Long-term zooplankton variability in the southern Patagonian shelf, Argentina

Zooplankton can amplify changes resulting from physical forcing associated with climate change at interannual and longer time scales, so multi-year time series data for the pelagic assemblage can provide useful information about climate-ecosystem interactions. Zooplankton biomass and taxonomic composition were analyzed for the region over the southern Patagonian shelf (SPS) for March 1994 to 2012 to describe interannual patterns of variation, determine the spatial consistency and dominant scale of temporal variability, and examine their relation to the regional hydrography. The biomass of selected taxa, including primarily copepods, amphipods, and euphausiids, decreased in 2003 and remained low until 2012. These patterns were associated with a moderate increase in sea surface temperature. Our observations could not establish the causal mechanisms, but the observed biomass decrease might be related to variation in northward current flow over the SPS, which is driven by large-scale climatological forcing and would result in reduced cold-water availability over SPS. Understanding the drivers of interannual variability in zooplankton composition and biomass of this ecosystem is essential for prediction of impacts of climate change on the pelagic ecosystem, including important commercially fished species.