On the Population Biology and Nature of Diapause Oflabidocera Aestiva(copepoda: Calanoida)

The calanoid copepod, Labidocera aestiva was collected from Vineyard Sound, Massachusetts between July and December 1978. Adult size (cephalothorax and total body length) was inversely proportional to surface water temperature at the time of collection. The major switch from subitaneous to resting egg production occurred during late August to early September, but a small percent of subitaneous eggs continued to be produced throughout the fall. Resting eggs were cold-resistant and when chilled at 5° C hatched synchronously when warmed to 21° to 23° C. Individual resting eggs kept continuously at 19° C took longer to hatch and emergence was asynchronous. The resting eggs of L. aestiva appear to be in a state of diapause similar to many insects, and it is suggested that photoperiod is the primary cue inducing the production of resting eggs.