Structure of euphausiid assemblages in the Eastern Tropical Pacific off Colombia during El Niño, La Niña and Neutral conditions

Abstract

In order to understand how the structure and composition of euphausiid assemblages are affected by changes in environmental conditions caused by El Niño and La Niña events in the Colombian Pacific, euphausiids present in zooplankton samples obtained during Estudio Regional del Fenómeno El Niño – Cuenca Pacífica Colombiana (ERFEN-CPC) cruises, in September 2009 (El Niño), October 2011 (La Niña) and September 2012 (Neutral) were analyzed. Fifteen species (5 genera) were identified, of which Euphausia diomedeae was the most abundant during El Niño and Euphausia distinguenda was the most abundant during La Niña and the Neutral condition. In addition, considering all euphausiid species found in this study; under La Niña and Neutral conditions, juveniles were the most abundant phase; while during El Niño, furcilia larvae were the most abundant. During the Neutral condition, the total abundance of euphausiids was significantly higher than during El Niño and La Niña, suggesting that the environmental changes caused by these anomalous conditions would affect abundance due to possible movements of the species towards more favourable conditions. Finally, during El Niño, the euphausiid assemblage was significantly different from the other two conditions, suggesting that the increase in temperature produced by this condition affect the structure and composition of euphausiids assemblage in the Colombian Pacific.