Diel, seasonal and ontogenetic variations in the vertical distributions of four marine copepods

Abstract

Diel and seasonal v a n a t ~o n s in the vertical distnbut~ons of Calanus finmarchicus Metrjd~a longa M lucens and C h ~r ~d l u s armatus in Malangen, northern Norway, were determined from F e b ~ uary until December 1992 The vertical behav~our differed among the species and among the ditterent stages of a single species The vertical distnbution of C hnmarchlcus was d o m ~n a t e d by seasonal rather than d ~e l vertical migrat~on, and this species was found in surface waters during the spring phytoplankton bloom (March to May) and at the bottom of the fjord in the fall and wlnter Melrldla spp were generally cons~stent d ~e l vertical mlgrators However M longa usually stayed deeper and had a larger migration dmplltude than M lucens M longa was more deeply dlstrlbuted In the w ~n t e r than d u r ~n g the summer while M lucens showed no such seasonal trend The vertical behaviour of C d ~m a t u s was related to the seasonal change In day length and diel vert~cal ~nlgratlon was strong In periods of large d a y h i g h t contrast (spring and autumn) but ceased d u r ~n g the p e r ~o d s of m ~d n ~g h t sun and wlnter darkness Duiing the summer C armatus stayed d e e p both day and night D ~e l