VARIABILITY AND INTERACTIONS OF PHYTOPLANKTON AND BACTERIOPLANKTON IN THE ANTARCTIC NERITIC AREA

The distributions of phytoplankton biomass and bacterial populations were investigated at 37 stations on the continental shelf of Terre Adelie (Antarctica) during Austral summer 1989. Despite a potentially favourable environment, phytoplankton biomass was relatively low. Surface chlorophyll a values ranged from 1.2 mg m-3 in the coastal area, with a maximum of 2.5 mg m-3 in the vicinity of the penguin rookeries, to only 0.2 mg m-3 70 km offshore. In the Pointe Geologie Archipelago, diatoms larger than 10 mum were predominant and represented more than 80 % of the total biomass. In off shore waters, these large cells represented only 38 % of the total biomass with 59 % of the biomass in the 1 to 10 mum fraction. Total bacterial abundance ranged from 9.4 x 10(9) to 1.0 x 10(11) cells m-3 and heterotrophic bacteria ranged from 1.4 x 10(6) to 7.7 x 10(8) colony forming units m-3. Frequency of dividing cells ranged from 0.8 to 6.6 %. The highest numbers of heterotrophic bacteria were recorded in the immediate vicinity of penguin rookeries and the lowest in offshore waters. Bacterial biomass represents between 2 to 15 % of total microbial biomass in offshore waters and up to 30 % in the coastal area. There was no direct correlation between bacterial and phytoplanktonic standing stocks. This lack of relationship can be explained by considering the differences in scale. It is suggested that in the coastal area where large diatoms are dominant, the bacteria are mainly dependant on organic matter introduced by bird manuring. On the other hand, in offshore waters where the dominant phytoplankton fraction under 10 mum represents a large part of the microbial loop, an indirect relationship between algae and bacteria may be expected.