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Tuesday, January 30 • 4:00pm - 4:20pm
ASIAN CARP & OTHER AQUATIC INVASIVES: Stable Isotopes Indicate Zebra Mussels (Dreissena polymorpha) Increase Dependence of Lake Food Webs on Littoral Energy Sources

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AUTHORS. Brian R. Herwig, Minnesota Department of Natural Resources; Margaret C. Thompson, University of Saint Thomas; Kyle D. Zimmer, University of Saint Thomas; Ryan S. Trapp, University of Saint Thomas; Claire E. Herzog, University of Saint Thomas; Catherine E. Hegedus, University of Saint Thomas

ABSTRACT. We assessed impacts of zebra mussels on energy flow by comparing two Minnesota lakes. Lake Carlos has a dense population of zebra mussels, while upstream Lake Ida was free of zebra mussels until 2014 and densities remained extremely low during our study. We used 13C and 15N stable isotopes to assess patterns of energy flow as d13C and d15N values differ in organisms supported by phytoplankton production (lower 13C, higher 15N) relative to organisms supported by littoral energy sources, such as periphyton and benthic algae. We used both traditional mixing models and a Bayesian mixing model to estimate and compare percentages of littoral vs. pelagic energy sources supporting various fish species present in Carlos and Ida lakes. Preliminary results indicate that percentage of littoral energy sources was significantly higher in Lake Carlos compared to Lake Ida for nearly all fish species analyzed. Effect size was often large, with reliance on littoral energy by some fish species approximately two-fold higher in the presence of zebra mussels. We posit that this greater reliance on littoral energy sources in the Lake Carlos food web is likely driven by high zebra mussel densities reducing phytoplankton abundance. Subsequent reductions in zooplankton likely force remaining consumers to shift diets towards littoral food sources.

Tuesday January 30, 2018 4:00pm - 4:20pm CST