Species composition and biogeography of diatoms in Antarctic and Subantarctic (Argentine shelf) waters (37-76ºS)

OLGUIN HF; ALDER VA

DEEP-SEA RESEARCH PART II-TOPICAL STUDIES IN OCEANOGRAPHY

PERGAMON-ELSEVIER SCIENCE LTD

Lugar: Amsterdam; Año: 2010

0967-0645

A large spatial scale study of the diatom species inhabiting from subantarctic (Argentine shelf) to Antarctic waters was made for first time in order to understand relationships between these two regions with regard to the fluctuations of diatom abundances in relation with environmental features, their floristic associations and the effect of the Polar Front as a biogeographic barrier. Species-specific diatom abundance, nutrient and chlorophyll-a concentration were assessed from 64 sub-surface oceanographic stations carried out during austral summer 2002, a period characterized by an anomalous sea ice coverage in correspondence with a “warm year”. Significant relationships of both diatom density and biomass with chlorophyll-a (positive) and water temperature (negative) were found for the study area as a whole. Within the Subantarctic region, diatom density and biomass values were more uniform and significantly (in average: 35 and 11 times) lower than those of the Antarctic region, and did not correlate with chlorophyll-a. In Antarctic waters, instead, biomass was directly related with chlorophyll-a, thus confirming the important contribution of diatoms to the Antarctic phytoplanktonic stock. A total of 167 taxa were recorded for the entire study area, with Chaetoceros and Thalassiosira being the genera best represented. Species richness was maximum in subantarctic waters (46; Argentine shelf) and minimum in the Antarctic region (21; Antarctic Peninsula), and showed a significant decrease with latitude. Floristic associations were examined both qualitatively (Jaccard Index) and quantitatively (Correlation) by cluster analyses and results allowed differentiating a similar number of associations (12 vs. 13, respectively) and two main groups of stations. In the Drake Passage, the former revealed that the main floristic change was found at the Polar Front, while the latter, reflected the Southern ACC Front as a main boundary, and yielded a higher number of isolated sites, most of them located next to different Antarctic islands. Such differences are attributed to the high relative density of F. kerguelensis in Argentine shelf and Drake Passage waters and of Porosira glacialis and species of Chaetoceros and Thalasiosira in the Weddell Sea and in the nearby of Antarctic Peninsula. From a total of 84 taxa recorded in Antarctic waters, only 17 were found exclusively in this region, and the great majority (67) was also present in subantarctic waters but in extremely low (< 1 cell l-1) concentrations probably as a result of expatriation processes via the ACC-Malvinas Current system. The present results were confronted with those of previous studies on the Antarctic region in respect of both diatom associations in regular vs. atypically warm years, and the distribution and abundance of some selected planktonic species reported for surface sediments.