This study cataloged the current taxonomic composition and distribution of crustacean zooplankton at 12 locations in the western arm of Lake Superior during May and August 2001. Zooplankton were last surveyed to this taxonomic level in the western arm in 1973, prior to a number of biotic changes to the lake. Notable differences in the 2001 zooplankton assemblage compared to historical conditions include the establishment of the exotic Bythotrephes longimanus, declines in the density of Daphnia retrocurva and Bosmina longirostris, and an increase in density of Holopedium gibberum. These changes are consistent with an increase in invertebrate predation and similar to changes reported after B. longimanus invasions elsewhere in North America, but a cause and effect relationship is correlative. Densities and body lengths of Lake Superior B. longimanus were within the ranges reported for other Great Lakes.
Bibliographical noteFunding Information:
We thank Mike King and the crew of the R/V Blue Heron for assistance with fieldwork, and two anonymous reviewers who improved the clarity of the manuscript. M. Zhou and D. Wu provided the temperature and Chl a data. This research was funded by a grant from the Minnesota Sea Grant College Program to M. Zhou, N. Wattrus, and D. K. Branstrator; and by a Grant-in-Aid award to D. K. Branstrator from the University of Minnesota.
- Bythotrephes longimanus
- Lake Superior