Phytoplankton abundance and community structure in the Antarctic polar frontal region during austral summer of 2009

The Antarctic polar front region in the Southern Ocean is known to be most productive. We studied the phytoplankton community structure in the Indian sector at this frontal location during late austral summer (February, 2009) onboard R/V Akademic Boris Petrov. We used the phytoplankton and microheterotrophs abundance, as also the associated physico-chemical parameters to explain the low phytoplankton abundance in the study region. This study emphasizes the shift of phytoplankton, from large (>10 μm) to small (<10 μm) size. The phytoplankton abundance appears to be controlled by physical parameters and by nutrient concentrations and also by the microheterotrophs (ciliates and dinoflagellates) which exert a strong grazing pressure. This probably reduces small (<10 μm) and large (>10 μm) phytoplankton abundance during the late austral summer. This study highlights the highly productive polar front nevertheless becomes a region of low phytoplankton abundance, due to community shifts towards pico-phytoplankton (<10 μm) during late austral summer.