Intense blooms of the heterotrophic dinoflagellate, green Noctiluca scintillans, have been reported annually in the Northern Arabian Sea since the early 2000s. Although not known to produce organic toxins, these blooms are still categorized as a harmful due to their association with massive fish mortalities. Recent work has attributed these blooms to the vertical expansion of the oxygen minimum zone, driven by cultural eutrophication from major coastal cities in western India. As diatoms are preferred prey of green Noctiluca scintillans, more frequent blooms of this mixotroph will likely impact the productivity of important fisheries in the region. The present study uses a satellite algorithm to determine the distribution of both diatom and green Noctiluca blooms in the Northeastern Arabian Sea from 2009 to 2016. The results from shipboard microscopy of phytoplankton community composition were used to validate the satellite estimates. The satellite algorithm showed 76% accuracy for detection of green Noctiluca and 92% for diatoms. Shipboard measurements and data from biogeochemical-Argo floats were used to assess the relationship between oxygen concentrations and green Noctiluca blooms in the Northeastern Arabian Sea. Regardless of the presence of a Noctiluca bloom, the dissolved oxygen in the photic zone was always >70% saturated, with an average oxygen saturation >90%. The variability in the relative abundance of diatoms and green Noctiluca is not correlated with changes in oxygen concentration. These findings provide no evidence that cultural eutrophication has contributed to the decadal scale shifts in plankton composition in the Northeastern Arabian Sea oceanic waters. Conversely, the climatic warming of surface waters would have intensified stratification, thereby reducing net nutrient flux to the photic zone and decreasing silicate to nitrate ratios (Si:N); both factors that could increase the competitive advantage of the mixotroph, green Noctiluca, over diatoms. If so, the decadal-scale trajectory of phytoplankton community composition in the Northeastern Arabian Sea may be a harbinger of future climate-driven change in other productive oceanic systems.

自2000年代初以来，每年在阿拉伯海北部每年都报告异养鞭毛藻，绿色夜光藻（Noctiluca scintillans）的猛烈开花。尽管不知道会产生有机毒素，但由于这些花朵与大量鱼类死亡有关，因此仍被归类为有害物质。最近的工作将这些水华归因于印度西部主要沿海城市的文化富营养化所驱动的最低限氧区域的垂直扩展。由于硅藻是绿色夜光闪烁藻的首选猎物，这种混合营养菌的频繁开花可能会影响该地区重要渔业的生产力。本研究使用卫星算法来确定硅藻和绿色夜光藻的分布2009年至2016年期间，海藻在阿拉伯东北海海域盛放。浮游植物群落组成的船载显微镜检查结果用于验证卫星估计。卫星算法显示绿色夜蛾的检测准确度为76 ％，硅藻的准确度为92％。船上的测量结果和来自生物地球化学-阿果浮游生物的数据被用于评估阿拉伯东北海的氧气浓度与绿色夜光藻绽放之间的关系。无论是否有夜光藻开花，在光化区的溶解氧总是> 70％饱和，平均氧饱和度> 90％。硅藻和绿色夜光藻相对丰度的变异性与氧气浓度的变化无关。这些发现没有证据表明文化富营养化促进了东北阿拉伯海大洋浮游生物组成的年代际尺度变化。相反，地表水的气候变暖会加剧分层，从而减少净养分通向光化区的流量，并降低硅酸盐与硝酸盐的比率（Si：N）；这两个因素都可以提高混合营养菌绿色夜光藻比硅藻的竞争优势。如果是这样，东北阿拉伯海浮游植物群落组成的年代际轨迹可能预示着其他生产海洋系统未来气候驱动型变化的预兆。