Ongoing ocean deoxygenation is threatening marine organisms globally. In eastern boundary upwelling systems, planktonic copepods dominate the epipelagic zooplankton, being crucial in the marine food web. Yet, they must cope with severe hypoxia caused by shoaling of the oxygen minimum zone. Based on laboratory experiments during 2021, we found differential responses in the metabolic rate (MR) and critical oxygen partial pressure of three abundant copepods. Calanoides patagoniensis doubled its MR during the upwelling season, so better exploiting the spring phytoplankton bloom for feeding and reproduction while maintaining their critical oxygen partial pressure unchanged between seasons. Contrastingly, Paracalanus cf. indicus and Acartia tonsa, maintained their MRs throughout seasons, but significantly increased their critical oxygen partial pressure during the upwelling period, becoming less tolerant to hypoxia. Field observations showed that oxygen levels equal to or lower than the critical oxygen partial pressure is a common condition (70% of occurrence) that copepods encounter during the year in the upper 50 m layer. These findings suggest a species‐dependent trade‐off between the MR and the critical oxygen partial pressure, where some species can maintain the latter despite fluctuations in their MR (improved hypoxia tolerance) or maintain their MR at the expenses of a larger critical oxygen partial pressure (improved energy expenditures). These adaptive responses, under oxygen levels equal to or lower than the critical oxygen partial pressure, suggest that exacerbated hypoxia, driven by ocean deoxygenation and increased upwelling, will alter copepod distribution and cause higher copepod mortality, with potentially drastic consequences for marine food webs.

中文翻译：

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在高产沿海上升流区缺氧加剧的情况下调整浮游桡足类的代谢率和临界氧张力

持续的海洋脱氧正在威胁全球海洋生物。在东部边界上升流系统中，浮游桡足类在表层浮游动物中占主导地位，在海洋食物网中至关重要。然而，它们必须应对因最低氧气区浅滩而引起的严重缺氧。根据 2021 年的实验室实验，我们发现三种丰富的桡足类动物的代谢率 (MR) 和临界氧分压存在差异反应。巴塔哥尼亚卡拉诺贝斯在上升流季节，其 MR 增加了一倍，因此可以更好地利用春季浮游植物的繁殖进行摄食和繁殖，同时保持其临界氧分压在季节之间保持不变。相比之下，副卡拉努斯参见野猪和通桑紫杉，在整个季节中保持了它们的 MR，但在上升流期间显着增加了它们的临界氧分压，对缺氧的耐受性变得较差。现场观察表明，氧气水平等于或低于临界氧分压是桡足类在一年中50 m上层遇到的常见情况（70%发生）。这些发现表明，MR 和临界氧分压之间存在物种依赖性的权衡，其中一些物种尽管 MR 波动（改善缺氧耐受性），但仍可以维持后者，或者以更大的临界氧分压为代价来维持 MR压力（改善能量消耗）。在氧气水平等于或低于临界氧分压的情况下，这些适应性反应表明，由海洋脱氧和上升流增加驱动的缺氧加剧，将改变桡足类分布并导致更高的桡足类死亡率，对海洋食物网可能产生严重后果。