Seasonal pattern of zooplankton biomass in the Argentinian shelf off Southern Patagonia (45º - 55º S)

Abstract

Zooplankton biomass in the Argentine Sea off Southern Patagonia was measured during thirteen research cruises carried out between 1992 and 1997 and interpreted in the context of the feeding habits of regional fish resources. Samples were collected with a Nackthai sampler (400-500 µm mesh size) towed obliquely through the water column. Wet weights of the size fraction smaller than 5 mm (mostly made up of copepods), amphipods, euphausiids, mysids and chaetognaths were determined separately. Total zooplankton biomass increased from spring to summer or early autumn. The highest values were consistently located in coastal waters between 51° and 52°S and near the shelf-break from 46° to 48°S. In spring most of the biomass of the entire region was built up of copepods. During late summer-early autumn the contribution of the larger groups increased, with amphipods dominating in the coastal area and euphausiids being more abundant in deeper waters. Mysid biomass was significant only in the innermost coastal area in spring and autumn. The occurrence and densities of chaetognaths increased offshore.