Mesozooplankton predator-prey interactions: encounter rates and variable Diel Vertical Migration as detected by Zooglider

Benjamin Michael Whitmore, Scripps Institution of Oceanography, UCSD, La Jolla, CA, United States and Mark D Ohman, Scripps Institution of Oceanography, La Jolla, CA, United States
Predator-prey interactions can act as major structuring forces for planktonic communities. Present zooplankton physical collection methods cannot resolve the fine-scales (<< 1 m) necessary to resolve zooplankton predator-prey interactions. With recent advances in imaging and machine learning technology, it is now possible to determine planktonic predation encounter rates at the scale at which planktonic organisms interact, over extended periods of time. One such advancement is Zooglider, a fully autonomous mesozooplankton sensing glider, outfitted with a low-power shadowgraph imaging camera, dual-frequency Zonar, Chl-a fluorometer, and pumped CTD. Here we report on seven 1-2 week deployments of Zooglider over the San Diego Trough between July 2017 - October 2018. These deployments yielded ~ 2.4 million high-resolution images that permit in situ sizing, local density measurement, and estimation of probability of prey-predator encounter at 5 cm vertical resolution. Some predator and some prey taxa show predictable ontogenetic changes in vertical habitats, including body size-specific Diel Vertical Migration responses. Assessment of the conditional probabilities of predator encounter reveal body size-, depth-, and season-dependent predation risk. Some such responses are consistent with a Trait-based framework.