GROWTH-RATES OF DIATOMS FROM COASTAL ANTARCTIC WATERS ESTIMATED BY IN-SITU DIALYSIS INCUBATION

Growth rates of phytoplankton (cell diameter <200 mu m) were examined using dialysis bags incubated in situ at 3 coastal sites around the An tarctic Peninsula during the austral summer of 1994. The phytoplankton community, which was similar for all 3 sites, was dominated by diatom s of the genera Thalassiosira sp., Nitzschia sp., and Chaetoceros sp. The picophytoplankton community (cell diameter <5 mu m) did not increa se inside the dialysis bags; however, the diatom populations grew at h igh growth rates (mean +/- SE = 0.39 +/- 0.18 d(-1)). The growth rates of diatoms measured in the natural community were, however, close to 0 (mean +/- SE = -0.05 +/- 0.22 d(-1)), indicative of a close balance between growth and losses (population loss rate: mean +/- SE = 0.45 +/ - 0.43 d(-1)). The highest observed growth rates closely approached th e maximal predicted growth sates from the cell size of the diatoms for the in situ temperature of 1.5 degrees C. These results indicate that coastal Antarctic phytoplankton can grow at or near, the maximal rate s at the low in situ temperatures. The observation that loss rates are similar to population growth rates helps explain the low biomass of c oastal Antarctic phytoplankton relative to the high nutrient availabil ity in these waters.