Abstract

Euphausiids are crustaceans with a complex life cycle that play a significant role in the trophic pathways of the highly productive Humboldt Upwelling System. We studied the effect of upwelling and climate variability on the austral spring distribution and abundance of krill life stages using 8 years of physical and biological sampling off northern Chile. During the study period, conditions shifted from negative to positive temperature anomalies and climate indices. Consequently, large interannual variability associated with the El Nino Southern Oscillation and the Pacific Decadal Oscillation was observed in all life stages, with lower abundances during their positive phases. The distribution patterns and the statistical associations with environmental variables show that the effect of upwelling varies ontogenetically. Eggs, nauplii, calyptopis, and furcilia larvae had higher abundances offshore, suggesting they are transported offshore through the Ekman layer. Juveniles and adults avoid advection via their deeper distribution and vertical migrations, and although they were present in the entire study area, abundances were higher to the south associated with lower salinity. This is the first study evaluating the impacts of climate variability on krill life stages and finds a direct effect of these low-frequency oscillations on krill reproduction and abundance in the HUS.