Illinois Natural History Survey - University of Illinois

Predation May (or May Not) Work to Control Zebra Mussels

Predation by native species as a biological control of invasive species is usually limited. Native predators may not be adapted to utilizing the introduced organisms as forage. Predation on zebra mussels, Dreissena polymorpha, provides a good example of the complex response of natural predators. Soon after their introduction, zebra mussels reached high densities and became strong competitors with lower trophic levels. Several organisms, such as diving ducks, crayfish, eel, common carp, pumpkinseed, European roach, and freshwater drum, have been found to consume zebra mussels. Several other fish species are listed as potential predators of zebra mussels because of their historic consumption of other native molluscs. There is little evidence, however, of whether or not the potential native predators benefit by consuming zebra mussels or if their predation will serve as a biological control. In a study focused on catfish predation on zebra mussels in the Mississippi River, we investigated these relationships with blue catfish (Ictalurus furcatus) and channel catfish (Ictalurus punctatus).

Due to their historic consumption of native mussels, channel catfish were hypothesized to feed on zebra mussels whereas blue catfish were not. We found the occurrence of zebra mussels in the gut to be the opposite of what was expected. Over 65% of the blue catfish sampled had consumed large numbers of zebra mussels, whereas less than 15% of the channel catfish consumed zebra mussels. Furthermore, fish consuming zebra mussels were almost always 200-350 mm in size. We estimated the percent digestion of zebra mussels in the gut and found a great deal of variation in conversion rates. Many mussels pass through the gut and were found completely intact in the intestine. Bioenergetics work is needed to investigate digestive mechanisms because our data suggest that only fish that select exclusively for zebra mussels are successfully utilizing them as prey. It does not appear that any species has been successful in controlling zebra mussels in North American waters. Instead, the response of natural predators to invasive species continues to exceed our knowledge of predator/prey relationships. Additional research is needed to investigate the impact of invasive species and the bioenergetic benefit to native predators.

Randy M. Claramunt, Dave Wahl, Chad Dolan, John Dettmers, and John Tucker, Center for Aquatic Ecology

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