El ecosistema de la plataforma patagónica austral, marzo-abril 2000. Composición, abundancia y distribución del zooplancton.

Abstract

The abundance, distribution and structure of the zooplankton community in southern Patagonia (SW Atlantic Ocean) were studied during late summer (March-April 2000) from samples obtained with Nackthai (390 ~km) and Multinet (150 ~km) samplers. Total concentrations of zooplankton biomass, integrated in the water column, ranged between 1.0 and 14.5 g m-2 (dry weight) and reached the highest values in the mid and outer shelf off Bahía Grande (Santa Cruz Prov., Argentina) (51~'S). The < 5 mm size fraction, composed mainly of copepods represented, on average, 45% of the total; amphipods and euphausiids accounted for 20% and 31%, respectively. Amphipods were, almost exclusively, Themisto gaudichaudii and euphausiids most abundant species Euphausia lucens and Thysanoessa gregaria. Drepanopus forcipatus, Calanus australis and Oithona spp. constituted the dominant copepods with high abundance of the first in the whole area that represented, on average, 85% of the total mesozooplankton. The maximum abundances of Drepanopus forcipatus, recorded in outer waters of Bahía Grande, showed a noticeable decrease towards the inner area and to the north of the bay. C. australis and Oithona spp. concentrations, although much lower, distributed more homogeneously within the whole study area. The distribution of the different populations in the water column varied according to the species: D. forcipatus and Oithona spp. concentrated mainly in the upper layers down to ca. 50 m; C. australis was found between that depth and near the bottom. Copepods populations were dominated by late copepodids.