Variation in Round Goby Feeding Interactions in Near-Shore Lake Michigan Based on Three Trophic Indicators

Understanding trophic interactions of non-native species is key to elucidating their potential ecological role in newly-invaded ecosystems. The Great Lakes region has long been characterized by a high rate of invasive species establishment. Round Goby (Neogobius melanostomus ) were first detected in Lake Michigan in 1994, and have since increased dramatically in abundance. While past studies of Round Goby in Lake Michigan have primarily focused on specific regions and habitats, Lake Michigan is a large, diverse system and Round Goby trophic interactions may vary across regions and over time. During May, July, and September 2010-2011, we collected Round Goby (via 2-hr bottom set, micromesh gillnets) and their potential benthic invertebrate prey at ten sites throughout much of Lake Michigan. In the laboratory, we identified and enumerated diet contents and potential prey items, and homogenized gobies for subsequent fatty acid and δ 13 C and δ 15 N stable isotope quantification. These three trophic indicators provide complementary information regarding trophic interactions. Diet content analysis and stable isotope analyses are well-established approaches and provide detailed quantification of recent (i.e. short term) prey consumption and long-term indexing of production pathways, respectively. In contrast, fatty acid analysis is a relatively novel method for describing trophic interactions over an intermediate temporal scale. Results indicate diets, fatty acids, and stable isotope signatures of gobies vary individually (by size), seasonally, and spatially. Specifically, the three trophic indicators collectively indicate that Round Goby display a greater reliance on near-shore benthic pathways in western Lake Michigan versus a greater reliance on pelagic pathways in eastern Lake Michigan. This spatial pattern may reflect differential prey production related to physical processes and substrate, i.e., relatively high frequency of upwelling events and preponderance of rocky substrate in western Lake Michigan versus downwelling events and predominately sandy substrate in much of eastern Lake Michigan