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