PHENOLOGY IN CALANUS-FINMARCHICUS - HYPOTHESES ABOUT CONTROL MECHANISMS

Calanus finmarchicus (Gunnerus) stratify narrowly near 500 m depth during their fifth copepodite resting phase in North Atlantic Slope Water off southern New England, USA. They probably achieve this by migration to a specific, daytime isolume. Photoperiod information provided by light intensity at depth could serve as a cue for termination of the resting phase. Population data on tooth formation and gonad growth show that the resting stock prepares for termination in late winter and matures in February-March. Photoperiods are lengthening throughout that seasonal interval, and might cue arousal. An endogenous, 'long-range' timer that cues arousal after an interval of rest is another possible mechanism.