Reef-building corals living in extreme environments can provide insight into the negative effects of future climate scenarios. In hot environments, coral communities experience disproportionate thermal stress as they live very near or at their upper thermal limits. This results in a high frequency of bleaching episodes, but it is unknown whether temperature-driven outbreaks of coral disease follow a similar trajectory. Here we tracked outbreaks of a white-syndrome (WS) disease over three years in the hottest region inhabited by reef-building corals, the southern Persian Gulf. From 2014 to 2016, WS affected 10 of the 16 scleractinian genera recorded at inshore and offshore sites. Intra- and inter-specific transmission of lesions was frequently observed, indicative of a single contagious disease infecting multiple coral taxa. Colonies of Acropora were the most susceptible to WS disease and were more than twice as likely to experience lesions than any other genera. Prevalence reached 42% of Acropora colonies and lesions progressed at an average rate of 1 mm day −1 . Platygyra colonies were the second most susceptible to WS disease, where prevalence reached 33% and lesions progressed at 0.3 mm day −1 . Affected colonies of both of these genera suffered considerable partial mortality that was not recovered between years, promoting the fragmentation of larger colonies into smaller size classes. Across the 3 years of our study, the onset of WS outbreaks occurred early in summer and prevalence increased exponentially with cumulative heat exposure (coral community r 2 = 0.55, Acropora r 2 = 0.72, Platygyra r 2 = 0.75). Peak levels of community-wide prevalence occurred in August (10% of all coral colonies) to September (14%) when preceding 4-week and 8-week average temperatures exceeded 34.5 °C and 34 °C, respectively. Outbreaks ceased following the return of cooler temperatures with prevalence remaining below 0.5% between December and June. Levels of bleaching remained relatively low (< 5% prevalence), despite exposure to daily temperatures ≥ 35 °C each summer. These findings demonstrate that thermal stress on coral reefs does not always manifest as coral bleaching and diseases can present as a primary sign of thermal stress. Consequently, temperature-driven outbreaks of coral disease are expected to become more widespread as climate warming pushes corals to be living increasingly closer to their upper thermal limits.

中文翻译：

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珊瑚病的年度爆发与极端的季节性变暖相吻合

生活在极端环境中的造礁珊瑚可以深入了解未来气候情景的负面影响。在炎热的环境中，珊瑚群落会经历不成比例的热应力，因为它们非常接近或处于热极限。这导致了高频率的白化事件，但尚不清楚温度驱动的珊瑚病爆发是否遵循类似的轨迹。在这里，我们追踪了三年来在珊瑚礁栖息的最热地区波斯湾南部爆发的一种白人综合症 (WS) 疾病。从 2014 年到 2016 年，WS 影响了在近海和近海地点记录的 16 个石珊瑚属中的 10 个。经常观察到病灶的种内和种间传播，表明一种传染病感染了多种珊瑚分类群。鹿角珊瑚群对 WS 病最敏感，并且比任何其他属都发生病变的可能性高出两倍以上。盛行率达到 42% 的鹿角珊瑚菌落，病变以平均 1 毫米天 -1 的速度发展。Platygyra 菌落是第二个最易患 WS 疾病的群体，其患病率达到 33%，并且病变在第 -1 天 0.3 毫米时进展。这两个属的受影响菌落都遭受了相当大的部分死亡，而且在几年之间没有恢复，促使较大的菌落分裂成较小的规模。在我们研究的 3 年中，WS 暴发发生在夏初，流行率随着累积热量暴露呈指数增长（珊瑚群落 r 2 = 0.55，鹿角珊瑚 r 2 = 0.72，Platygyra r 2 = 0.75）。当前 4 周和 8 周的平均温度分别超过 34.5 °C 和 34 °C 时，社区范围内流行率的峰值发生在 8 月（占所有珊瑚群的 10%）至 9 月（14%）。随着气温回升，疫情停止，12 月至 6 月期间流行率保持在 0.5% 以下。尽管每年夏天每天都暴露在 ≥ 35 °C 的温度下，但漂白的水平仍然相对较低（流行率 < 5%）。这些发现表明，珊瑚礁上的热应激并不总是表现为珊瑚白化，疾病可能是热应激的主要迹象。因此，随着气候变暖促使珊瑚越来越接近其温度上限，预计温度驱动的珊瑚病爆发将变得更加普遍。