Data from: Effects of hypoxia and ocean acidification on the upper thermal niche boundaries of coral reef fishes

Rising ocean temperatures are predicted to cause a poleward shift in the distribution of marine fishes occupying the extent of latitudes tolerable within their thermal range boundaries. A prevailing theory suggests that the upper thermal limits of fishes are constrained by hypoxia and ocean acidification. However, some eurythermal fish species do not conform to this theory, and maintain their upper thermal limits in hypoxia. Here we determine if the same is true for stenothermal species. In three coral reef fish species we tested the effect of hypoxia on upper thermal limits, measured as critical thermal maximum (CTmax). In one of these species we also quantified the effect of hypoxia on oxygen supply capacity, measured as aerobic scope (AS). In this species we also tested the effect of elevated CO2 (simulated ocean acidification) on the hypoxia sensitivity of CTmax. We found that CTmax was unaffected by progressive hypoxia down to approximately 35 mmHg, despite a substantial hypoxia-induced reduction in AS. Below approximately 35 mmHg, CTmax declined sharply with water oxygen tension (PwO2). Furthermore, the hypoxia sensitivity of CTmax was unaffected by elevated CO2. Our findings show that moderate hypoxia and ocean acidification do not constrain the upper thermal limits of these tropical, stenothermal fishes.海洋温度上升预计将使得栖息于自身热耐受范围边界内可耐受纬度区间的海洋鱼类分布向极地偏移。主流学术理论认为，鱼类的最高热极限受低氧与海洋酸化的双重约束。但部分广温性鱼类并不遵循该理论，它们可在低氧环境下维持自身的最高热极限。本研究旨在探究狭温性鱼类是否亦存在此种特性。我们以3种珊瑚礁鱼类为研究对象，测试了以临界热极限（critical thermal maximum, CTmax）为衡量指标的低氧对鱼类最高热极限的影响。针对其中1个物种，我们还以有氧范围（aerobic scope, AS）为衡量指标，量化了低氧对其供氧能力的影响；同时针对该物种，我们还测试了高浓度CO₂（模拟海洋酸化）对CTmax低氧敏感性的影响。研究发现，尽管低氧显著降低了该物种的有氧范围，但在渐进式低氧至约35 mmHg的过程中，其临界热极限并未受到影响。当水体氧分压（PwO₂）低于约35 mmHg时，临界热极限则随水体氧分压急剧下降。此外，高浓度CO₂并未改变CTmax的低氧敏感性。本研究结果表明，适度低氧与海洋酸化并不会约束这些热带狭温性鱼类的最高热极限。