Algal blooms are frequently dominated by motile species1,2 whose vertical migration enhances resource acquisition and bloom development3,4. Yet bloom conditions present a paradox: high cell densities intensify nutrient depletion5 and self-shading6, making individual swimming increasingly costly under severe resource limitation. How motile blooms persist and remain resilient under such stress remains unresolved7, particularly as climate-driven warming strengthens stratification and resource scarcity8,9. Here we show that the red-tide-forming phytoplankton Heterosigma akashiwo overcomes bloom-induced constraints through bioconvection, a self-generated active flow that emerges above a critical cell density (>1.5x105 cells/ml). Using a custom ocean-on-chip platform that recapitulates bloom-relevant constraints, we identify an optimal synergy of cell concentration, swimming speed and gravitactic stability that promotes the formation of persistent bioconvective plumes. At constant cell density, plume onset is governed by two phenotypic traits-- vertical swimming velocity and reorientation time--demonstrating that collective transport is governed by the biophysical traits of single cells. We show that bioconvection drives ecologically relevant multiscale transport, enhancing exchange of molecules and micro-cargo across stratified interfaces, mimicking transport of nutrients, extracellular vesicles10 and co-existing species in a bloom environment11. By enabling cells to hitch a hike on self-generated flows when active propulsion becomes energetically prohibitive, bioconvection-mediated transport improves nutrient delivery, restores photosynthetic performance, reverses lipid accumulation associated with nutrient-stress, and facilitates recovery of cellular motility to ultimately mitigate resource limitations. Our findings identify bioconvection as a population-level adaptive mechanism that sustains algal blooms, and reveal a previously unrecognised role of collective microbial motion in bloom persistence under ecological stresses.
1. 赤潮通常由运动型藻类主导1,2，其垂直迁移行为能增强资源获取并促进赤潮发展3,4。然而赤潮环境存在悖论：高细胞密度会加剧营养耗竭5和自我遮蔽效应6，在资源严重受限时个体游动成本急剧上升。运动型赤潮如何在此类压力下持续存在并保持韧性仍是未解之谜7，尤其当气候变暖强化水体分层和资源稀缺性时8,9。本研究发现，形成赤潮的浮游植物Heterosigma akashiwo通过生物对流突破赤潮引发的限制——这是一种在临界细胞密度（>1.5×10⁵ cells/ml）以上自发形成的主动流动。通过定制模拟赤潮环境限制的海洋芯片平台，我们识别出细胞浓度、游动速度和趋重稳定性的最优协同效应，这种协同促进了持久性生物对流羽流的形成。在恒定细胞密度下，羽流的产生由两个表型特征（垂直游动速度和重定向时间）决定，表明集体运输受单细胞生物物理特性调控。研究证实生物对流驱动具有生态意义的多尺度运输，增强分子和微载体在分层界面间的交换，模拟赤潮环境中营养物质、细胞外囊泡10及共存物种11的运输机制。当主动推进因能量消耗过大而不可持续时，细胞通过搭乘自生成流动实现生物对流介导的运输，从而改善营养输送、恢复光合性能、逆转营养胁迫相关的脂质积累，并促进细胞运动能力恢复，最终缓解资源限制。我们的发现揭示生物对流是维持赤潮的群体适应机制，并首次阐明集体微生物运动在生态压力下对赤潮持续性的关键作用。
One sentence summarySelf-organised bioconvection drives multiscale transport and resilience in algal blooms.
2. 一句话总结：自组织生物对流驱动赤潮中的多尺度运输与韧性维持。
Mishra, S. et al. · CC-BY 4.0