With their rapid colonization rates, zebra mussels have caused declines of native bivalves and other invertebrate species. Round goby were first found in Lake Michigan in the mid 1990s (Charlebois et al. 2001). Round gobies are a bottom dwelling fish with molariform teeth, which allow them to crush shells (Ray and Corkum 1997); thus mollusks are an important part of their diet (Jude et al. 1992). Round gobies, especially those larger than 7 cm, prey heavily on zebra mussels (Ray and Corkum 1997). A single round goby can consume over 100 juvenile zebra mussels (1-4 mm) per day (Ghedotti et al. 1995). The interaction of these two invasive species has the potential to negatively impact native invertebrates and influence food web dynamics on rocky nearshore areas in Lake Michigan.
During SCUBA sampling, we have observed a striking difference in zebra mussel density on two rocky structures in southern Lake Michigan. An artificial reef of granite rock near Chicago (south) has extremely limited zebra mussel coverage, whereas rock rip-rap covering a water intake line near Waukegan Harbor (north) is completely covered by well established adult zebra mussel colonies. Round goby abundance is much higher on the south structure then on the north structure. Unlike our north study site, which already had established zebra mussel colonies before round goby arrived, the artificial reef was barren when placed in an environment with abundant round goby. This set of circumstances creates a unique opportunity to investigate the dynamic between zebra mussel colonization and round goby predation as a potential deterrent of zebra mussel expansion. We hypothesize that round goby may be able to consume the majority of settled zebra mussels on the south reef before they reach maturity or a size too large for round goby to eat, thus controlling the establishment of zebra mussels. This study can help determine how the interaction of these two species affects each other and the native benthic community, and consequently other organisms higher in the food chain.