Marine Biology

, Volume 144, Issue 4, pp 713–721 | Cite as

Seasonal changes in abundance and development of Calanus pacificus (Crustacea: Copepoda) in the Oyashio–Kuroshio Mixed Region

  • T. KobariEmail author
  • T. Nagaki
  • K. Takahashi
Research Article


Seasonal changes in abundance and development of Calanus pacificus Brodsky were investigated by analyzing samples of different depth strata (0–150 m and 0–1000 m) collected monthly in the Oyashio–Kuroshio Mixed Region. Copepodite stage 5 (C5) emerged from dormancy and matured in early summer. A new generation appeared in July and developed into C5 during summer to autumn. Some of the summer generation arrested development at C5 and persisted below 150 m depth until the following early summer. Although the remainder matured and reproduced in October, a new generation was not observed at the surface during winter. These results suggest that C. pacificus shows two different life-cycle patterns, i.e. one generation annually, with overwintering C5 in deep waters, and two generations annually, with surface development during autumn to winter. The complex life-cycle patterns may be an adaptation to the highly fluctuating surface environment in the Oyashio–Kuroshio Mixed Region.


Zooplankton Biomass Zooplankton Sample Copepodite Stage Oyashio Water Spring Phytoplankton Bloom 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We are grateful to M.D. Ohman for valuable comments and to G.N. Nishihara for corrections of our English. We thank the captain and crews of R.V. “Takuyo Maru” for help with zooplankton sampling. Thanks are extended to three anonymous referees for valuable comments that improved the manuscript. A part of the present study was supported by grants from the Japan Science Technology Corporation; from the program studies on long-term variation of ocean ecosystem/climate interactions based on the Odate collection of the Ministry of Environment of Japan; and from the deep-sea ecosystem and exploitation program of the Fisheries Agency of Japan.


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Copyright information

© Springer-Verlag 2003

Authors and Affiliations

  1. 1.Aquatic Resource Science Laboratory, Faculty of FisheriesKagoshima UniversityKagoshimaJapan
  2. 2.Miyagi Prefecture Fisheries Research and Development CenterIshinomakiJapan
  3. 3.Biological Oceanography Section, Mixed Water Region Fisheries Oceanography DivisionTohoku National Fisheries Research InstituteShiogamaJapan

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