Verberk Wilco C E P, Durance Isabelle, Vaughan Ian P, Ormerod Steve J
Department of Animal Ecology and Physiology, Radboud University Nijmegen, Heyendaalseweg, 135, 6525 AJ, Nijmegen, The Netherlands.
Catchment Research Group, Cardiff School of Biosciences, Cardiff University, Cardiff, CF10 3AX, UK.
Glob Chang Biol. 2016 May;22(5):1769-78. doi: 10.1111/gcb.13240. Epub 2016 Feb 29.
Aquatic ecological responses to climatic warming are complicated by interactions between thermal effects and other environmental stressors such as organic pollution and hypoxia. Laboratory experiments have demonstrated how oxygen limitation can set heat tolerance for some aquatic ectotherms, but only at unrealistic lethal temperatures and without field data to assess whether oxygen shortages might also underlie sublethal warming effects. Here, we test whether oxygen availability affects both lethal and nonlethal impacts of warming on two widespread Eurasian mayflies, Ephemera danica, Müller 1764 and Serratella ignita (Poda 1761). Mayfly nymphs are often a dominant component of the invertebrate assemblage in streams, and play a vital role in aquatic and riparian food webs. In the laboratory, lethal impacts of warming were assessed under three oxygen conditions. In the field, effects of oxygen availability on nonlethal impacts of warming were assessed from mayfly occurrence in 42 293 UK stream samples where water temperature and biochemical oxygen demand were measured. Oxygen limitation affected both lethal and sublethal impacts of warming in each species. Hypoxia lowered lethal limits by 5.5 °C (±2.13) and 8.2 °C (±0.62) for E. danica and S. ignita respectively. Field data confirmed the importance of oxygen limitation in warmer waters; poor oxygenation drastically reduced site occupancy, and reductions were especially pronounced under warm water conditions. Consequently, poor oxygenation lowered optimal stream temperatures for both species. The broad concordance shown here between laboratory results and extensive field data suggests that oxygen limitation not only impairs survival at thermal extremes but also restricts species abundance in the field at temperatures well below upper lethal limits. Stream oxygenation could thus control the vulnerability of aquatic ectotherms to global warming. Improving water oxygenation and reducing pollution can provide key facets of climate change adaptation for running waters.
水生生态系统对气候变暖的响应因热效应与其他环境压力因素（如有机污染和缺氧）之间的相互作用而变得复杂。实验室实验已经证明了氧气限制如何为一些水生变温动物设定耐热性，但这仅在不切实际的致死温度下进行，且缺乏实地数据来评估氧气短缺是否也可能是亚致死性变暖效应的潜在原因。在此，我们测试了氧气供应是否会影响变暖对两种广泛分布于欧亚大陆的蜉蝣（1764年的大蜉蝣和1761年的细蜉）的致死和非致死影响。蜉蝣若虫通常是溪流中无脊椎动物群落的主要组成部分，并且在水生和河岸食物网中发挥着至关重要的作用。在实验室中，在三种氧气条件下评估了变暖的致死影响。在野外，根据英国42293个溪流样本中蜉蝣的出现情况评估了氧气供应对变暖非致死影响的作用，这些样本测量了水温及生化需氧量。氧气限制影响了每个物种变暖的致死和亚致死影响。缺氧分别使大蜉蝣和细蜉的致死温度下限降低了5.5°C（±2.13）和8.2°C（±0.62）。实地数据证实了氧气限制在温暖水域中的重要性；氧气不足会大幅降低栖息地占有率，并且在温水条件下这种降低尤为明显。因此，氧气不足降低了这两个物种的最佳溪流温度。此处实验室结果与广泛实地数据之间的广泛一致性表明，氧气限制不仅会损害极端温度下的生存能力，还会在远低于致死温度上限的温度下限制野外物种的丰度。因此，溪流的充氧可以控制水生变温动物对全球变暖的脆弱性。改善水体充氧和减少污染可为流水生态系统提供气候变化适应的关键方面。
