Seasonal changes in the planktonic food web off Cape Esan, southwestern Hokkaido, Japan

Abstract

The planktonic food web structure in the water off Cape Esan, southwestern Hokkaido, Japan was investigated at approximately one or two-month intervals from May 1997 through June 1999, based on biomass data of pico-(0.2-2 μm), nano- (2-10 μm), micro- (10-200 μm) and mesoplankton (200-20,000 μm). In spring (March-April), the water column was stratified and a spring diatom bloom occurred. In addition, microzooplankton and copepod biomass was high among the heterotrophic plankton in spring. In other seasons (summer, fall and winter), pico- and nanoplankton assemblages were dominant within the plankton community. These results indicate that the grazing food chain (micro-size phytoplankton - copepods) might be important and the indirect route (micro-size phytoplankton - microzooplankton - copepods) probably prevails in spring, while the microbial food web might be the predominant carbon flow route in other seasons. © The Plankton Society of Japan.