PHYSIOLOGICAL-RESPONSES OF A SMALL ANTARCTIC DIATOM (CHAETOCEROS SP) TO SIMULATED ENVIRONMENTAL CONSTRAINTS ASSOCIATED WITH SEA-ICE FORMATION

The phvsiological responses of a small unicellular Chaetoceros species, isolated from the Weddell Sea, Antarctica, to changes in temperature, Salinity and irradiance simulating those that occur during new-ice formation were investigated. The combination of increased salinity, increased quantum irradiance and decreased temperature significantly reduced growth and photosynthetic rates compared to the control, although cellular metabolism was not inhibited. The cells retained the capacity to photoacclimate, which was observed in the variations in cellular chlorophyll a concentrations and carbon allocation patterns. In terms of photosynthesis, a doubling of quantum irradiance apparently compensated for the adverse effects of increased salinity and lowered temperature. It is thus hypothesized that at least some species of the late season phytoplankton population survive incorporation into ice and continue to photosynthesize and grow under the extreme conditions encountered during sea-ice formation. This potentially prolonges the Antarctic vegetation period well into late austral autumn and winter, enhancing the total primary production available for higher trophic levels.