Comparing zooplankton community structure and diel vertical migration in the subarctic Northeast Pacific and Atlantic oceans

Zooplankton community structure plays a key role in determining the fate of net primary production and export of organic matter to the deep sea. We compared diel changes in zooplankton (>200 µm) vertical structure in the subarctic NE Pacific and Atlantic oceans during late summer 2018 and spring 2021, respectively, by analyzing biomass size structure and abundance of major taxa in discrete depth intervals between 0-1000 m. Diel vertical migration (DVM) was pronounced at both sites, with most taxa migrating from daytime depths of ~300-500m into the surface 0-100m at night. Total dry weight biomass was 2 to 5-fold higher in the NE Atlantic than the NE Pacific, except for depths >200m at night. Zooplankton biomass during month-long sampling at both sites was relatively unchanged in the NE Pacific and influenced by passage of four storms in the NE Atlantic. Biomass in the NE Pacific was mostly in the larger (>2mm) size fractions due to large, seasonally migrating copepods Neocalanus and Eucalanus spp., and salps, versus in the NE Atlantic in the epipelagic zone where smaller (