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Zooplankton samples were collected from 0 to 50 m depth at 2 stations in Jones Sound and 1 in Baffin Bay in August and September of 1983.Levels of chlorophyll and phaeopigment were measured in several stages of Calanus hyperboreus and Calanus glacialis at 4 h intervals, to examine diurnal feeding behavior in copepods which do not vertically migrate on a daily basis.All stages examined for each of the 2 species showed diurnal variations in feeding activity.In addition, different stages and species always started to feed synchronously, although timing of onset of evening feeding was different at each of the 3 stations.On each occasion feeding started when incident light intensity decreased to < 4 W m-2. Cessation of feeding in the morning, however, was not linked to a particular intensity of incident light and may be controlled by satiation of appetite.Levels of 3 digestive enzymes protease, laminarinase, and amylasewere measured in 2 stages of C. hyperboreus and C. glacialis at 4 h intervals over a 48 h time series at the second of the Jones Sound stations.There were no rhythmic changes in amounts of enzymes in any of the stages.Maximum levels of gut pigment within any 1 stage were not necessarily correlated with ambient chlorophyll concentrations, which varied by a factor of 4 among stations.
Head et al. (Tue,) studied this question.