Effect of daylength and food concentration on in situ diurnal feeding rhythms in Arctic copepods

Abstract

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^-.