DIEL VERTICAL MIGRATION BEHAVIOR OF CALANUS-HYPERBOREUS AT TEMPERATE LATITUDES

Samples historically collected and analysed by the Continuous Plankton Recorder survey in the North Atlantic and adjacent seas were used to examine temporal patterns in the near-surface abundance of copepodite stages V and VI Calanus hyperboreus (n = a total of 32836 samples; mea n latitude of samples = 54 degrees N, SD = 6.7 degrees). The occurrenc e of CV and VI C. hyperboreus was largely restricted to samples collec ted in April, May and June. During this period there was a diel cycle in near-surface abundance which was consistent with a normal pattern o f diel vertical migration. For example, CV-VI C. hyperboreus were 1.9 times more abundant at night than during the day, a difference which w as highly significant (t-test, t(5072) = 3.9, P < 0.001). The ratio of night:day abundance was similar in CV-VI C. finmarchicus (night:day a bundance = 1.4), but markedly higher in CV-VI Metridia lucens (night:d ay abundance = 12.3) and CV-VI M. longa (night:day abundance = 15.0).