ZEBRA MUSSEL (DREISSENA-POLYMORPHA) EFFECTS ON SEDIMENT, OTHER ZOOBENTHOS, AND THE DIET AND GROWTH OF ADULT YELLOW PERCH (PERCA-FLAVESCENS)IN POND ENCLOSURES

Zebra mussels (Dreissena polymorpha) in enclosures located in an exper imental pond adjacent to Lake St. Clair, Michigan, increased sedimenta tion rate but had relatively minor effects on percent organic matter a nd percent nitrogen content of sediment. In contrast, sediment from La ke St. Clair adjacent to zebra mussels was significantly higher in car bon than that 0.5 m away. Zebra mussels increase the nutritional value of surficial sediment and provide greater structural heterogeneity, w hich is probably more important in causing change among zoobenthos. Zo obenthos and yellow perch (Perca flavescens) diet were dominated by di pteran larvae and leeches. Zoobenthos was significantly different betw een enclosures with and without zebra mussels. Treatments with zebra m ussels had significantly more oligochaetes and tended to have more cru staceans (isopods and amphipods). In June, yellow perch without zebra mussels consumed significantly more zooplankton, and those with mussel s had more crustaceans in their diet. Zooplankton density was greater in treatments without zebra mussels. Yellow perch with zebra mussels g rew significantly more than those without mussels. Zebra mussels in th e enclosures neither reproduced nor were eaten by yellow perch; hence. the observed growth differences were due to indirect effects involvin g zebra mussel induced changes in benthic structure and biota.