Response to El Niño signals of the epiplanktonic copepod populations in the eastern tropical Pacific

Interannual variability in composition and abundance of the surface copepod populations in the eastern equatorial Pacific was examined in relation to environmental properties (sea surface temperature, salinity, chlorophyll content, and vertical thermal structure) between 1979 and 1984. This period is characterized by the 1982–1983 El Niño‐Southern Oscillation (ENSO) episode, inferring eastward propagation along the equator of several climatic and oceanographic parameters following two phases which have been distinctly observed in the eastern Pacific. During the first phase, November 1982, the thermocline deepening induces a strong drop in primary production and consequently a decrease in abundance of the total copepods in the equatorial area until the end of 1984. During the second phase (second quarter of 1983), a new areal distribution of copepod populations occurs, connected to the southwestward extension of the low‐salinity surface waters from the Gulf of Panama. During the whole ENSO event, the seasonal signal is missing.