Abstract
Trichodesmium biovolume and its distributional pattern were investigated in spring in the East China Sea. It showed surface-biased distribution at all stations where it was detected. The maximum biovolume in each water column was 0-4.4×107 μm3L-1, and it was sometimes larger than that of coccoid cyanobacteria (8.9×106-2.0×107 μm3 L-1). Horizontal distribution of Trichodesmium around the boundary between continental shelf water and Kuroshio water showed different patterns between a large-sized fasciculated form and other forms; the former was more abundant on the Kuroshio side and the latter, small-sized fasciculated form or separate filamentous form, more abundant on the continental shelf side, while the abundance of all types varied temporally. Considering that the large fasciculated form may develop from the separate filamentous form or the small fasciculated form, and it may be more efficient for N2-fixation under an aerobic conditions, this contrastive horizontal distribution might reflect an adaptive enlargement process in Trichodesmium colonies accompanied with passive transport from continental shelf water to more oligotrophic Kuroshio waters.
