Spatial distribution and abundance of diatoms (>20 ƒÝm) and silicoflagellate species in the Southern Ocean and Argentine Sea .

HÉCTOR OLGUÍN SALINAS; VIVIANA A. ALDER

Curitba, Brasil

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

SCIENTIFIC COMMITTE ON ANTARCTIC RESEARCH

Numbers and species of siliceous microphytoplanktonic components from Antarctic Peninsula, Weddell Sea and Argentine Sea (outer shelf: 40-51¢XS, 61-62¢XW) were assessed in relation with environmental factors through a surface (10m) sampling during austral Summer 2002 (60 stations). Species were identified, and their cell densities and biomass values estimated by countings under an inverted microscope and by biovolume-to-carbon conversions, respectively. A principal component analysis based on the abundance of 169 diatom species allowed identifying two main areas: 41-54.5º S and 55-78º S, separated by the Subantarctic Front. The northern sector is characterized by low cell densities (mean: 288 cel.ml-1; mx: 2700 cel.ml-1; biomass: 9 x 10-4 mgC l-1), whereas the southern one hosts highest cell concentrations and biomass (mean: 74 292 cel.ml-1; mx: 777 213 cel.ml-1; biomass: 254 mgC l-1. This pattern is in agreement with the north-to-south increase of silicates and nitrates (5.68 - 34 mM and 1.92 - 11.5 mM, respectively). In terms of mean specific richness and diversity values, the areas are quite similar (40 and 34 species, 3.55 and 3 bits respectively).  Near 20 different diatom associations were found. Silicoflagellates showed a similar trend although with two orders of magnitude below diatoms (mx.: 4000 cel.ml-1, 1.8 mgC l-1 at Weddell Sea).