Hae Jin Jeong^1,*, Hee Chang Kang^1,*, An Suk Lim², Se Hyeon Jang¹, Kitack Lee³, Sung Yeon Lee¹, Jin Hee Ok¹, Ji Hyun You¹, Ji Hye Kim¹, Kyung Ha Lee¹, Sang Ah Park¹, Se Hee Eom¹, Yeong Du Yoo⁴ and Kwang Young Kim⁵

¹School of Earth and Environmental Sciences, Seoul National University, Seoul 08826, Korea.
²Division of Life Science and Plant Molecular Biology and Biotechnology Research Center, Gyeongsang National University, Jinju 52828, Korea.
³Division of Environmental Science and Engineering, Pohang University of Science and Technology, Pohang 37673, Korea.
⁴Faculty of Marine Applied Biosciences, Kunsan National University, Gunsan 54150, Korea.
⁵Department of Oceanography, Chonnam National University, Gwangju, Korea.

^*Corresponding author. 

Microalgae fuel food webs and biogeochemical cycles of key elements in the ocean. What determines microalgal dominance in the ocean is a long-standing question. Red tide distribution data (spanning 1990 to 2019) show that mixotrophic dinoflagellates, capable of photosynthesis and predation together, were responsible for ~40% of the species forming red tides globally. Counterintuitively, the species with low or moderate growth rates but diverse prey including diatoms caused red tides globally. The ability of these dinoflagellates to trade off growth for prey diversity is another genetic factor critical to formation of red tides across diverse ocean conditions. This finding has profound implications for explaining the global dominance of particular microalgae, their key eco-evolutionary strategy, and prediction of harmful red tide outbreaks.