Phytoplankton blooms in coastal oceans can be beneficial to coastal fisheries production and ecosystem function, but can also cause major environmental problems^1,2—yet detailed characterizations of bloom incidence and distribution are not available worldwide. Here we map daily marine coastal algal blooms between 2003 and 2020 using global satellite observations at 1-km spatial resolution. We found that algal blooms occurred in 126 out of the 153 coastal countries examined. Globally, the spatial extent (+13.2%) and frequency (+59.2%) of blooms increased significantly (P < 0.05) over the study period, whereas blooms weakened in tropical and subtropical areas of the Northern Hemisphere. We documented the relationship between the bloom trends and ocean circulation, and identified the stimulatory effects of recent increases in sea surface temperature. Our compilation of daily mapped coastal phytoplankton blooms provides the basis for global assessments of bloom risks and benefits, and for the formulation or evaluation of management or policy actions.

沿海海洋浮游植物的大量繁殖有利于沿海渔业生产和生态系统功能，但也可能造成重大环境问题^1,2——但全球范围内尚无关于浮游植物大量繁殖发生和分布的详细特征。在这里，我们使用 1 公里空间分辨率的全球卫星观测结果绘制了 2003 年至 2020 年间每日海洋沿海藻华的地图。我们发现，在调查的 153 个沿海国家中，有 126 个国家发生了藻华。在全球范围内，水华的空间范围（+13.2%）和频率（+59.2%）在研究期间显着增加（ P < 0.05），而北半球热带和亚热带地区的水华减弱。我们记录了水华趋势与海洋环流之间的关系，并确定了近期海面温度升高的刺激效应。我们对沿海浮游植物水华的每日地图汇编为水华风险和效益的全球评估以及管理或政策行动的制定或评估提供了基础。