Monday, June 4, 2007 - 3:30 PM
50

Food Web Dynamics of Fishes in Relation to Lateral Connectivity Gradients in the Upper Mississippi River

Katherine A. Roach, University of Kansas, Kansas Biological Survey, 2101 Constant Avenue, Higuchi Hall, Lawrence, KS 66047, James H. Thorp, PhD, Ecology and Evolutionary Biology, University of Kansas, 2101 Constant Avenue, Lawrence, KS 66047-3759, and Michael D. Delong, Large River Studies Center, Winona State University, Biology Department, Winona, MN 55987.

Structurally complex rivers consist of the main channel and various slackwater habitats which differ in hydrological connectivity within the riverscape. Differences in current velocity and other factors alter abiotic and biotic conditions along lateral gradients from main channels to backwaters. Our study focused on the importance of lateral connectivity gradients in structuring aquatic food webs in the Upper Mississippi River.  We used stable isotope analysis (N and C) of molluscs and fish as well as fish stomach content analysis to determine patterns of trophic position in herbivorous molluscs and five feeding guilds of fish. Over 1000 tissue samples were taken in four lateral sites (main channel, secondary and tertiary channels, and backwaters) in each of two reaches of two river “pools” during June and August of 2004.  Statistical analysis show that food web complexity and composition varied laterally in all reaches, and trophic position was highest at intermediate to low hydrological connectivity.  These results suggest that areas with intermediate to low connectivity form habitat patches with low levels of disturbance and high levels of resources.  While physical forces dominate trophic interactions in the main channel, biological interactions may control food web dynamics in backwaters and various low-flow, lateral channels.

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