The Effects of Predation and Unionid Burrowing on Bivalve Communities in a Laurentian Great Lakes Coastal Wetland

After the dreissenid mussel invasions of the Great Lakes, unionid densities declined dramatically, but the reasons are not well understood. Predation and unionid burrowing were studied in a wetland of western Lake Erie in 2001-02. Experiments to restrict molluscivore access with exclosures of two mesh sizes showed that smaller mesh exclosures had higher dreissenid, sphaeriid, and Corbicula flumineaclam numbers than larger mesh exclosures or open controls had. Dreissenids were more abundant on C. fluminea in small mesh exclosures than in large mesh exclosures or uncaged controls. In another test, two unionid species were held in exclosures with either 5 cm, 10 cm, or 20 cm deep sediments. Fewer dreissenids were found on Leptodea fragilis than on Pyganodon grandis shells, but dreissenid numbers on P. grandis and Quadrula quadrula shells were similar. Attached dreissenid numbers and sphaeriid and C. fluminea densities were higher inside than outside exclosures. Dreissenids attached more often to unionids that could burrow below the deep sediments than to shallow-burrowing mussels. Molluscivore presence may be important for limiting bivalve numbers in wetland habitats.