Temporal and spatial variation of phytoplankton in Admiralty Bay, South Shetlands: the dynamics of summer blooms shown by pigment and light microscopy analysis

摘要

We conducted an integrated study of phytoplankton taxonomic composition, biomass and physicochemical properties of the water in Admiralty Bay, South Shetlands. The aim of the study was to provide detailed information on phytoplankton composition and diversity related to relevant environmental conditions. High-performance liquid chromatography pigment analysis and microscopy were performed in the summers of 2007 and 2009-2010. Results for 2007 showed a typical high-nutrient, low-chlorophyll system. Total carbon biomass and cell numbers were dominated by nanoflagellates, while diatoms made up 1.2-4.5 % of the total algal numbers and contributed a maximum of 23.4 % to the total cell carbon. A small algal bloom occurred in the center of the bay, with chlorophyll a values of similar to 1.0 A mu g l(-1). The prevalent pigment was 19'-hexanoyloxyfucoxanthin, characteristic of the Prymnesiophyceae. In January 2010, the values of chlorophyll a (8-24 A mu g l(-1)) and cell carbon (150 A mu g l(-1)) were the highest ever recorded for Admiralty Bay. In general the algal populations were dominated numerically by nanoflagellates, but a bloom of diatoms (maximum 30 % of total cells and 50 % of total cell carbon) was observed. Diatoms were dominated by those of micro-size: Thalassiosira ritscheri and T. antarctica. The dominant pigment was fucoxanthin, mainly found in diatoms. The diatom bloom could be related to the southeast wind direction, stable water column conditions and an inflow of diatom-rich waters from the Bransfield Strait, while the input of high-turbidity, low-salinity water from melting glaciers and strong katabatic northwest winds could favor nanoflagellates.