal scale. A number of interrelated short-term goals will be addressed, focussing on particular aspects of tropho-dynamics and habitat connectivity in the estuarine transition zone of St Lawrence Estuary: (1) Seasonal succession of zooplankton assemblages in habitats arrayed along (e.g., salinity) and across (shoal vs. deep habitats) the estuary at different times of the year will be determined. (2) Secondary production by focussing on trophic linkages within species assemblages of various habitat types will be determined. (3) Potential subsidies and the degree of trophic coupling among habitats will be quantified, focussing on a subset of species that play a major role in energy transfer. (4) Rates and strength of trophic linkages will be measured using in situ and laboratory experiments. (5) In the longer term, we aim to develop a coupled biological-physical model to estimate the relative importance of in situ local production and subsidy transport among habitats to overall estuarine secondary production. This research proposes two main projects, one focussing on overall zooplankton production, grazing and predation of zooplankton in the heterogeneous space of the estuarine transition zone. The second one focuses on temporal and spatial variability, its causes and importance of relationships between dominant copepods and intermediate sized predators (mysids) to overall secondary productivity.