Relationships among round gobies, Dreissena mussels, and benthic algae in the south nearshore of Lake Ontario

Abstract

Round goby (Neogobius melanostomus) populations are established in all the Great Lakes, subsequent to the success of the Dreissena mussel invasion. Additionally, localized resurgence of the nuisance alga, Cladophora glomerata, also has been reported across several of the Great Lakes post-Dreissena. We examined the relationship among round goby size and population density and Dreissena mussel metrics and Cladophora biomass in three regions of the nearshore environment of U.S. waters of Lake Ontario during summer 2008. We also estimated the size of the round goby population in these regions. Correlations between round goby population metrics and Dreissena mussel metrics suggest a low potential for lakewide control of mussel populations by round gobies. In August but not June, fish density was positively correlated with Dreissena density, biomass, and size, suggesting round gobies did not depress mussel numbers, but may selectively remove some smaller mussel size classes. Round goby length was positively correlated with Cladophora biomass, which probably is best explained as a sampling artifact. Seasonal changes in the round goby population density with depth were suggestive of an offshore migration in late summer. Fish were generally smaller but equally abundant, moving west-to-east along the nearshore environment of the lake. We estimated that the nearshore population size of round gobies was 0.7billion fish, equivalent to 2.2 fish/m2. This translated into approximately 1287tonnes of round gobies or about 40kg/ha. Coupled with the broad diet selection of this invasive fish, results suggest that round gobies will have a substantial impact on the structure of the nearshore benthic community.