Crayfish Population Boom

From May, 1996 (Update #27)

Crayfish numbers have dramatically increased at a natural, rocky (cobble) reef in southwestern Lake Michigan as a result of the zebra mussel invasion, according to Nancy Tuchman, an Illinois-Indiana Sea Grant-funded researcher. Prior to the 1992 invasion, crayfish (mostly Orconectes propinquus and O. virilis) were sparse (about 0.5/m[2]) in southwestern Lake Michigan, the Loyola University professor said. In 1993, however, crayfish numbers doubled. By 1995, the population had increased twelvefold to six per square meter, about one crayfish every few feet. By filtering the water, zebra mussels have increased the water clarity in Lake Michigan, which has affected the amount of light reaching the reef, Tuchman said. Because the reef received more light, there was an increase in algae and in organisms that eat algae, such as insects. This has led to increases in the number of crayfish, which consume both algae and insects. Tuchman noted she frequently finds crayfish hiding in algae rather than in rock crevices, which is their preferred habitat, because zebra mussels now cover the crevices.

Pat Charlebois, Illinois/Indiana Sea Grant.

ID: 199605-4.

The Zebra Mussel Update was a 4- to 8-page quarterly national newsletter published by the University of Wisconsin Sea Grant Institute from May 1990 through May 1997. The ZMU documented the spread of the zebra mussel -- an exotic nuisance mussel -- through North America's freshwater environments, especially the Great Lakes, and on efforts to control it.