OCCURRENCE OF BYTHOTREPHES-CEDERSTROEMI (SCHOEDLER 1877) IN LAKE-SUPERIOR, WITH EVIDENCE OF DEMOGRAPHIC VARIATION WITHIN THE GREAT-LAKES

The predaceous cladoceran, Bythotrephes cederstroemi (Schoedler 1877), was first noted in the Great Lakes in late 1984, and had spread to Lakes Huron, Erie, Ontario, and Michigan by late summer of 1986. Zooplankton samples collected from Batchawana Bay, Lake Superior on 15 September 1988 contained large numbers of B. cederstroemi (122.8 individuals/m2). Geographic variation in Great Lakes B. cederstroemi was observed when this sample was compared to samples from Lake Erie. There was a greater percentage of males present in the Lake Superior sample as well as a greater number of females carrying sexual resting eggs. B. cederstroemi from Lake Superior weighed more than those from Lake Erie. These differences are probably the result of physiological responses to different environmental conditions, and not genetic differentiation of B. cederstroemi populations among the Great Lakes. © 1990, International Association for Great Lakes Research. All rights reserved.