CANCELLED - Differential habitat use by two Ponto-Caspian invaders in coastal areas of the Laurentian Great Lakes

Background/Question/Methods

Round goby (Neogobius melanostomus) and dreissenid mussels (Dreissena spp.) are native Ponto-Caspian species that are established, widespread invaders throughout the Laurentian Great Lakes. Round goby is known to consume soft-bodied invertebrates and Dreissena spp. corresponding with ontogenetic habitat shifts. Round goby is expected to be more prolific in habitats primarily dominated by Dreissena because Dreissena is a known facilitator of the round goby. Recently, however, studies have shown that round goby invade coastal areas across various habitat types and may proliferate in areas devoid of Dreissena such as inland coastal lakes. By contrast, pierheads provide ideal habitat for Dreissena colonization which in turn may provide suitable habitat for larger and older round gobies that have undergone ontogenetic diet shifts. We hypothesized that: (1) pierheads, when compared to inland lake habitats, will contain higher densities of Dreissena and such as, a higher abundance of larger and older round gobies, and (2) round goby diet will comprise mostly of Dreissena at pierheads and soft-bodied prey at inland lake habitats. To test our hypotheses, we sampled Dreissena and round gobies at six sites in Lake Michigan (each with pierhead and inland lake habitats). Dreissena were sampled by diving and collecting specimens by hand using six randomly placed quadrats at each habitat. Round goby were sampled using replicate baited minnow traps set overnight.

Results/Conclusions

Mean Dreissena density at pierheads and inland lake habitats was 10,804/m² and 2549/ m², respectively. Two of the six sites, however, had significantly higher Dreissena densities at the inland habitats compared to their adjacent pierheads. Round goby overall catch per unit effort was significantly higher at pierheads compared to inland habitats. Mean total length of round goby at pierheads and inland habitats was 90.2 mm and 69.0 mm, respectively; however, this difference was not significant. Stomach content analysis indicated that soft-bodied prey comprised a larger portion of the round goby diet at pierheads, compared to Dreissena and other hard bodied prey, which was contrary to predictions and suggests that round goby show stronger preferences for soft-bodied prey. Overall, our results suggest that Dreissena and round goby can proliferate in habitats not previously identified as a threat, and therefore have further implications for the species’ habitat use and continued expansion in Great Lakes coastal areas.