Round goby predation on Dreissena in coastal areas of eastern Lake Michigan

Predator-prey interactions between round goby (Neogobius melanostomus) and Dreissena are an important component of the food web in their invaded range in North America and Europe. We conducted two experiments to test the effect of round goby predation on Dreissena in coastal lakes connected to eastern Lake Michigan, USA. First, we conducted a density gradient experiment using 1-m ² cages stocked with 0 to 15 large round gobies (individuals > 7.5 cm total length (TL)). Presence of large round gobies significantly reduced Dreissena densities in all cages. Second, we conducted an exclosure experiment (treatments: none, 6-mm, and 24-mm mesh) in four coastal lakes in littoral habitats. Excluding large round gobies did not significantly affect Dreissena densities in any of the lakes, although we did find a significant effect of excluding large-bodied (i.e., animals larger than adult round goby that cannot pass through 24-mm mesh) predators in one lake. In combination, our two experiments showed that the strength of predator-prey interactions between round goby and Dreissena can vary with location and/or conditions. We hypothesize that the strength of predator-prey interactions between round goby and Dreissena vary spatially across the aquatic landscape depending on habitat (e.g., rocky vs. sandy substrates), which is critical for understanding foodweb dynamics, especially in areas where the round goby and Dreissena are invasive.