Trophic transfer of organic matter along environmental gradients in an important nursery zone of the St. Lawrence estuary

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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. We propose here to work in the estuarine transition zone of the St. Lawrence estuary, an important nursery zone for fishes that is supported by a high productivity of autotrophic and heterotrophic plankton. However, we still do not completely understand the processes implicated. Since pelagic and benthic food webs are tightly coupled through nutrient and energy flow, our objective is to understand the ecological importance of organic matter transfer within the estuarine food web (pelagic and benthic) by considering the degree of trophic connectivity among habitats of the estuarine landscape and how such exchanges vary on a seasonal scale. To achieve our scientific objective, we request two sampling cruises (June and August 2010), each 7 days, on the research vessel "Lampsilis" that offers the possibility to sample in shallow littoral zones as well as in deeper channels. To cover an important spatial scale our team, composed of researchers and students from UQAR and UQAC, will sample transects along environmental gradients from very shallow bays to channel habitats in two distinct salinity zones of the estuarine transition zone. To trace details of element cycling, we will use stable carbon and nitrogen isotope analyses from particulate organic matter, zoo- and ichthyoplankton as well as benthic macro and meiofauna.