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 ~35 mmHg, despite a substantial hypoxia-induced reduction in AS. Below ~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导致栖息于自身热耐受纬度范围内的海洋鱼类分布向极地迁移。当前主流理论认为，鱼类的高温上限受低氧（hypoxia）与海洋酸化（ocean acidification）的约束。然而，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高温上限。本研究旨在探究狭温性鱼类是否具备同样的特性。我们选取3种珊瑚礁鱼类，以临界热最大值（critical thermal maximum, CTmax）为指标，测试低氧对其高温上限的影响。针对其中1个物种，我们还以有氧代谢范围（aerobic scope, AS）为指标，量化了低氧对氧气供应能力的作用；同时针对该物种，测试了CO₂升高（模拟海洋酸化）对CTmax低氧敏感性的影响。研究结果显示：即便低氧诱导的有氧代谢范围出现显著下降，当水氧分压降至约35 mmHg时，CTmax仍未受明显影响；当水氧分压低于约35 mmHg时，CTmax随水氧张力（PwO2）急剧下降。此外，CO₂升高并未改变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高温上限。