2023-08-29 カリフォルニア大学サンディエゴ校(UCSD)
◆カリフォルニア大学サンディエゴ校の研究チームは、このプランクトンの遊泳能力が密な増殖を引き起こす原因であることを明らかにしました。その垂直遊泳能力が、他のプランクトン種に対する競争優位性を生むと指摘され、コケシムシが日中に上昇して光合成を行い、夜間には深い栄養プールにアクセスする行動が生物発光の現象と結びついていることが示されました。
<関連情報>
- https://today.ucsd.edu/story/historic-red-tide-event-of-2020-fueled-by-plankton-super-swimmers
- https://www.pnas.org/doi/10.1073/pnas.2304590120
渦鞭毛藻の垂直移動が強烈な赤潮を引き起こす Dinoflagellate vertical migration fuels an intense red tide
Bofu Zheng, Andrew J. Lucas, Peter J. S. Franks, Tamara L. Schlosser, Clarissa R. Anderson, Uwe Send, Kristen Davis, Andrew D. Barton, and Heidi M. Sosik
Proceedings of the National Academy of Sciences Published:August 28, 2023
DOI:https://doi.org/10.1073/pnas.2304590120
Significance
Extremely dense harmful algal blooms (HABs) are an increasing problem globally. How microscopic, single-celled organisms can reach such high abundances is still poorly understood. Over 50 y ago, it was postulated that motile dinoflagellates could form dense blooms through their vertical swimming, which gave them a competitive advantage over other phytoplankton. We tested this hypothesis with innovative in situ observations during a dense bloom. The motile dinoflagellates swam downward at night into the deep nutrient pool, and upward during the day to photosynthesize. Decreases of nutrients in deep waters were proportional to increases in organism abundance, directly linking organism behavioral and metabolic activities. These observations demonstrate that vertical migration is central to the formation of exceptionally dense dinoflagellate HABs.
Abstract
Harmful algal blooms (HABs) are increasing globally, causing economic, human health, and ecosystem harm. In spite of the frequent occurrence of HABs, the mechanisms responsible for their exceptionally high biomass remain imperfectly understood. A 50-y-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 depletion of deep nitrate 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 anomalous biogeochemical conditions compared to 70 y 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.
