Pelagic Occurrence of Benthic Animals Near Shore in Lake Michigan

Collections with towed nets showed that presumably sedentary benthic animals occurred continually in the water above bottom in small numbers over depths of 6 m and 9 m in southeastern Lake Michigan. Densities were usually higher at night and in the months from June through September. Pelagic individuals at both depths consisted mainly of two chironomids, Saetheria tylus and Chironomus sp., and two naidids, Stylaria lacustris and Nais pardalis, but a total of 71 species were collected over a seven-month period. About 0.1% of the benthic animals were present above bottom at any time during a night in July 1974. The dominant pelagic species were the same as the benthic dominants at 6 m, but were much less important in the benthos at 9 m. We propose that this behavior, analogous to drifting of stream invertebrates, serves to maintain benthic populations in the frequently disturbed sediments of shallow (6 m deep or less) areas in Lake Michigan, and probably many other large lakes.