LAUSR

Knowledge on the mechanisms that drive population dynamics and shape community structure is a key issue in ecology. Using wavelet methods, we analyzed 17-yr of monthly time-series of marine zooplankton (taxonomic composition, total abundance, and biomass) and their relationship with environmental factors (upwelling index and river outflow). The main mode of variation in all series was annual, and exhibited year-to-year variability. The dynamics of zooplankton aggregated properties showed a strong association with upwelling index and river outflow. The annual oscillation of biomass and abundance increased in 2000 corresponding to the highest amplitudes of environmental forcing. Concomitantly, enhanced synchrony was observed among the main taxonomic groups of zooplankton and among copepod species, the most relevant group in terms of occurrence and abundance. The degree of synchrony appeared to be correlated with the upwelling index and, more closely, with the duration of the upwelling events. The amplified seasonality of the environmental variables from 2000 to 2004, combined with a reduction of off-shore exportation by shortening of upwelling events, favored retention in winter, and primary production in summer. These changes modulated community aggregated properties and affected the stability of the zooplankton community through an increase in inter-specific synchrony allowing the community to shift to another state and likely a reorganization of the community size structure.