Comparison of the 1982-1983 and 1997-1998 El Nino effects on the shallow-water fish assemblage of the Patos Lagoon estuary (Brazil)

Abstract

Meteorological impacts of El Niño events of 1982–1983 and 1997–1998 were observed in locations throughout the world. In southern Brazil, El Niño events are associated with increased rainfall and higher freshwater discharge into Patos Lagoon, a large coastal lagoon that empties into the Atlantic Ocean. Based on interdecadal meteorological and biological data sets encompassing the two strongest El Niño events of the last 50 yr, we evaluated the hypothesis that El Niño-induced hydrological changes are a major driving force controlling the interannual variation in the structure and dynamics of fishes in the Patos Lagoon estuary. High rainfall in the drainage basin of the lagoon coincided with low salinity in the estuarine area during both El Niño episodes. Total rainfall in the drainage basin was higher (767 versus 711 mm) and near-zero salinity conditions in the estuarine area lasted about 3 mo longer during the 1997–1998 El Niño event compared with the 1982–1983 event. Hydrological changes triggered by both El Niño events had similar relationships to fish species composition and diversity patterns, but the 1997–1998 event appeared to have stronger effects on the species assemblage. Although shifts in species composition were qualitatively similar during the two El Niño events, distance between El Niño and non-El Niño assemblage multivariate centroids was greater during the 1996–2000 sampling period compared with the 1979–1983 period. We provide a conceptual model of the principal mechanisms and processes connecting the atmospheric-oceanographic interactions triggered by the El Niño phenomena and their effect on the estuarine fish assemblage.