Growth rates of diatoms from coastal Antarctic waters estimated by in situ dialysis incubation

Growth rates of phytoplankton (cell diameter <200 μm) were examined using dialysis bags incubated in situ at 3 coastal sites around the Antarctic Peninsula during the austral summer of 1994. The phytoplankton community, which was similar for all 3 sites, was dominated by diatoms of the genera Thalassiosira sp., Nitzschia sp., and Chaetoceros sp. The picophytoplankton community (cell diameter <5 μm) did not increase inside the dialysis bags; however, the diatom populations grew at high 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 the maximal predicted growth rates from the cell size of the diatoms for the in situ temperature of 1.5°C. These results indicate that coastal Antarctic phytoplankton can grow at or near, the maximal rates at the low in situ temperatures. The observation that loss rates are similar to population growth rates helps explain the low biomass of coastal Antarctic phytoplankton relative to the high nutrient availability in these waters.