Reproductive performance of small-sized dominant copepods with a highly variable food resource in the coastal upwelling system off the Chilean Humboldt Current

Small-sized copepods represent a major contribution to the bulk of zooplankton biomass in highly productive coastal upwelling systems, and they are potentially the key link for channelling autotrophic C towards higher trophic levels, mainly via a heterotrophic food web. Here, we show how these small-sized copepods may efficiently exploit both autotrophic and heterotrophic components of the nanoplankton and microplankton size fractions throughout the year in the upwelling zone off Chile. The nutritional value of these food resources, in terms of C, N and lipid content, may vary extensively. However, copepods can successfully adjust their reproductive performance, measured as egg production and hatching success, in order to maintain high growth rates. This apparent flexibility enables copepod populations to sustain high production rates despite a strongly heterogeneous and variable food resource in the coastal upwelling zone. These findings provide further support to the hypothesis that those small-sized omnivorous copepods, not larger-sized, are the major organisms mediating the flux of phytoplankton C towards higher trophic levels in coastal upwelling systems.