In the North Pacific Subtropical Gyre, the daily pulse of photosynthetic carbon (C) fixation is closely balanced by losses. This concert of growth and loss is driven by a diverse assemblage of plankton, including the diazotroph Crocosphaera sp. While primary production is relatively well characterized in this ecosystem, the extent of C transfer to secondary producers is poorly constrained. Here, we use automated imaging flow cytometry and population modeling to study the coupling of C production by Crocosphaera and subsequent grazing by nanoplanktonic protists. Crocosphaera cells represent on average 30% of the nanoplankton detected by the Imaging FlowCytoBot in the surface layer of mesoscale eddies during summertime. The size spectra show a maximum in the frequency of Crocosphaera doublet cells just prior to mitotic division at midday, with an average estimated growth rate of 0.8 ± 0.5 d⁻¹. We also identified potential predators by fitting a Lotka–Volterra model to plankton time series observations. Significant predators include the dinoflagellates Protoperidinium and Dinophysis as well as the ciliate Strombidium, which were all imaged with Crocosphaera in food vacuoles. The estimated C demand of the main grazers fluctuated between 25% and 250% of Crocosphaera new production in an anticyclonic eddy where we observed the onset of a Crocosphaera‐driven bloom. Heterotrophic Protoperidinium drove most of the estimated C demand, with grazing rates nearly equivalent to Crocosphaera growth rates (0.6 ± 0.4 d⁻¹ on average), but saturating at high prey concentrations. Our novel results demonstrate tight coupling between specific protistan predators and a diazotrophic prey.

中文翻译：

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Crocosphaera sp。的生与死。太平洋中的：捕食-被捕食的精细尺度动力学

在北太平洋亚热带环流中，光合作用碳（C）固定的日脉与损失紧密平衡。浮游生物的多样化聚集，包括重氮营养菌Crocosphaera sp ，推动了这种生长与损失的一致。尽管在此生态系统中初级生产的特征相对较好，但向次级生产者转移碳的程度受到的约束很有限。在这里，我们使用自动成像流式细胞仪和种群模型来研究Crocosphaera生产的碳与随后纳米浮游生物原生生物放牧的耦合。鳄科在夏季，细胞在中等规模涡流表层中平均代表通过成像FlowCytoBot检测到的纳米浮游生物的30％。尺寸谱显示正好在正午有丝分裂分裂之前，番红花双胞胎细胞的频率最大，平均估计生长速率为0.8±0.5 d ^-1。我们还通过将Lotka–Volterra模型拟合到浮游生物时间序列观测值中，确定了潜在的天敌。显著大鳄包括甲藻Protoperidinium和鳍藻和纤毛虫急游虫，这都与成像Crocosphaera食品空泡。估计主要食草动物的碳需求量在25％至250％之间波动Crocosphaera在反气旋涡流中的新生产，在那里我们观察到了Crocosphaera驱动的水华的爆发。异Protoperidinium驱车大部分估计Ç需求的，具有放牧率几乎等同于Crocosphaera增长率（0.6±0.4 d ^-1平均），但在高浓度的猎物饱和。我们的新结果表明特定的protistan捕食者和重氮营养的猎物之间紧密耦合。