Depth distribution, biomass and taxonomic composition of subtropical microbial community in southwestern Japan

We compared the depth distribution, biomass and taxonomic composition of subtropical microbial community among the three stations in the Kuroshio waters around southwestern Japan. While subsurface chlorophyll maximum was evident for all stations, it was not corresponded to depth distributions of carbon-based biomass for phytoplankton and heterotrophic bacteria, nanoplankton and ciliates. The predominant component was diatoms for phytoplankton biomass at all stations, and naked ciliates as St. A and St. C or heterotrophic nanoplankton at St. B for microzooplankton biomass. Although microbial standing stock and size composition were much different among the three stations, biomass of heterotrophic bacteria and respiratory requirement of heterotrophic ciliates and nanoplankton showed a small fluctuations. These results suggest that heterotrophic bacteria are major food resources and pico- to nano-sized phytoplankton are supplement for heterotrophic ciliates and nanoplankton in the Kuroshio waters around southwestern Japan.