REDUCED SURVIVAL AND FITNESS IN NATIVE BIVALVES IN RESPONSE TO FOULING BY THE INTRODUCED ZEBRA MUSSEL (DREISSENA-POLYMORPHA) IN WESTERN LAKE ERIE

Fouling by the recently established zebra mussel (Dreissena polymorpha ) causes differential effects among bivalve communities. In 3-mo exper iments and surveys conducted in western Lake Erie during 1990, two nat ive bivalves, Lampsilis radiata and Amblema plicata, showed consistent differences in mortality and biochemical indices of fitness in respon se to fouling by D. polymorpha. Lampsilis radiata was very sensitive t o fouling, experiencing high mortality and reduced fitness in experime nts and natural populations. In field experiments, female L. radiata s uffered higher mortality and lower fitness than males. Amblema plicata was less sensitive to fouling; fitness was reduced in experimentally fouled A. plicata, but mortality and fitness in natural populations we re not affected by D. polymorpha. Six species of native bivalves showe d marked differences in mortality rates at three sites surveyed in wes tern Lake Erie. Mortality was higher in the subfamilies Anodontinae an d Lampsilinae (including L. radiata) than in Ambleminae (including A. plicata) at all three sites, suggesting that differences in life histo ry strategy and shell morphology among subfamilies may be responsible for differential responses to fouling. These data suggest that fouling by D. polymorpha will result in profound changes in native bivalve co mmunity structure.