Illinois Natural History Survey - University of Illinois

Introduction of zebra musselDreissena polymorpha and round goby Neogobius melanostomus, two invasive species from the Black/Caspian Sea region, has greatly impacted the Lake Michigan benthic community. The zebra mussel was introduced into the Great Lakes in 1986 and was established in Lake Michigan by 1989.

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.

This study began in summer 2006 and will run through summer 2008. The round goby predation experiment consists of three treatments: 1) round goby access, 2) round goby exclusion, and 3) cageless control (bricks only). We use bricks with the same substrate and surface area to focus specifically on the effects of round goby predation on zebra mussel colonization at each location. Bricks of each treatment will be left on the bottom for 1, 2 or 3 seasons to look at short and long-term effects.