Large contribution of small phytoplankton at Marian Cove, King George Island, Antarctica, based on long-term monitoring from 1996 to 2008

摘要

To detect and monitor coastal marine ecosystem responses to current environmental changes, the phytoplankton assemblage, salinity, and macro-nutrients were monitored daily at a fixed coastal site in Marian Cove, Antarctica, from 1996 to 2008. The monthly average water temperature at the site was highest (2.14 ± 0.36 ℃) during the summer period (December-February) and lowest (-1.80 ± 0.22 ℃) during the winter period (July-September). The salinity levels exhibited the opposite trend with the lowest values (30.9 ± 0.68 psu) during summer and the highest values (35.2 ± 1.15 psu) during winter. The concentrations of major nutrients were always high enough for phytoplankton growth, indicating the nutrients are not a main controlling factor for phytoplankton growth. Total chlorophyll-a generally started to increase from late November with a peak (1.14 ± 1.41 mg chl-a m~(-3)) around January when the water temperature was the wannest during the year. Within the phytoplankton communities, the average contribution of small (nano- plus pico-) phytoplankton (＜20 μm) to the total chl-a concentration was high (62.9 %) throughout the study period, which supports the observation that small phytoplankton contributed 85.7 % to the cell numbers and 56.4 % to the biovolume of the total phytoplankton. The high contribution of small phytoplankton is a general characteristic at Marian Cove and may be expected to increase under future warming conditions.