Picoplankton abundances in two contrasting areas: the Southern Ocean and the Argentine Sea.

ALDER VA., FRANZOSI C.

Curitiba, Brasil

Simposio; IX SCAR Biology Symposium: Evolution and biodiversity in Antarctica; 2005

SCIENTIFIC COMMITTE ON ANTARCTIC RESEARCH

The ecologic role of picoplankton was investigated for the first time in the Argentine Sea in connection with the Southern Ocean. A high resolution spatial sampling (2 or 3 stations per degree of latitude) was performed by means of a centrifugal pump during Summer and Autumn (2002, 2003) in surface (10 m) waters of the Argentine Sea, Drake Passage, Weddell Sea and Bellingshausen Sea. At each station (200 in total), two subsamples were DAPI-stained on board. Cell concentrations and biomass of cyanobacteria, picoeukaryotic algae and heterotrophic bacteria were estimated by counting (epifluorescence microscope) and by biovolume-to-biomass conversions (imaging system) respectively. Average picoplanktonic abundances (6 x 105 cel.ml-1; Mx: 3 x 106 cel.ml-1), heterotrophic components (which decreased in one order of magnitude in relation with a sharp change of bottom depth and the location of the Subantarctic Front, 55-56°S), and phototrophic ones (which contributed with ~ 4% to total picoplankton; range:1 - 2 x 104 cel.ml-1) showed similar fluctuations during the periods investigated. Picoeukaryotic algae reached very low concentrations at 10 m depth, showing slight increments from Summer to Autumn. New and relevant aspects dealing with environmental factors, picoplanktonic components and other microscopic communities will be discussed.