MICROPHYTOPLANKTON ASSEMBLAGES IN THE WATERS SURROUNDING SOUTH GEORGIA, ANTARCTICA DURING AUSTRAL SUMMER 1994

The composition and distribution of microphytoplankton assemblages in the vicinity of South Georgia were examined during a krill survey cond ucted during voyage 119 the RV Africana in austral summer (January/Feb ruary) 1994. Microphytoplankton distribution was studied at 83 station s along a zig-zag transect in the waters surrounding South Georgia. Oc eanographic and zooplankton data suggest that conditions were anomalou s during the investigation, in that sub-Antarctic surface waters had p robably been advected southwards and were present around the island. T he two most widely distributed species were Corethron criophilum and E ucampia antarctica, which were recorded at all stations sampled. Also well-represented amongst the microphytoplankton assemblages were tempe rate, neritic species such as Chaetoceros atlanticus, Proboscia alata and Odontella weissflogii. This can probably be related to the intrusi on of sub-Antarctic surface waters unusually far south. Cluster and or dination analysis identified three distinct groupings of stations in t he waters surrounding the islands. These were found to the east, west and north of the islands. The diatom groupings identified during this investigation broadly correspond to three water masses previously desc ribed in the vicinity of South Georgia. Despite the anomalous hydrogra phical conditions that existed during the investigation, the differenc es in phytoplankton were negligible when compared to normal years. Sma ll mesoscale features are, however, important in imposing biogeographi c patterns on microphytoplankton.