Harmful algal blooms caused by toxin‐producing species of the diatom genus Pseudo‐nitzschia have been linked to anomalously warm ocean conditions in the Northern California Current System. This study compares summertime concentrations of Pseudo‐nitzschia spp. and the toxin they produce, domoic acid, during a marine heatwave year (2019) and a climatologically neutral year (2021). An Imaging FlowCytobot was installed on a fishery survey vessel alongside environmental sensors to continuously sample phytoplankton and oceanographic parameters. This was paired with targeted manual sample collections for nutrients, chlorophyll, and domoic acid. Accumulations of Pseudo‐nitzschia spp. were associated with upwelling zones and established hotspot regions: the Juan de Fuca Eddy, Heceta Bank, and Trinidad Head. Overall, however, Pseudo‐nitzschia spp. and domoic acid concentrations were low during both summers and appear to have been limited by nitrate. Nutrient availability may therefore modulate the response of Pseudo‐nitzschia spp. to warm anomalies. Comparison of these results with 2015, another marine heatwave year but one that produced record concentrations of Pseudo‐nitzschia spp. and domoic acid, suggests that the timing of marine heatwave conditions in the nearshore relative to seasonal upwelling plays a key role in determining whether a Pseudo‐nitzschia spp. harmful algal bloom will occur.

中文翻译：

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营养限制抑制了上升流系统中有害藻类对海洋热浪的反应


由硅藻属拟菱形藻产生毒素的物种引起的有害藻华与北加州洋流系统异常温暖的海洋条件有关。本研究比较了拟菱形藻属的夏季浓度。以及它们在海洋热浪年（2019 年）和气候中性年（2021 年）产生的毒素软骨藻酸。渔业调查船上安装了成像 FlowCytobot 和环境传感器，以连续采样浮游植物和海洋学参数。这与营养物、叶绿素和软骨藻酸的有针对性的手动样品采集相结合。假菱形藻的积累。与上升流区和已建立的热点区域相关：胡安德富卡涡流、赫塞塔浅滩和特立尼达角。然而，总的来说，伪菱形藻属。软骨藻酸浓度在这两个夏季都很低，并且似乎受到硝酸盐的限制。因此，营养物质的可用性可能会调节拟菱形藻的反应。温暖异常。将这些结果与 2015 年进行比较，2015 年是又一个海洋热浪年，但产生了创纪录的拟菱形藻属浓度。和软骨藻酸，表明近岸海洋热浪条件相对于季节性上升流的时间在确定拟菱形藻属是否存在中起着关键作用。将会发生有害的藻华。