Zooplankton community in coastal waters of the southern patagonian shelf during early autumn: Diversity and distribution pattern linked to regional water circulation

Abstract

Zooplankton composition, abundance and distribution in the south end of the Argentine continental shelf, although documented on a large scale, is still poorly constrained at higher spatial resolution in many specific areas. This work explores the distribution and composition of zooplankton off the coast of Tierra del Fuego during early autumn, to expand the knowledge about the biological significance of this marine region, located between the Magellan Strait and the Beagle Channel. During an oceanographic survey in early autumn 2014, samples were collected with a 300 μm mesh Bongo net. A total of 20 zooplanktonic groups were recorded and 37 species identified. The Margalef index ranged between 2.24 and 4.18 among sampling stations, with high values in stations 27 and 25, which exhibited the highest diversity of copepods, chaetognaths, mysids, and amphipods. Copepods were the most abundant (730 ind/m³ in average), with Drepanopus forcipatus as the dominant species, followed by mysids, mainly of the species Neomysis monticelli, and the euphausiid species Euphausia lucens and Thysanoessa gregaria. The non-metric multidimensional scaling and hierarchical cluster analysis revealed two distinct geographic sectors, defined by species´s abundance and presence/absence. High zooplankton abundance was observed near the coast at 54°S, where sea surface temperatures were warmer, with a decrease towards deeper and colder waters. Local circulation dynamics inferred from global reanalysis data, including the southward advance of a coastal tongue of warm water during the sampling days and the formation of an anticyclonic vortex, significantly influenced zooplankton distribution in the area.