Journal of Plankton Research Vol.25 no.5 pp.483-494, 2003
© Oxford University Press 2003
Interannual variations in abundance and body size in Neocalanus copepods in the central North Pacific
Aquatic Resource Science Laboratory, Faculty Of Fisheries, Kagoshima University, 4-50-20 Shimoarata, Kagoshima 890-0056, 1 Biodiversity Laboratory, Faculty Of Fisheries, Hokkaido University, 3-1-1 Minato-Machi, Hakodate, Hokkaido 041-8611 and 2 Pelagic Fish And Cephalopod Biology Section, Hokkaido National Fisheries Research Institute, 116 Katsurakoi, Kushiro, Hokkaido 085-0802, Japan
* Corresponding Author: kobari{at}fish.kagoshima-u.ac.jp
As the integral components of zooplankton in the subarctic North Pacific, the three Neocalanus species (N. cristatus, N. plumchrus and N. flemingeri) are characterized by an annual life cycle and rapid development in the surface layer during spring–summer. Patterns of interannual variation of abundance and body size of these Neocalanus species were analyzed using the time-series data collected during the summers of 1979–1998 (20 years) at stations along the longitudinal transect line in the central North Pacific, crossing five sub-areas (Alaska Current System, Subarctic Current System, Northern Transition Domain, Southern Transition Domain and Subtropical Current System). In the southern sub-areas, quasi-decadal oscillation was observed for the 3-year running mean of abundance and prosome length for copepodite stage 5 (C5) of the three Neocalanus species. Although the oscillation signal diminished towards northern waters, it showed a positive phase during the early 1980s and 1990s and a negative phase during the late 1980s. In the northern waters, a biennial pattern was pronounced for anomalies of C5 prosome length for N. plumchrus and N. flemingeri, which was large in odd years and small in even years. Significantly positive covariations among the three species were found for both abundance and prosome length around mid-latitude, where they were abundant. In the correlation analysis, these observed yearly patterns showed a statistically insignificant correlation with most environmental (integrated mean temperature in surface waters, water column stability and chlorophyll a concentration) or climatological (North Pacific Index and Southern Oscillation Index) variables. The regional difference of the oscillation signal and the synchronized covariation among these species suggest that interannual variations of their abundance and body size are mediated by common environmental force(s) with some spatial and temporal scales in the subarctic North Pacific.