Mesoscale variability in the habitat of the Humboldt Current krill, spring 2007

Mesoscale eddies are prominent structures in the world's oceans generating a high degree of spatial and temporal heterogeneity that influences zooplankton distribution. Euphausiids (krill) are a key zooplankton group mainly inhabiting coastal upwelling areas where high productivity, advection, and eddy kinetic energy (EKE) play pivotal roles in the distribution and structure of zooplankton. We analyzed the spatial distribution of the Humboldt Current krill, Euphausia mucronata, in relation to environmental variability and mesoscale circulation during the 2007 austral spring. Using net-based zooplankton samples, remotely sensed environmental conditions, multivariate analysis, and generalized additive models, we described and tested the effect of oceanographic variability and mesoscale eddies on E. mucronata abundance and biomass. E. mucronata was significantly more abundant in coastal (97%) than oceanic habitats, and more abundant in cyclonic cores (mean: 76 indiv. m^-2) than in surrounding waters (mean: 13-29 indiv. m^-2). Abundance correlated to current and EKE fields at >10-20 cm s^-1 and >50-200 cm² s^-2, respectively, and biomass correlated negatively to sea level anomaly and positively to alongshore winds. Krill abundance and biomass were also strongly coupled to both eddy dynamics and the coastal upwelling regime in spring 2007. Mesoscale eddies may doubly influence the E. mucronata population dynamic by retaining krill within them and, by advection from coastal to oligotrophic regions.