Protistan algae (phytoplankton) dominate coastal upwelling ecosystems where they form massive blooms that support the world's most important fisheries and constitute an important sink for atmospheric CO₂. Bloom initiation is well understood, but the biotic and abiotic forces that shape short-term dynamics in community composition are still poorly characterized. Here, high-frequency (daily) changes in relative abundance dynamics of the metabolically active protistan community were followed via expressed 18S V4 rRNA genes (RNA) throughout two algal blooms during the spring of 2018 and 2019 in Santa Monica Bay (central Southern California Bight). A diatom bloom formed after wind-driven, nutrient upwelling events in both years, but different taxa dominated each year. Whereas diatoms bloomed following elevated nutrients and declined after depletion each year, a massive dinoflagellate bloom manifested under relatively low inorganic nitrogen conditions following diatom bloom senescence in 2019 but not 2018. Network analysis revealed associations between diatoms and cercozoan putative parasitic taxa and syndinean parasites during 2019 that may have influenced the demise of the diatoms, and the transition to a dinoflagellate-dominated bloom.

中文翻译：

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圣莫尼卡湾（南加州湾中部）春季对比鲜明的藻类大量繁殖的日常动态

_{Protistan 藻类（浮游植物）在沿海上升流生态系统中占主导地位，在那里它们形成大量水华，支持世界上最重要的渔业，并构成大气中 CO 2}的重要汇. 水华的发生已广为人知，但塑造群落组成短期动态的生物和非生物力量的特征仍然很差。在这里，在 2018 年和 2019 年春季圣莫尼卡湾（南加州湾中部）的两次藻华期间，通过表达的 18S V4 rRNA 基因 (RNA) 跟踪代谢活跃的原生生物群落相对丰度动态的高频（每日）变化). 在这两年的风力驱动、养分上升流事件之后形成了硅藻华，但每年都有不同的类群占主导地位。每年硅藻在养分升高后开花，在耗尽后下降，而在 2019 年而非 2018 年硅藻开花衰老后，在相对较低的无机氮条件下出现了大规模的甲藻开花。