Succession of pelagic copepod species in coastal waters off northern Chile: the influence of the 1997–98 El Niño

Abstract

A 2-year time series (∼ 17-d interval) of zooplankton, sampled from June 1996 through January 1998, along with oceanographic data, allowed the study of species abundances and diversity during non-El Nino and El Nino conditions at Mejillones (23° S) northern Chile. A total of 28 species was identified, of which the most abundant were the calanoids Paracalanus parvus, Calanus chilensis, Acartia tonsa, and Centropages brachiatus, the cyclopoid Oithona similis, and the poecilostomatoids Oncaea conifera and Corycaeus typicus. El Nino Southern Oscillation (El Nino) was first detected in the area in May 1997 and persisted until March 1998. We divided the time series into two parts: non-El Nino conditions. The number of species significantly increased during Eland El Nino conditions, but total abundance of copepods was greater during non-El Nino conditions. Although some expatriate species appeared during El Nino, such as the harpacticoid Microsetella norvegica and Eucalanus subtenuis, the diversity index of Hulburt was not significantly different between the two periods. Despite the dramatic alteration of oceanographic conditions during the El Nino period, we concluded that the community of pelagic copepods was not subject to drastic changes either in total abundance or in structure.