In the relatively unproductive waters of the tropical ocean, islands can enhance phytoplankton biomass and create hotspots of productivity and biodiversity that sustain upper trophic levels, including fish that are crucial to the survival of islands’ inhabitants. This phenomenon, termed the island mass effect 66 years ago, has been widely described. However, most studies focused on individual islands, and very few documented phytoplankton community composition. Consequently, basin-scale impacts on phytoplankton biomass, primary production and biodiversity remain largely unknown. Here we systematically identify enriched waters near islands from satellite chlorophyll concentrations (a proxy for phytoplankton biomass) to analyse the island mass effect for all tropical Pacific islands on a climatological basis. We find enrichments near 99% of islands, impacting 3% of the tropical Pacific Ocean. We quantify local and basin-scale increases in chlorophyll and primary production by contrasting island-enriched waters with nearby waters. We also reveal a significant impact on phytoplankton community structure and biodiversity that is identifiable in anomalies in the ocean colour signal. Our results suggest that, in addition to strong local biogeochemical impacts, islands may have even stronger and farther-reaching ecological impacts.

在热带海洋相对贫瘠的水域中，岛屿可以增加浮游植物的生物量，并创造生产力和生物多样性的热点，以维持上层营养水平，包括对岛屿居民生存至关重要的鱼类。这种现象在 66 年前被称为岛屿质量效应，已被广泛描述。然而，大多数研究都集中在单个岛屿上，很少有记录的浮游植物群落组成。因此，流域规模对浮游植物生物量、初级生产和生物多样性的影响在很大程度上仍然未知。在这里，我们从卫星叶绿素浓度（浮游植物生物量的代表）系统地识别岛屿附近的富集水域，以在气候学基础上分析所有热带太平洋岛屿的岛屿质量效应。我们在 99% 的岛屿附近发现了浓缩物，影响热带太平洋的 3%。我们通过对比富含岛屿的水域和附近的水域来量化叶绿素和初级生产的当地和盆地规模的增加。我们还揭示了对浮游植物群落结构和生物多样性的重大影响，这可以在海洋颜色信号的异常中识别出来。我们的研究结果表明，除了强烈的局部生物地球化学影响外，岛屿可能具有更强和更深远的生态影响。