Occurrence of a Resting Stage in Cyclopoid and Harpacticoid Copepods in Nearshore Lake Michigan

Temporal and spatial differences in the abundance of dormant harpacticoid and cyclopoid copepods in a nearshore area of southeastern Lake Michigan are described. Core samples were taken at three depths (11, 17, and 23 m) at monthly intervals from May to November 1976–79. All dormant harpacticoids were Canthocamptus robertcokeri or Canthocamptus staphylinoides, and all dormant cyclopoids were stage IV copepodids, likely Diacyclops thomasi. The percentage of Canthocamptus and copepodids IVfound in the resting state declined dramatically with increased sampling depth. Dormant Canthocamptus were most abundant in late summer/fall in each of the four sampling years. During this period, usually over 50% of all Canthocamptus were found in the dormant condition. Dormant cyclopoids were most abundant between June and September, but exact seasonal patterns varied from year to year. Factors initiating the dormant condition are not clear, but water temperatures and day length may be important environmental cues. Some of the spatial and year-to-year differences in the proportion of dormant individuals appeared related to variations in the amount of surface detritus. This is the first report of a resting stage in the life cycle of cyclopoids in the Great Lakes.