Spatial variability in zooplankton biomass in the lee of the Hawaiian Islands
Sources of food for upper trophic levels of marine communities in the oligotrophic gyre of the subtropical Pacific Ocean are limited to patches of high productivity instigated by physical and topographic features. Ephemeral physical features such as wind-driven cyclonic eddies and fronts generate upwelling nutrients and concentrate food sources, leading to a cascade of productivity that may support large nektonic organisms. I hypothesize that zooplankton are concentrated within eddies by upwelling currents and behavioral preference for food patches. More specifically, I hypothesize nutrient enhancement increases phytoplankton availability and allowing zooplankton to grow and reproduce. Therefore, zooplankton biomass will be higher within the periphery of eddies than in surrounding waters. The Hawaiian Islands are located in the path of the Northeasterly Trade winds, which cause a region of high eddy kinetic energy in the lee of the Islands. Satellite altimetry (SSH), sea surface temperature (SST), and ocean color data will narrow a range of locations with high eddy potential and track eddy development leading up to the cruise. Temperature and fluorescence data collected underway will be used to define the eddy’s perimeter, and the center will be estimated geometrically. Zooplankton tows will be conducted at night at 7 points linearly positioned across two eddy transects. Zooplankton abundance and life stages will be compared with diatom abundance, fluorescence, and temperature to infer the temporal and spatial effects of ocean physical processes on ecosystems in oligotrophic environments. Examination of the relationship between eddies and zooplankton may provide clues to the role of eddies in marine ecosystems.