The impacts of El Niño Southern Oscillation on the pelagic fish community structure of the northern Humboldt Current system

The northern Humboldt Current System (HCS) is a highly productive eastern boundary upwelling system off Peru. El Niño Southern Oscillation (ENSO) is one of the main drivers of short-term climate variability, whose warm (El Niño) and cold (La Niña) phases can trigger changes in the physical, chemical, biological, and socioeconomic conditions of the northern HCS. We explored the impacts of ENSO phases and magnitude in the region over the structure of the pelagic fish community in the northern HCS through the study of spatial and temporal beta diversity changes. To achieve this goal, we used 25-year taxonomic composition data from pelagic scientific surveys and statistical multivariate methods. We found that, depending on the magnitudes, most of the El Niño (EN) categories substantially increased the diversity index values in this system with respect to the neutral phase. In contrast, La Niña (LN) decreased it. The community spatial structure principally showed three ecological regions, which varied in extension, indicator species, and composition across ENSO phases. The local contribution to beta diversity (LCBD) showed that the shelf break is essential in shaping the community structure among ENSO phases. The changes in temporal beta diversity suggest that the spatial structure or change of the community abundance is influenced by the magnitude of the EN phase. We conclude that the oceanographic changes caused by the ENSO phases may significantly impact the fish community structure in the northern HCS. Our results are relevant to implementing climate-ready management measures in this ecosystem.