Summer phytoplankton structure and dynamics in an Antarctic lake (Potter Peninsula, South Shetland Islands)

Abstract

The structure and dynamics of the phytoplankton community of a lake from Potter Peninsula (SSSI N° 13, South Shetland Islands) were analyzed during the 1995-1996 summer together with the main limnological features of this system. The surface of the water body was partially covered by ice (60%) at the beginning of the study. Important changes in the abiotic parameters and in the phytoplankton composition were observed during the melting process. Temperature, pH, conductivity and phytoplankton density and biomass increased during the ice-free period. Chlorophyll-a values were typical of oligomesotrophic lakes. SRP (soluble reactive phosphorus) values were always lower than 4 μg/L, while TP (total phosphorus) concentration fluctuated around 16 μg/L. Chlorophyta and Bacillariophyceae were the dominant groups in terms of density, biomass and species richness. Pseudodictyosphaerium jurisii (Hind.) Hind. (Chlorococcal) was the dominant species. A decrease in species equitability and diversity was observed as a consequence of the high density achieved by this species during the end of February. Other planktonic taxa of Chlorophyta were also present in low number. Bacillariophyceae, mainly represented by tychoplanktonic species, showed a small peak just at the final phase of ice thawing. Thus, an increase in species richness and diversity and a decrease in the similarity index (SIMI) applied to consecutives samples were observed during this period.