Effects of Variation in River Discharge and Wind-Driven Resuspension on Higher Trophic Levels in the Mobile Bay Ecosystem

James H. Cowan, Jr.1, John F. Valentine2 and William M. Graham2 1 Department of Marine Sciences, University of South Alabama, Mobile, AL    36688 2 Dauphin Island Sea Lab, 101 Bienville Boulevard, Dauphin Island AL 36528

Proper management of the Mobile Bay estuary and its living resources requires a fundamental understanding of current ecosystem structure and function. In addition, knowledge of how the ecosystem responds to natural and human-induced perturbations is necessary for predicting ecosystem health in the future. Among the most important aspects of how estuarine ecosystems function are the linkages between nutrient delivery, primary production and secondary production. More specifically, we do not fully understand how these linkages are modulated by variability in freshwater discharge in an adjacent estuary--estuarine plume/shelf ecosystem. We argue that understanding is lacking because adjacent systems have seldom been studied at appropriate temporal and spatial scales, due largely to difficulty in finding a location where study is logistically feasible. Mobile Bay and vicinity offers such a location. The information collected during this study will provide insight as to how pulsed delivery of freshwater to estuaries acts to regulate production because we will be able to investigate trophic linkages across a spatial scale that has been heretofore impracticable. In this initial phase, efforts will be focused on characterization of the biological and biogeochemical patterns and pathways within the study area. Three major research questions guide this work: 1) What are the nutrient stocks, and what is the size of the biomass pool at each trophic level (e.g. microbial, phytoplankton, zooplankton, benthos, and forage fishes), and how do they change in space with each season?; 2) At what rate is biomass (carbon) transfered between pools; and, 3) Do transfer rates and transfer pathways between biomass pools differ withvarying levels of freshwater inflow, during wind driven resuspension events, and with season?