Heat-Related Zebra Mussel Mortality in Lake Dardanelle, Arkansas

Baker, W. P., J. N. Stoeckel, and C. J. Gagen, Arkansas Tech University, Fisheries and Wildlife Biology Program, Russellville, AR 72801

Zebra mussels (Dreissena polymorpha) are exotic bivalves known to cause limnological changes in North American freshwater systems. They first were discovered in Lake Dardanelle, Arkansas in 1992. We have sampled veliger, juvenile, and adult stages of zebra mussels in the lake since 1993. The population grew exponentially, reaching a maximum mean density of 7,302/m² in 1997 prior to a heat-related die-off in July of that year that resulted in an estimated mortality of 80%.  Another heat-related die-off in the summer of 1998 resulted in mortality of approximately 90% of the remaining population.  In 1999, zebra mussel densities were much lower than the previous two years with a mean density of 344/m² . We have also sampled turbidity and Secchi disk visibility biweekly. Changes in these parameters correlated with changes in zebra mussel densities. As the zebra mussel population increased in density, we observed a gradual decrease in turbidity and an increase in Secchi disk visibility. Mean turbidity for 1997, the year of maximum zebra mussel density, was 14.5 NTU, the lowest during the seven year sample period. Secchi disk visibility was greatest in 1997 with a mean of 77.6 cm. After the die-off in 1997,
turbidity gradually increased and Secchi disk visibility decreased. In northern climates, populations of zebra mussels are cyclic due to die-offs of older cohorts, but this does not seem to be the case in southeastern reservoirs such as Lake Dardanelle. In these reservoirs, exponential increases in number of zebra mussels occur in years with relatively cool summer water temperatures, and massive die-offs occur when water temperatures remain above 30^o C in excess of one week. Thus, in
shallow southern reservoirs we can expect boom and bust cycles in zebra mussel populations, and that the magnitude of limnological and ecological impacts caused by zebra mussel infestation will fluctuate with size of the zebra mussel population.

Copyright © 1999
Texas Chapter of the American Fisheries Society
Last modified: 03/03/04 04:15:38 PM