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Wirewalker data collected during the 2020 Southern California red tide

Zheng, Bofu1; Lucas, Andrew J.1; Franks, Peter J. S.1; Schlosser, Tamara1; Anderson, Clarissa1; Send, Uwe1; Davis, Kristen2; Barton, Andrew D.1; Sosik, Heidi M.3

Published Jul 25, 2023 on Dryad. https://doi.org/10.6076/D1SW2S

Data files

Jul 25, 2023 version files 7.58 MB

Abstract

Harmful algal blooms (HABs) are globally increasing economic, health, and ecosystem threats. In spite of the relatively frequent occurrence of HABs, the mechanisms responsible for their initiation and exceptional abundance remain imperfectly understood. A 50-year-old hypothesis posits that dense dinoflagellate blooms derive from motility: swimming upward during the day to photosynthesize and downward at night to access the deep nutrient pool. This allows dinoflagellates to outgrow their nonmotile competitors. We tested this hypothesis using in situ data from an autonomous, ocean-wave-powered vertical profiling system. We showed that the dinoflagellate Lingulodinium polyedra’s vertical migration led to depletion of the deep nitrate pool during a 2020 red tide HAB event. Downward migration began at dusk, with the maximum migration depth determined by local nitrate concentrations. Losses of nitrate at depth were balanced by proportional increases in phytoplankton chlorophyll concentrations and suspended particle load, conclusively linking vertical migration to the access and assimilation of deep nitrate in the ocean environment. Vertical migration during the red tide created distinctly anomalous biogeochemical conditions compared to 70 years of climatological data, demonstrating the capacity of these events to temporarily reshape the coastal ocean’s ecosystem and biogeochemistry. Advances in the understanding of the physiological, behavioral, and metabolic dynamics of HAB-forming organisms from cutting-edge observational techniques will improve our ability to forecast HABs and mitigate their consequences in the future.