Seasonal changes in the reproduction of three oncaeid copepods in the surface layer of the Kuroshio Extension

Abstract

AbstractSeasonal changes in reproduction rates of three dominant oncaeids, Oncaea media, O. venusta f. venella and O. venusta f. –1, and effects of environmental factors on them were examined in the surface layer (0–30 m) in the Kuroshio Extension and adjacent waters off the Pacific coast of central Japan. The biomass of oncaeid copepods peaked in spring, and remained at about 14% of total copepod biomass throughout the year. Monthly mean specific egg production rates of O. media, O. venusta f. –1 and O. venusta f. venella ranged from 0 to 0.038 day−1, from 0.026 to 0.051 day−1 and from 0.022 to 0.049 day−1, respectively, and were relatively higher from winter to spring. Specific egg production rates of both O. media and O. venusta f. venella were positively related to primary production in the euphotic layer. Analysis of temperature effects on reproduction parameters indicated that low temperature was one cause for high specific egg production rates of O. venusta f. –1 in winter, mainly because of an increase in clutch size. Environmental factors thus affect reproduction of the dominant oncaeids in the surface layer of the Kuroshio Extension, and an increase in temperature and decline in primary production would reduce their reproduction.