Influence of oceanographic features on the spatial and seasonal patterns of mesozooplankton in the southern Patagonian shelf (Argentina, SW Atlantic)

SABATINI, M.E.; RETA, R; LUTZ, V.A.; SEGURA, V.; M.C. DAPONTE

JOURNAL OF MARINE SYSTEMS

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2016 vol. 157 p. 20 - 38

0924-7963

Surveys conducted during spring, summer and late winter in 2005?2006 over the southern Patagonian shelf have allowed the seasonal distribution of mesozooplankton communities in relation to water masses and circulation to be investigated. In this system, most of the shelf is dominated by a distinct low salinity plume that is related to the runoff from the Magellan Strait (MSW), while the outer shelf is highly influenced by the cold and salty Subantarctic water (SAW) of the boundary Malvinas Current. Separating these two, the Subantarctic Shelf water mass (SASW) extends over the middle shelf. Correspondingly, the structure of the MSW and SAW mesozooplankton communities was found to be clearly different, while the former and the SASW assemblageswere barely separable. This relatively fresh water mass is actually a variant of Subantarctic water that enters into the region from the south and the shelf-break, and hence its mesozooplankton community was not signifi-cantly different fromthat of the SAWwatermass. Dissimilar species abundance, in turn associated with different life histories and population development, was more important than species composition in defining the assem-blages. Total mesozooplankton abundance increased about 2.5-fold from the beginning of spring to late summer,and then decreased at least two orders of magnitude in winter. Across all seasons copepods represented >70?80% of total mesozooplankton over most of the shelf. Copepod species best represented through all seasons, in terms of both relative abundance and occurrence, were Drepanopus forcipatus and Oithona helgolandica. Although sea-sonal differences in abundance were striking, the spatial distribution of mesozooplankton was largely similaracross seasons, with relatively higher concentrations occurring mainly in Grande Bay and surroundings. The well defined spatial patterns of mesozooplankton that appear from our results in conjunction with the southward wide extension of the shelf and the predicted current path and speed suggest that plankton production is locally enhanced in the Grande Bay area and has the potential to be exported downstream.