Structure and abundance of planktonic ciliates from Antarctic oceanic to Subantarctic neritic ecosystems

SANTOFERRARA, L.F; ALDER, V.A.

BUENOS AIRES

Simposio; 4th OPÈN SCIENCE CONFERECE-SCAR; 2010

Scientific Committee on Antarctic Research

Ciliates stand out due to their high contribution to protozooplanktonic biomass and their role in the transfer of nutrients and energy through planktonic food webs. This is the first study on the taxonomic and size structure, density and biomass of the ciliate community which contrasts an oceanic environment under the regime of the Antarctic Circumpolar Current (Drake Passage) with the subantarctic waters of the Argentine Sea. Sub-surface (9 m) seawater samples for microscopic plankton analysis and chlorophyll a quantification were  collected by a centrifugal pump on board the icebreaker Almirante Irizar at 111 oceanographic stations, along three latitudinal transects (63-35°S) performed during austral summer (January-February 2002 and 2003) and autumn (April 2002). Aloricate oligotrichs dominated over loricate oligotrichs, litostomatids and prostomatids. The microplanktonic size fraction represented 57% and 85% of total ciliate density and biomass, respectively, thus prevailing over nanoplanktonic cells. Following the south to north increase of temperature, ciliate density and biomass increased twofold from oceanic to neritic waters, in coincidence with a tenfold increase of chlorophyll a concentration. Fifty percent of total ciliate abundance was represented by local increases (maximum: 20,000 cells L-1 and 25 ìg C L-1) observed in the vicinity of shelf and slope fronts of the Argentine Sea. In contrast, the influence of the Polar Front was reflected in both the drop of nanociliate abundance and the absence of the autotrophic ciliate Myrionecta rubra in antarctic oceanic waters.