Changes in oceanographic conditions and zooplankton community structure were investigated during a five year period, which included the 1997-98 El Niño (EN), in the coastal region off Antofagasta (23ºS), northern Chile. We aimed at examining the changes in abundance and size composition of zooplankton, as well as the main oceanographic changes associated with the onset and evolution of the EN.This study was supported by FONDECYT Grant 1000419, 5960002-1996 and PCCI CONICYT/CSIC 2000-2-083.Peer reviewed