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Abstract
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Recent progress in the study on vertical partitioning, ontogenetic vertical migration and life cycles
of meso- and bathypelagic copepods in the western subarctic Pacific is reviewed from the viewpoint of
prey-predator interactions. Gaidius variabilis and Pleuromamma scutullata are particle feeders, and their spawning seasons were well synchronized with that of the phytoplankton bloom. Judging from their vertical distribution depth (G. variabilis; 600-1500 m, P. scutullata; 200-600 m), it is suggested that they are depending on directly sinking particles from the euphotic zone. Scolecithricella minor is known to be a detritus feeder, and their reproduction/active growth season was closely associated with high abundance of appendicularians. It implies that discarded 'house' of appendicularians is a major food source for S. minor. As a typical
carnivore, Heterorhabdus tanneri is characterized by intermolt growth of young copepodids being 3 times greater than those of other species, and they achieve a langeorganicmatter deposition during high the abundance season of their potential food (other zooplankton). The vertical distribution of congener species is never overlapped. In the subarctic Pacific, four Metridia spp. and three Paraeuchaeta spp. are predominant. For Metridia species, M pacifica distributed mainly at 0-250 m, M okhotensis at 250-1000 m, M asymmetrica at 1000-2000 m and M curticauda at >2000 m depths. For Paraeuchaeta, P. elongata was at 0-500 m, P. birostrata at 250-1000 m and P. rubra at 500-2000 m depths. Since feeding modes of congener species are similar, vertical partitioning of their habitats within the genus is advantageous to reduce feeding competition between the species. The ontogenetic vertical migration patterns of meso- and bathypelagic copepods are characterized by developmental ascent. In the subarctic Pacific, three Paraeuchaeta species, Gaidius variabilis and Metridia asymmetrica exhibited the ontogenetic vertical migration pattern. Since their lifetime fecundity
is low, starting the early life at depth is advantageous to reduce their predation mortalities. This explanation appears to be consistent with the observation that the fecundity of these copepods decreases with increasing depth. At the same time, developmental ascent is considered to be advantageous to achieve better growth in food-rich upper layers.
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