Effects of La Niña on recruitment and abundance of juveniles and adults of benthic community-structuring species in northern Chile

Abstract

The El Niño Southern Oscillation (ENSO) has been associated with dramatic changes in adult populations of shallow benthic community-structuring species in northern Chile. However, early ontogenetic stages are more likely to be affected by physical processes associated with ENSO (e.g. increased temperature, upwelling), potentially reflected in differences in recruitment intensity. We evaluated recruitment and abundance of juveniles and adults of the major benthic community-structuring groups (kelps, sea urchins, sea stars, crabs and rockfish) during a period affected by La Niña followed by a period of neutral conditions. Recruitment was several times higher during neutral conditions for sea urchins and sea stars. Lower recruitment during La Niña was probably caused by offshore larval transport caused by increased upwelling. Recruitment of crabs tended to be higher during neutral conditions, but this varied among sites. In contrast to invertebrates, kelp abundance seemed to be controlled by post-settlement processes, as reflected by fewer kelp juveniles after La Niña when the abundance of herbivore fishes strongly increased. Our results highlight the importance of evaluating the effects of ENSO at early ontogenetic stages rather than on adult populations, which are less likely to be affected in an upwelling-dominated system.