Assessment of frontal gradients in zooplankton communities across a coastal upwelling filament by an autonomous Zooglider

In August 2019 we quantified abrupt changes in zooplankton communities across a coastal upwelling filament as part of a Lagrangian study of cross-shore transport and its biogeochemical consequences. This was a component of the multi-disciplinary CCE-LTER (California Current Ecosystem Long-Term Ecological Research) program. While shipboard sampling and experiments were conducted in a coastal filament followed sequentially over time, we simultaneously deployed an autonomous Zooglider for 14 days to characterize cross-filament frontal gradients in the composition and vertical distribution of meso-zooplankton. Zooplankton characteristics were assessed optically by Zoocam, a shadowgraph imaging system that senses zooplankton and marine snow > 0.45 mm equivalent circular diameter, and by Zonar, a dual-frequency (200/1000 kHz) custom built echosounder. Chlorophyll-a fluorescence and pumped CTD measurements were made concurrently. Zooglider was deployed at sea from the R/V Atlantis, then navigated remotely in an adaptive manner to sample across the coastal filament. Crossings of this coastal filament permitted us to resolve pronounced changes in the abundance, biomass, and community composition of meso-zooplankton and marine snow, at high vertical resolution. Our results will demonstrate the advantages of autonomous sampling that is integrated with shipboard measurements, to quantify the ecological and biogeochemical effects of cross-shore fluxes.