Cladoceran Faunas Associated with Aquatic Macrophytes in Some Lakes in Northwestern Minnesota

The cladoceran faunas associated with 12 species of aquatic macrophytes were studied to determine if the Cladocera showed community preference to specific plants. Almost 3,000 specimens belonging to 38 species of Cladocera were counted. Forty—two collections were made in seven lakes near Lake Itasca (N.W. Minnesota). SCUBA was used to select appropriate single—species stands of the 12 plants. When all collections from each species of plant were summed from all seven lakes, some grouping was evident. The cladoceran communities resulted in a breakdown of the plants into five groups. These were broad—leaved submersed, fine—leaved submersed, floating—leaved, Chara, and others. Water depth and sediment type did not seem to determine the distribution of those plant groups that showed specific cladoceran associations. When all cladoceran collections from a single lake were grouped the two limnologically most similar lakes showed quite different cladoceran faunas. Two measurements of community type, namely coefficient of community and per cent similarity, were calculated with the latter giving better results. These measurements supported the hypothesis that aquatic macrophytes control the distribution of the littoral Cladocera.