Department of Biology, University of Pennsylvania, Philadelphia, PA, USA.
ARC Centre of Excellence for Coral Reef Studies and School of Biological Sciences, University of Queensland, St. Lucia, Qld, Australia.
Glob Chang Biol. 2021 Jun;27(12):2728-2743. doi: 10.1111/gcb.15622. Epub 2021 Apr 14.
Ocean warming is causing global coral bleaching events to increase in frequency, resulting in widespread coral mortality and disrupting the function of coral reef ecosystems. However, even during mass bleaching events, many corals resist bleaching despite exposure to abnormally high temperatures. While the physiological effects of bleaching have been well documented, the consequences of heat stress for bleaching-resistant individuals are not well understood. In addition, much remains to be learned about how heat stress affects cellular-level processes that may be overlooked at the organismal level, yet are crucial for coral performance in the short term and ecological success over the long term. Here we compared the physiological and cellular responses of bleaching-resistant and bleaching-susceptible corals throughout the 2019 marine heatwave in Hawai'i, a repeat bleaching event that occurred 4 years after the previous regional event. Relative bleaching susceptibility within species was consistent between the two bleaching events, yet corals of both resistant and susceptible phenotypes exhibited pronounced metabolic depression during the heatwave. At the cellular level, bleaching-susceptible corals had lower intracellular pH than bleaching-resistant corals at the peak of bleaching for both symbiont-hosting and symbiont-free cells, indicating greater disruption of acid-base homeostasis in bleaching-susceptible individuals. Notably, cells from both phenotypes were unable to compensate for experimentally induced cellular acidosis, indicating that acid-base regulation was significantly impaired at the cellular level even in bleaching-resistant corals and in cells containing symbionts. Thermal disturbances may thus have substantial ecological consequences, as even small reallocations in energy budgets to maintain homeostasis during stress can negatively affect fitness. These results suggest concern is warranted for corals coping with ocean acidification alongside ocean warming, as the feedback between temperature stress and acid-base regulation may further exacerbate the physiological effects of climate change.
海洋变暖导致全球珊瑚白化事件的频率增加，造成广泛的珊瑚死亡，并破坏珊瑚礁生态系统的功能。然而，即使在大规模白化事件中，许多珊瑚在暴露于异常高温的情况下也能抵抗白化。虽然白化的生理效应已有详细记录，但对于抗白化个体的热应激后果却知之甚少。此外，对于热应激如何影响可能在机体水平上被忽视但对珊瑚短期表现和长期生态成功至关重要的细胞水平过程，仍有许多需要了解。在这里，我们比较了夏威夷 2019 年海洋热浪期间抗白化和易白化珊瑚的生理和细胞反应，这是继前一次区域性白化事件 4 年后发生的重复白化事件。在两次白化事件中，种内相对白化易感性是一致的，但在热浪期间，抗白化和易白化表型的珊瑚都表现出明显的代谢抑制。在细胞水平上，在白化高峰期，易白化珊瑚的细胞内 pH 值低于抗白化珊瑚，无论是共生宿主细胞还是无共生细胞都是如此，这表明易白化个体的酸碱平衡稳态受到更大的破坏。值得注意的是，来自两种表型的细胞都无法补偿实验诱导的细胞酸中毒，这表明即使在抗白化珊瑚和含有共生体的细胞中，酸碱调节在细胞水平上也受到严重损害。因此，热干扰可能会产生重大的生态后果，因为即使是在应激期间为维持体内平衡而重新分配少量能量，也会对适应性产生负面影响。这些结果表明，对于同时面临海洋酸化和海洋变暖的珊瑚来说，需要引起关注，因为温度应激和酸碱调节之间的反馈可能会进一步加剧气候变化的生理效应。
