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

Abstract

Seasonal 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.

Seasonal variations in abundance and diversity of copepods in Mond River estuary, Bushehr, Persian Gulf

“…It can directly or indirectly impact the distribution of zooplankton, including copepod (Nakata et al 2004;Bigler et al 2006;Pipan et al 2006). The results showed that there was a positive correlation between diversity (0.01> P) and density (0.05> P) of copepods with temperature which is corresponded with increasing the density of copepods in summer and decreasing of them in winter.…”

Observations of vertical turbulent nitrate flux across the Kuroshio

“…Nutrient supply to the surface after the spring stratification due to the turbulent mixing could lead to the high concentration of phytoplankton around the Kuroshio front, which would have an effect on the abundance of zooplankton (e.g., through effects on egg production as suggested by Nakata et al . []) and fishes, in particular larvae, which feed on zooplankton as reported previously [ Nakata et al ., ; Okazaki et al ., , ]. This may be one reason why the Kuroshio is an important nursery ground for many pelagic fishes.…”

Latitudinal distribution of mesozooplankton in the off-equatorial northeastern Pacific before and after the 1998/99 La Niña event

“…The smaller-bodied taxa such as clausocalanids appear to be less influenced by either warm or cold events (Hopcroft et al, 2002). However, Oncaea sp., which was abundant in surface waters during the strong upwelling event in 1999, showed higher abundance concomitant with increased primary production and lowered temperature (Nakata et al, 2004), like omnivores in field observations (Paffenhö fer, 1993). Doubling of the abundance of Oncaea spp.…”