Tropical Pacific-Wide Variability in Vertical Zooplankton and Micronekton Distributions Related to ENSO

Zooplankton and micronekton are key links in tropical Pacific food webs, which include tuna as top-level predators. Zooplankton and micronekton vertically migrate to deeper depths to avoid visual predators, including tuna, during the day and then return to shallower depths to feed at night. Vertical migration depths vary spatially in the tropical Pacific and are correlated with oxygen, light, and temperature. El Niño-Southern Oscillation (ENSO) causes vertical shifts in the thermocline and oxycline. The accessibility of prey during the day should therefore vary interannually depending on the ENSO phase. We use available acoustic doppler current profiler (ADCP) data from cruises within the tropical Pacific between 1990 and 2019, in combination with remotely-sensed ocean color data and in situ profiles of temperature and dissolved oxygen from World Ocean Database, to investigate the timescales and potential drivers of variability in zooplankton and micronekton vertical distributions in this region. Preliminary results suggest that ENSO-associated variations in vertical migration depths differ across the Exclusive Economic Zones (EEZs) of small island nations in the tropical Pacific. These variations are compared to temperature and oxygen-driven tuna vertical habitat variability to assess potential impacts on tuna.