Reef-forming corals are under threat globally from climate change, leading to changes in sea temperatures with both hot and cold events recorded and projected to increase in frequency and severity in the future. Tolerance to heat and cold exposure has been found to be mutually exclusive in other marine invertebrates, but it is currently unclear whether a trade-off exists between hot and cold thermal tolerance in tropical corals. This study quantified the changes in physiology in Acropora millepora from the central Great Barrier Reef subjected to three temperature treatments; sub-lethal cold, ambient and sub-lethal heat (23.0 °C, 27.0 °C and 29.5 °C, respectively). After 10 weeks, pigment content and Symbiodiniaceae density increased in cold-treated corals but decreased in heat-treated corals relative to corals at ambient conditions. Heat-treated corals gained less mass relative to both ambient and cold-treated corals. These results indicate that the physiological condition of A. millepora corals examined here improved in response to mild cold exposure compared to ambient exposure and decreased under mild heat exposure despite both these temperatures occurring in situ around 15% of the year. The energetic condition of corals in the hotter treatment was reduced compared to both ambient and cooler groups, indicating that corals may be more resilient to mild cold exposure relative to mild heat exposure. The results indicate that the corals shifted their resource allocation in response to temperature treatment, investing more energy into skeletal extension rather than maintenance. No evidence of thermal tolerance trade-offs was found, and cold thermal tolerance was not lost in more heat-tolerant individuals. An enhanced understanding of physiological responses of corals at both ends of the thermal spectrum is important for predicting the resilience of corals under projected climate change conditions.

中文翻译：

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普通礁珊瑚Acropora millepora中冷热暴露的生理效应

形成珊瑚礁的珊瑚在全球范围内受到气候变化的威胁，导致海水温度发生变化，并记录了冷热事件，预计未来的频率和严重程度都会增加。已发现其他海洋无脊椎动物对热和冷暴露的耐受性是相互排斥的，但目前尚不清楚热带珊瑚的热耐受性和冷热耐受性之间是否存在权衡。本研究量化了来自大堡礁中部的 Acropora millepora 经过三种温度处理后的生理变化；亚致死冷、环境和亚致死热（分别为 23.0 °C、27.0 °C 和 29.5 °C）。10 周后，与环境条件下的珊瑚相比，冷处理珊瑚的色素含量和共生科密度增加，但热处理珊瑚的色素含量和共生科密度降低。与环境和冷处理珊瑚相比，热处理珊瑚获得的质量较少。这些结果表明，与环境暴露相比，这里检查的 A. millepora 珊瑚的生理状况在轻度寒冷暴露下有所改善，并在轻度热暴露下下降，尽管这些温度在一年中的 15% 左右都发生在原位。与环境和较冷组相比，较热处理中珊瑚的能量状况有所降低，这表明相对于轻度热暴露，珊瑚可能对轻度寒冷暴露更具弹性。结果表明，珊瑚改变了它们的资源分配以响应温度处理，将更多的能量投入到骨骼伸展而不是维护上。没有发现耐热性权衡的证据，更耐热的个体并没有丧失冷热耐受性。深入了解热谱两端珊瑚的生理反应对于预测珊瑚在预计的气候变化条件下的恢复力很重要。