Physiological energetics of Lake Erie dreissenid mussels:: a basis for the displacement of Dreissena polymorpha by Dreissena bugensis

I measured respiration, shell growth, body mass, and reproduction in sympatric populations of zebra (Dreissena polymorpha) and quagga (Dreissena bugensis) mussels in western Lake Erie to determine if the species differ in physiological parameters and if any differences provide an explanation for the recent displacement of zebra mussels by quagga mussels. Between May and August, I measured respiration (1998), shell growth of marked mussels suspended in cages in the lake (1999-2000), soft body mass and mass of gametes released (1998-2001), and the Dumber of gametes released by individual mussels (1999). Quagga mussels had lower respiration rates and greater shell growth and body mass. There was no difference in the percentage of spawning mussels or the number of sperm released by individuals, but zebra mussels generally released more eggs and a greater mass of gametes than did quagga mussels. Similar reproduction at a lower body mass indicates that zebra mussels devote a greater proportion of body tissue to reproduction. Lower respiration rates and larger size give quagga mussels a competitive advantage and may explain their displacement of zebra mussels.