Changes in the nekton community structure of the Northern Humboldt Current System under ENSO scenarios

The Northern Humboldt Current System (NHCS) is a highly productive upwelling system that covers the northern-central area of Peru. NHCS is the area where the El Niño Southern Oscillation (ENSO) phases, and climate variability in general, are most noticeable. The ENSO warm phase, or El Niño, reduces dramatically the coastal upwelling due to a stronger stratification of the column water. Conversely, the cold phase, or La Niña, strengthen the coastal upwelling, therefore expanding the area of cold coastal waters. These fluctuations trigger changes in the biological productivity of the ocean as well as in species behavior across different trophic levels (feeding, reproduction, growth, etc.). The main goal of our study is to describe the broad-scale changes in the spatial structure and composition of the nekton community under three ENSO phases: El Niño, La Niña and Neutral. El Niño scenario brings out the highest values of alpha diversity and species richness, and La Niña yields the lowest values. On the other hand, the spatial structure of the community predominantly shows four areal groups (with mostly pelagic, oceanic, northern-warmer, and southern-colder species), which vary in terms of areal extension and species richness across the three scenarios. A redundancy analysis (RDA) of community composition explained by environmental variables describes the relations between some important characteristics (temperature and salinity) of the water masses presents in NHCS and the species composition. Climate change models predict an increase of the frequency of El Niño events, therefore variations in nekton community should be taken into consideration to weaken the impacts on the fishery community.