Distribución y abundancia del microzooplancton en aguas superficiales del Atlántico Sudoccidental (Campaña TABIA II)

THOMPSON GUSTAVO; ULIANA ELEONORA; BOLTOVSKOY DEMETRIO; BRANDINI, FREDERICO

La Paz, Baja California, México

Congreso; XI Simposium Internacional de Biología Marina; 1996

CICESE

Absolute abundances of foraminifers, polycystine and phaeodarian radiolarians, tintinnids, pteropods, and early crustacean larvae and moults were assessed in a collection of 57 vertically stratified (0-100 m) net microplankton samples from 22 stations located between 34 and 58°S (along 51-56°W), covered in November 9-16, 1994. Tintinnids were identified to species and measured in order to estimate their biomass from biovolume to carbon conversions. Distribution of the microzooplanktonic groups assessed was irregular and patchy, both geographically and vertically, and their abundances are characteristic of oceanic low to medium productivity environments. Tintinnid biomass was also generally low (0.05 to 0.40 µg C l-1). With the exception of the tintinnids, associations between microzooplanktonic numbers and chlorophyll a were generally loose. Eighty-eight tintinnid taxa were recorded, yet only 5 accounted for 53% of the specimens identified. Multivariate (cluster) analysis of tintinnid specific distribution patterns clearly showed several distinct zones, from north to south these are: Transition Zone (TZ), with 3 subzones, TZ north (34°S-38°S), TZ central (39°44’S-44°S), and TZ south (46°S); Subantarctic Zone (SZ, 48-55’S); Polar Front Zone (55°30’S); and Antarctic Zone (AZ, 58-59°36’S). Each of these was characterized by distinct tintinnid composition, abundance and biomass. With few exceptions, tintinnid cells were fairly evenly distributed throughout the upper 50 m. Specific composition usually changed little with depth. Mean population depths were calculated for a subset of 35 tintinnids; 29 of these dwell preferably above 40 m. Spatial distribution of tintinnid species richness showed a more or less gradual decrease from north to south. Specific diversity and equitability generally increased with depth, and were higher in antarctic waters than the southern transitional and subantarctic ones; this trend is tentatively attributed to higher water-column vertical stability south of the Polar Front.