Mortality of zebra mussel, Dreissena polymorpha, veligers during downstream transport

1. Streams flowing from lakes which contain zebra mussels, Dreissena polymo rpha, provide apparently suitable habitats for mussel colonization and down stream range expansion, yet most such streams contain few adult mussels. We postulated that mussel veligers experience high mortality during dispersal via downstream transport. They tested this hypothesis in Christiana Creek, a lake-outlet stream in south-western Michigan, U.S.A., in which adult mus sel density declined exponentially with distance downstream. 2. A staining technique using neutral red was developed and tested to disti nguish quickly live and dead veligers. Live and dead veligers were distingu ishable after an exposure of fresh samples to 13.3 mg L-1 of neutral red fo r 3 h. 3. Neutral red was used to determine the proportion of live veligers in sam ples taken longitudinally along Christiana Creek. The proportion of live ve ligers (mean +/- SE) declined from 90 +/- 3% at the lake outlet to 40 +/- 8 % 18 km downstream. 4. Veligers appear to be highly susceptible to damage by physical forces (e .g. shear), and therefore, mortality in turbulent streams could be an impor tant mechanism limiting zebra mussel dispersal to downstream reaches. Predi ctions of zebra mussel spread and population growth should consider lake-st ream linkages and high mortality in running waters.