PARENT SESSION
Poster Session # 22: Late-Breaking Newsworthy Posters
Friday, August 8 Presentation from 8:30 AM to 10:00 AM. SITCC Exhibit Hall B.
Trophic position of planktivorous fishes altered by the invasive bivalve, Dreissena polymorpha: A stable isotope study.
Wilson, Alan*,1, Knoll, Lesley2, Montoya, Joseph1, Sarnelle, Orlando2, Hamilton, Stephen3, Hay, Mark1, 1 Georgia Institute of Technology, Atlanta, Georgia, 303322 Michigan State University, East Lansing, Michigan, 488243 Michigan State University, Hickory Corners, Michigan, 49060
ABSTRACT- To determine if the invasive bivalve, Dreissena polymorpha, affects the trophic positioning of lake fishes, we determined the natural abundance of 13C and 15N of phytoplankton, zooplankton, and fish collected from fourteen lakes in Michigan, half of which have been invaded by Dreissena. Trophic position was estimated for each fish from all lakes using the following equation; [2 + (fish 15N − zooplankton 15N − (zooplankton 15N − phytoplankton 15N))÷3]. Between 1 to 4 fish per available species were analyzed from each lake, and prior to our trophic position calculations, fishes were grouped into the following functional categories based on known feeding preferences and total length: (1) Piscivores: largemouth bass and crappie and (2) Planktivores: bluegill, green sunfish, pumpkinseed, darter, minnow, shiner, yellow perch, alewife, and young-of-the-year smallmouth bass. Mean trophic position for each fish species within each lake was calculated, and these estimates were used in later analyses. The trophic position of planktivores was significantly higher in invaded (mean = 2.7, SE = 0.2) than uninvaded (mean = 1.8, SE = 0.2) lakes (P = 0.007). In contrast, there was no difference in the estimated trophic position of piscivores (invaded lakes, mean = 2.9, SE = 0.4; uninvaded lakes, mean = 2.7, SE = 0.3, not different at P = 0.70). The trophic positions of both fish groups were near expectations in uninvaded lakes, but not in invaded lakes. Although the mechanism leading to this shift in apparent trophic position of planktivores in invaded lakes is unclear, it may reflect: (1) dietary shifts by planktivorous fishes due to competitive or predatory reduction of zooplankton populations by Dreissena, (2) changes in the isotopic partitioning of nitrogen by zooplankton due to resource competition with Dreissena, and (3) changes in the isotopic partitioning of nitrogen by planktivorous fishes in invaded lakes. Mechanisms 2 and 3 imply a fundamental change in the overall efficiency of transfer of nitrogen up the food web in invaded lakes relative to uninvaded lakes.
Key words: Dreissena polymorpha , zebra mussels, stable isotopes, food chain length