| Summary: | To evaluate short-term changes in planktonic community, we analysed phytoplankton and zooplankton collected by a sediment trap moored at 150 m of St. K2 (47°N, 160°E) in the western subarctic Pacific with precision of two-day interval during 7 June to 1 July 2006. Phytoplankton flux varied from 480 to 372,290 cells m^-2 day^-1, and had a peak in 17-19 June. Phytoplankton community was composed of five diatom species and one silicoflagellate species. From Bray-Curtis cluster analysis, phytoplankton communities were classified into four groups. Zooplankton abundance ranged from 1,137 to 3,385 inds. m^-2 day^-1 and showed two peaks in 13-15 June and 21-23 June. Throughout the study period, large copepod Eucalanus bungii accounted 50-90% of total zooplankton abundance. Gonad maturation of adult females of E. bungii advanced during the study period: immature occurred before 15 June, developed during 19-27 June and newly recruited specimens to adult females were observed after 25 June. As carnivorous zooplankton, chaetognath community was predominated by Sagitta elegans (99.7% of total abundance). Body length of S. elegans ranged 22-39 mm, and the mean body length gradually increased during the study period (0.21 mm per day, r^2=0.72, p<0.01). Gonad maturation was also observed from immature stages in early June to mature stages in late June. As a characteristics of short-term changes in planktonic community, phytoplankton abundance fluctuated (max : min=780), while stable for zooplankton abundance (max : min=3). Species composition also greatly varied for phytoplankton than that in zooplankton. For zooplankton, development of juvenile and gonad maturation of adult were observed for both herbivores and carnivores. Thus, short-term changes during early summer of subarctic Pacific were characterized by phytoplankton succession in the abundance and species composition and rapid zooplankton growth in the development and maturity.
|
|---|