Spatial and temporal distribution of tintinnids (Protozoa, Ciliata) in relation to frontal systems and the general hydrologic dynamics of the Southern Ocean (SW Atlantic Sector; 50°-64°S, 65°-49°W

ALDER V.A.; THOMPSON, G.A.

Antarctic Ecosystems: Models for wider Ecological Understanding

The Caxton Press, New Zeland

Lugar: Nueva Zelanda; Año: 2000; p. 203 - 213

Distribution patterns of tintinnid species were assessed from the analysis of 77 microplankton samples collected during four different summer surveys in the southwestern Atlantic sector of the Southern Ocean. Further analysis of the results in relation to major local hydrological constraints and temporal fluctuations allowed recognizing five biogeographic zones within the area of the study: Subantarctic Neritic (SNZ), Subantarctic Oceanic (SOZ), Antarctic Oceanic (AOZ), Antarctic Peninsular (APZ) and Polar Frontal (PFZ) zones. Total number of tintinnid species recorded in the whole study site was 35. As compared to the SOZ, the PFZ and the AOZ yielded noticeably higher biomass values(124 and 303 vs. 20 µgC m-3). The SOZ hosted 13 species characterized by low and uniform overall abundances This trend was quite stable interannually (1993, 1994). The AOZ hosted 10 species, only one of which was surely common also in the SOZ. In this zone, within Drake Passage waters, rich patches were observed appearing in a seemingly random manner, within much poorer areas. Total tintinnid abundance increased at the Polar Front or immediately south of it, although maximum values were detected in the partially ice-covered waters of the Weddell-Scotia Confluence (WSC), probably as a response to the combined action of this front and the Marginal Ice Zone. Low tintinnid densities registered also in the WSC and on 55°W are tentatively explained by a deficient supply or type of food, and to macrozooplanktonic grazing pressure. Some tintinnid species proved to be useful as hydrological indicators of summer frontal locations (Codonellopsis pusilla, Cymatocylis convallaria), extent of the Antarctic Circumpolar Current (Cymatocylis antarctica) and transport by warm or cold eddies. Confrontation of biogeographic (this work) and hydrological zonations (historical data) show an agreement with respect to the summer location of the Polar Front. Opposedly, the location and the extension of the Polar Frontal Zone and the Subantarctic Front as reported in literature do not match tintinnid findings, thus suggesting that the latter constraints are more variable and capable of modifying the basic distribution patterns of planktonic organisms. Immigration of foreign species was 3 to 4 times higher in SOZ than in the AOZ. If foreign species are not taken into consideration, biodiversity estimates for antarctic and subantarctic waters proved very similar. which was surely common also in the SOZ. In this zone, within Drake Passage waters, rich patches were observed appearing in a seemingly random manner, within much poorer areas. Total tintinnid abundance increased at the Polar Front or immediately south of it, although maximum values were detected in the partially ice-covered waters of the Weddell-Scotia Confluence (WSC), probably as a response to the combined action of this front and the Marginal Ice Zone. Low tintinnid densities registered also in the WSC and on 55°W are tentatively explained by a deficient supply or type of food, and to macrozooplanktonic grazing pressure. Some tintinnid species proved to be useful as hydrological indicators of summer frontal locations (Codonellopsis pusilla, Cymatocylis convallaria), extent of the Antarctic Circumpolar Current (Cymatocylis antarctica) and transport by warm or cold eddies. Confrontation of biogeographic (this work) and hydrological zonations (historical data) show an agreement with respect to the summer location of the Polar Front. Opposedly, the location and the extension of the Polar Frontal Zone and the Subantarctic Front as reported in literature do not match tintinnid findings, thus suggesting that the latter constraints are more variable and capable of modifying the basic distribution patterns of planktonic organisms. Immigration of foreign species was 3 to 4 times higher in SOZ than in the AOZ. If foreign species are not taken into consideration, biodiversity estimates for antarctic and subantarctic waters proved very similar. which was surely common also in the SOZ. In this zone, within Drake Passage waters, rich patches were observed appearing in a seemingly random manner, within much poorer areas. Total tintinnid abundance increased at the Polar Front or immediately south of it, although maximum values were detected in the partially ice-covered waters of the Weddell-Scotia Confluence (WSC), probably as a response to the combined action of this front and the Marginal Ice Zone. Low tintinnid densities registered also in the WSC and on 55°W are tentatively explained by a deficient supply or type of food, and to macrozooplanktonic grazing pressure. Some tintinnid species proved to be useful as hydrological indicators of summer frontal locations (Codonellopsis pusilla, Cymatocylis convallaria), extent of the Antarctic Circumpolar Current (Cymatocylis antarctica) and transport by warm or cold eddies. Confrontation of biogeographic (this work) and hydrological zonations (historical data) show an agreement with respect to the summer location of the Polar Front. Opposedly, the location and the extension of the Polar Frontal Zone and the Subantarctic Front as reported in literature do not match tintinnid findings, thus suggesting that the latter constraints are more variable and capable of modifying the basic distribution patterns of planktonic organisms. Immigration of foreign species was 3 to 4 times higher in SOZ than in the AOZ. If foreign species are not taken into consideration, biodiversity estimates for antarctic and subantarctic waters proved very similar. which was surely common also in the SOZ. In this zone, within Drake Passage waters, rich patches were observed appearing in a seemingly random manner, within much poorer areas. Total tintinnid abundance increased at the Polar Front or immediately south of it, although maximum values were detected in the partially ice-covered waters of the Weddell-Scotia Confluence (WSC), probably as a response to the combined action of this front and the Marginal Ice Zone. Low tintinnid densities registered also in the WSC and on 55°W are tentatively explained by a deficient supply or type of food, and to macrozooplanktonic grazing pressure. Some tintinnid species proved to be useful as hydrological indicators of summer frontal locations (Codonellopsis pusilla, Cymatocylis convallaria), extent of the Antarctic Circumpolar Current (Cymatocylis antarctica) and transport by warm or cold eddies. Confrontation of biogeographic (this work) and hydrological zonations (historical data) show an agreement with respect to the summer location of the Polar Front. Opposedly, the location and the extension of the Polar Frontal Zone and the Subantarctic Front as reported in literature do not match tintinnid findings, thus suggesting that the latter constraints are more variable and capable of modifying the basic distribution patterns of planktonic organisms. Immigration of foreign species was 3 to 4 times higher in SOZ than in the AOZ. If foreign species are not taken into consideration, biodiversity estimates for antarctic and subantarctic waters proved very similar.