Temporal plankton dynamics in a maritime Antarctic Lake
Changes in abundance, diversity and productivity of plankton in a maritime Antarctic lake were studied between December 1994 and February 1996. There were large intra- and inter-annual fluctuations in population densities, which were related to changing physical and chemical parameters. The plankton included an abundant protozoan population, comprising at least 66 taxa. This is amongst the highest diversities so far reported for Antarctic lakes. Heterotrophic nanoflagellates (HNF) were the most common, with densities between 4 × 104 and 1.5 × 107 l-1, and were the largest contributors to total protozoan carbon biomass for most of the year. Ciliate abundance varied from 4.0 × 100 to 1.4 × 104 l-1 and included taxa from several trophic levels. Numbers of naked amoebae were usually low but occasional patches of high density occurred. An anoxic sump developed in bottom waters at the end of the winter and this contained a distinct population of anaerobic HNF. There was evidence that the excrement of increasing fur seal numbers in the lake catchment over the last 15 years is having an impact on the lake ecosystem. The Chl-a maximum of 49 μg l-1 and primary productivity of up to 40 mgC m-3 h-1 were significantly higher than those reported by previous studies of this lake and continental Antarctic lakes. Increased summer bacterial abundance and productivity, together with higher winter nutrient concentrations, were also noted.