Affiliation: | (1) Graduate School of Fisheries Sciences, Hokkaido University, Minato-cho, Hakodate, Hokkaido 041-8611, Japan;(2) Hokkaido Prefectural Abashiri Fisheries Experiment Station, Masuura, Abashiri, Hokkaido 099-3119, Japan;(3) School of Environmental Science University of Shiga Prefecture, Hassaka-cho, Hikone, Shiga 522-8533, Japan;(4) Ocean Research Institute, The University of Tokyo, Minamidai, Nakano-ku, Tokyo 164-8639, Japan |
Abstract: | The planktonic food web structure in the subarctic coastal water off Usujiri south-western Hokkaido, Japan was investigated from June 1997 to June 1999, based on seasonal biomass data of pico- (<2 µm), nano- (2–10 µm), micro- (10–200 µm) and mesoplankton (>200 µm), and path analysis using the structural equation model (SEM). In spring, microphytoplankton predominated due to diatom bloom, while pico- and nanophytoplankton predominated in the other seasons, except November and December 1997. The seasonal change in size distribution of heterotrophic plankton was almost similar to that of phytoplankton, and mesozooplankton biomass was high in spring. The path analyses suggest that the main channel in the microbial food web could vary according to phytoplankton size composition, indicating not only the classical food chain (microphytoplankton - copepods) but also the indirect route (microphytoplankton - naked dinoflagellates - copepods). |