Dinoflagellate vertical migration fuels an intense red tide
By Dr. Bofu Zheng
Postdoctoral Investigator
Biology Department
Woods Hole Oceanographic Institution 
 
Date:    20 March 2025 (Thursday)
Time:    2 pm – 3 pm
Venue:    Room 6591 (Lift 31 – 32)

Abstract:
Harmful algal blooms (HABs) are increasing globally, posing economic, human health, and ecosystem threats. Despite the frequent occurrence of HABs, the mechanisms responsible for their exceptionally high biomass remain imperfectly understood. A 50-year-old hypothesis posits that some dense blooms derive from dinoflagellate motility: organisms swim upward during the day to photosynthesize and downward at night to access deep nutrients. This allows dinoflagellates to outgrow their nonmotile competitors. We tested this hypothesis with in situ data from an autonomous, ocean-wave-powered vertical profiling system. We showed that the dinoflagellate Lingulodinium polyedra’s vertical migration led to the depletion of deep nitrate during a 2020 red tide HAB event off Southern California. 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. The application of cutting-edge observational techniques, including high-resolution autonomous sensors and whole-water-column profiling systems, presents unique opportunities for advancing our understanding of the physiological, behavioral, and metabolic dynamics of HAB-forming organisms, which will improve our ability to forecast HABs and mitigate their consequences in the future. 
 
Biography:
Bofu Zheng is a postdoctoral investigator at the Woods Hole Oceanographic Institution. He is a sea-going oceanographer broadly interested in physical-biological interaction problems, nutrient dynamics, and the development and application of in situ platforms for collecting high-resolution physical and biogeochemical observations. He holds degrees from Zhejiang University (B.E., Mechanical engineering), and Scripps Institution of Oceanography, University of California, San Deigo (M.Sc. and Ph.D., Oceanography).

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