J. Great Lakes Res. 27(2):167–184 Internat. Assoc. Great Lakes Res., 2001 Results from the U.S. EPA’s Biological Open Water Surveillance Program of the Laurentian Great Lakes: III. Crustacean Zooplankton

ABSTRACT. Open water zooplankton communities were sampled across all five Laurentian Great Lakes during spring and summer 1998. Spring communities were characterized by relatively low species numbers and densities. Crustacean communities in all lakes except Lake Ontario were dominated by diaptomid copepods in spring. During summer, both abundance and species richness increased, the latter owing largely to the appearance of populations of cladocerans. Crustacean communities in the upper lakes were dominated by diaptomid copepods, cyclopoid copepodites, and Daphnia galeata mendotae (co-dominant with Holopedium gibberum in Lake Superior), and showed a high degree of spatial homogene-ity. Lake Erie supported a notably more species rich community, and also exhibited a high degree of spa-tial heterogeneity. Lake Ontario differed from the other lakes by its relative lack of calanoid copepods, being dominated instead by cyclopoid copepods, along with Bosmina and Daphnia. There was a clear distinction between community composition in the western and eastern portions of the lake, though the reasons for this are unclear. INDEX WORDS: Zooplankton, cladocerans, copepods, ecology, spatial distribution