Changes in the summer zooplankton community of the Indiana waters of Lake Michigan inshore at a Michigan City transect, 1987 and 1988

Alterations in the summer zooplankton community that have appeared since Johnson's (1972) study of a Michigan City (site M) transect in southeastern Lake Michigan were investigated. Vertical tows were made at 5, 10, 15, and 18 meters from June through August in 1987 and 1988 in order obtain data that could be compared with that of Johnson (1972).Subsamples analyzed were proportionately larger than those of Johnson (1972), in order to obtain a detailed profile of the species and numbers in the community, and to identify large, predatory zooplankton species that are believed to have been severely impacted by the explosive growth of the alewife population during the 1960's.The most common crustacean species collected were: Diacyclops thomasi, Leptodiaptomus minutus, Leptodiaptomus ashlandi, calanoid and cyclopoid nauplii and copepodids, Daphnia retrocurva, and Bosmina longirostris. The most common rotifer species collected were Keratella c. cochlearis, Keratella crassa, Kellicottia longispina, Conochilus sp., and Polyarthra sp.. Higher numbers of Epischura lacustris adults and copepodids, Leptodora kindti, Mesocyclops edax, Daphnia galeata mendotae, and the rotifers Asplanchna priodonta, Conochilus sp., Keratella crassa, and Ploesoma truncatum were recorded as compared to Johnson's 1972 data. The summer zooplankton community of this transect appears to have been represented in the summers of 1987 and 1988 by a greater number of large crustacean zooplankton species, as opposed to a 1970 community dominated by small microfiltrators and D. thomasi.Department of BiologyThesis (M.S.