COMPARATIVE ANALYSIS OF ST. CROIX RIVER MUSSELS AND HOST FISH SPECIES

Brandon Sansom, Department of Biology, Washington and Jefferson College, Washington PA
Mark C. Hove, Department of Biology, Macalester College, St. Paul MN
Daniel J. Hornbach, Departments of Biology and Environmental Studies, Macalester College, St. Paul MN

The parasitic relationship most North American freshwater mussels have with fish hosts is vital to their reproduction and dispersal. Female mussels release glochidia, microscopic larvae, into the water, often in ways that elicit fish to feed on or brush against them. Glochidia that encounter a suitable host have the ability to metamorphose into juveniles. Some mussel species rely on specific fish species as hosts, while others utilize a wide range of fish hosts. The objective of this research was to determine if variations in mussel population size are correlated to the fish host population size within the St. Croix River. Long-term mussel population data were obtained from Dan Hornbach and Macalester College Department of Biology. Fish population data were obtained from the Minnesota and Wisconsin Department of Natural Resources as well as the Minnesota Pollution Control Agency. The data were then analyzed using JMP 7.0 (SAS Institute.). Comparison among all mussel species and all fish species revealed no strong trends. This was expected since there are 40 mussel species in the St. Croix River, each with different host requirements and host attraction strategies. The same held true when all species of juvenile mussel were compared to all fish species. However, strong trends were observed between mussel species with restricted host requirements and their specific fish host species. The strongest trend in the linkage between fish and mussel density was between Quadrula pustulosa (pimpleback) and Cyclonaias tuberculata (purple wartyback) mussels and their host, members of the catfish family. The pimpleback and purple wartyback peak density seem to have a lag period of three to five years relative to the peak catfish density. Four genera of mussels, Potamilus, Ellipsaria, Truncilla and Leptodea, and their host, the freshwater drum, had strong trends with a lag period of three to five years as well. These trends did not, however, produce any statistical significant results. The frequency of fish and mussel sampling are inconsistent, limiting our ability to accurately calculate lag periods. Additional fish survey data has recently been obtained and we hope to determine whether or not statistically significant trends exist.

References

McMahon, R. F. 1991. Mollusca: Bivalvia. Pages 315-399 in: Thorp, J. H. and A. P. Covich, editors. Ecology and classification of North American freshwater invertebrates. Academic Press, Inc. New York, New York. 911 pp.

Strayer, D. L. 2008. The Monster's Parts: Conservation Implications. Page 118 in: Hauer, F. R. editor. Freshwater Mussel Ecology: A Multifactor Approach to distribution and Abundance. University of California, Berkeley, California. 204 pp.