Influence of El Nino Southern Oscillation phenomenon on coastal phytoplankton in a mixohaline ecosystem on the southeastern of South America: Rio de la Plata estuary

The aim of this study was to analyze the density, diversity, biomass and assemblage composition of the phytoplankton in relation to environmental conditions (physical, chemical, hydrological and meteorological variables), measured under the different scenarios caused by the ENSO phenomenon in the period between 2005 and 2012, in six sampling sites in the tidal freshwater zone of the Rio de la Plata estuary, covering almost 100 km of coastline. The results revealed changes in the structure of the phytoplankton, such as a significant reduction of diversity, and decreases in biomass and phytoplankton density, particularly during El Nino phases. Cyanobacteria were more abundant in the neutral periods, Chlorophyceae dominated La Nina phase while Bacyllariophyceae dominated El Nino. However, no complete replacement of species between cycles was observed. The results obtained were highly variable due to the inherent natural variability of the Rio de la Plata, emphasized by the anthropogenic impact in this area. (C) 2015 Elsevier Ltd. All rights reserved.