RAPID: Ecological, evolutionary and physiological responses of corals to a mass bleaching event in American Samoa

2015年1月，美属萨摩亚发生了近20年来最严重的珊瑚白化事件。当海水温度超过珊瑚的正常耐热性时，就会发生珊瑚白化。但漂白事件通常会显示出一种无法解释的模式——一个挨着一个的珊瑚群会显示出非常不同的漂白程度——从纯白色到健康珊瑚的正常褐色。研究人员在美属萨摩亚珊瑚礁上的280个珊瑚中观察到这种模式，这些珊瑚已经研究了多年。该系统将用于测试导致某些珊瑚白化而某些珊瑚不白化的四个主要假设：1)物种差异，2)珊瑚所经历的温度差异，3)它们所携带的共生体差异，以及4)珊瑚宿主的基因型差异。此外，调查人员将定期返回美属萨摩亚，以测量每个珊瑚群的恢复速度，并进行与上述相同的恢复速度测试。白化事件留下的赤裸裸的白色珊瑚礁景观是海洋变暖加剧的最常见信号之一。这项工作将利用多年的前期研究和珊瑚白化事件的到来来了解珊瑚礁的生存规则。从2015年1月开始，美属萨摩亚的珊瑚礁开始出现重大的白化事件，其中包括62种珊瑚，这些珊瑚已经被深入研究了珊瑚的耐热性、野外温度和共生体类型。2015年4月，研究人员监测了这些珊瑚和其他珊瑚的白化状况，共来自四个物种的280种珊瑚，发现了物种内部和物种之间以及珊瑚礁区域内部和区域之间的白化程度的显著差异。研究小组将通过检查大约50个温度记录仪的记录来测试小气候对白化状态的相对重要性。他们将通过检查漂白后四个时间点采集的60个菌落样本，来测试共生体类型和宿主基因表达谱的影响。研究人员还将检查280种珊瑚的遗传变异，以估计白化状态、恢复率和遗传多态性之间的关系。这些数据将用于测试小气候、共生体和珊瑚遗传学作为白化和白化恢复的决定因素。由于研究人员在漂白死亡之前从这280个群落中获得了样本，因此这项研究将首次估计漂白事件对珊瑚种群的进化影响。

The strongest coral bleaching event in nearly 20 years began in American Samoa in January 2015. Coral bleaching occurs when ocean water temperatures exceed a coral's normal heat tolerance. But bleaching events usually show an unexplained pattern - colonies next to one another can show very different levels of bleaching - from pure white to the normal tan color of a healthy coral. The investigators have observed this pattern among 280 corals on reefs in American Samoa that have been studied for years. This system will be used to test four major hypotheses about what causes some corals to bleach and some not: differences in 1) species, 2) the temperature the corals experienced, 3) the symbiont they harbor, and 4) the genotype of the coral host. In addition, the investigators will return to American Samoa at regular intervals to measure the rate of recovery of each coral colony and conduct the same tests as above for recovery rate. The stark-white reefscapes left behind by bleaching events are one of the most common signals of increased ocean warming. This work will take advantage of years of prior study and the advent of a coral bleaching event to understand the rules for survival on reefs. The reefs of American Samoa began showing a major bleaching event starting in January 2015, including 62 corals that have been intensively studied for coral thermal resistance, field temperatures, and symbiont type. In April 2015 the investigators monitored bleaching status of these and additional corals, totaling 280 corals from four species, and uncovered marked variation in bleaching extent within and between species and within and between reef regions. The team will test the relative importance of microclimate to bleaching state by examining records of approximately 50 temperature loggers in place since before the bleaching event. They will test the influence of symbiont type and host gene expression profiles by examining samples of 60 colonies taken at four time points after bleaching. The investigators will also examine the full suite of 280 corals for genetic variation to estimate the relationship between bleaching state, recovery rate and genetic polymorphism. These data will be used to test micro-climate, symbiont, and coral genetics as determinants of bleaching and bleaching recovery. Because the investigators have samples from these 280 colonies before bleaching mortality, this study will provide the first estimate for the evolutionary impact of a bleaching event on coral populations.