ABUNDANCE AND BIOMASS DISTRIBUTION OF MICROBIAL ASSEMBLAGES AT THE SURFACE IN THE OCEANIC PROVINCE OF ANTARCTIC OCEAN (14th Symposium on Polar Biology)

During the JARE-32 (the 32nd Japanese Antarctic Research Expedition) cruise, bacterioplankton, autotrophic and heterotrophic nanoplankton (2-20 μm in length), and microzooplankton (15-250 μm in length) were collected from the surface of the Indian and Australian sectors of Antarctic Ocean. The average abundance of bacterioplankton was 4.56×10^4 cells/ml, and the biomass was 0.25 mg C/m^3. The values of the autotrophic nanoplankton were 0.5×10^3 cells/ml and 2.27 mg C/m^3, respectively. There were 1.02×10^2 cells/ml of heterotrophic nanoplankton in abundance, and its biomass was 0.71 mg C/m^3. About 30% of the biomass of this assemblage was choanoflagellates. Average abundance and biomass of the microzooplankton were 1.62×10^3 inds./l and 3.78 mg C/m^3, respectively. A large portion of the abundance and biomass of microzooplankton was oligotrichs. Protozoans within micro-sized (15-250 μm) category which ingest preys similar to or larger than themselves were found where biomass ratio of nanoplankton to microzooplankton was low (