Stable isotope analysis : resolving a complex Georgia salt marsh food web, and implications for the management of an invasive species
DeCurtis, Charles Nicholas
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Natural abundance stable isotope values and their distribution reflect physical and metabolic processes within ecological communities. Our knowledge of ecology in the Southeastern United States has increased significantly over the past few decades but lack of critical, such as detailed trophic structure/relationship data, information needed to understand, conserve, and protect natural resources has hampered our ability to effectively manage and conserve ecosystems. My research focused on utilizing stable isotope analysis to describe trophic connections in a Georgia salt marsh ecosystem and to apply the technique by combining statistical models with stable isotope analyses to track and determine area of origin for an invasive species in Georgia, the flathead catfish, Pylodictis olivaris. I examine the food web of a saltwater marsh creek on Sapelo Island. Using natural abundance of stable carbon and nitrogen isotope ratios, I attempt to describe food web interactions from both a connectance viewpoint as well as a detailed trophic organization viewpoint. Also, I amended the creek over a 40 day period with an enriched nitrogen salt (Ammonium chloride) to examine trophic linkages that have been problematic due to small, sometimes indiscernible shifts from one trophic level to the next. I investigated the applicability of natural abundance values of carbon and nitrogen isotopic ratios in muscle tissue to identify the river of origin of Flathead Catfish, Pylodictis olivaris, from the southeastern United States. Catfish were sampled by electrofishing in the Altamaha and Satilla Rivers during the summer of 1998 and 1999. Based on a cluster analysis of isotope values and length, and biology (feeding biology and gape limitation and reproductive maturation), the fish were grouped into 2 size classes within each river (< 550mm and >= 550 mm). This study demonstrates the utility of using isotopic ratios of tissue samples taken from creel specimens to accurately classify fish to their river of origin.