Journal of Plankton Research Vol.22 no.1 pp.29-46, 2000
© Oxford University Press 2000
Vertical distribution, life cycle and body allometry of two oceanic calanoid copepods (Pleuromamma scutullata and Heterorhabdus tanneri) in the Oyashio region, western North Pacific Ocean
Biological Oceanography Laboratory, Faculty of Fisheries, Hokkaido University, 3-1-1, Minato-cho, Hakodate, Hokkaido 041-0821, Japan 1 Present address: Environmental Chemistry Department Ocean Environmental Survey Team, Kansai Environmental Engineering Center Co., Ltd., 1-3-5, Azuchimachi, Chuo-ku, Osaka 541-0052, Japan
Diel and seasonal vertical distribution, life cycle and body allometry of Pleuromamma scutullata and Heterorhabdus tanneri were investigated in the Oyashio region during September 1996 through October 1997. Monthly samples were collected with 0.1 mm mesh closing nets towed through five discrete depths between the surface and
2000 m. Copepodite stages 1 through 6 of P.scutullata and 3 through 6 of H.tanneri were collected effectively with the nets. Daynight samplings during December 1996, April and October 1997 revealed both species ascend at night. Seasonal differences in the vertical distribution patterns of both copepods were insignificant, and P.scutullata was distributed at a much shallower depth (250500 m) than H.tanneri (600850 m). By tracing the sequential changes in abundance peaks of each copepodite stage, both species are considered to produce one generation per year. The main reproduction season was estimated to occur in spring for P.scutullata and in winter for H.tanneri. The relationships between prosome length and wet weight, dry weight, and ash-free dry weight indicated that the increase in weight per molt was much greater in H.tanneri than in P.scutullata. These dissimilar features are discussed in relation to the dissimilar food habits of these two species and the production cycle of food organisms in the Oyashio region.
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