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正常的耐热性时，珊瑚就会白化。但白化事件通常会显示出一种无法解释的模式--相邻的珊瑚群会显示出非常不同的白化程度--从纯白色到健康珊瑚的正常棕褐色。研究人员在美属萨摩亚珊瑚礁上的280种珊瑚中观察到了这种模式，这些珊瑚已经研究了多年。这个系统将被用来测试四个主要的假设，即是什么原因导致一些珊瑚漂白，而另一些则不会：1）物种的差异，2）珊瑚经历的温度，3）它们所携带的共生体，以及4）珊瑚宿主的基因型。此外，调查人员将定期返回美属萨摩亚，测量每个珊瑚群的恢复率，并进行与上述恢复率相同的测试。白化事件留下的纯白色珊瑚礁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出现来了解珊瑚礁上的生存规则。从2015年1月开始，美属萨摩亚的珊瑚礁开始出现重大漂白事件，其中包括62种珊瑚，这些珊瑚已被深入研究珊瑚耐热性，现场温度和共生体类型。2015年4月，研究人员监测了这些珊瑚和其他珊瑚的漂白状态，共有来自四个物种的280个珊瑚，并发现物种内部和之间以及珊瑚礁区域内部和之间的漂白程度存在显着差异。该小组将通过检查自漂白事件发生前以来大约50个温度记录仪的记录来测试微气候对漂白状态的相对重要性。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。研究人员还将检查全套280个珊瑚的遗传变异，以估计漂白状态，恢复率和遗传多态性之间的关系。这些数据将用于测试微气候，共生体和珊瑚遗传学作为漂白和漂白恢复的决定因素。由于研究人员在漂白死亡之前从这280个殖民地中获得了样本，因此这项研究将提供漂白事件对珊瑚种群进化影响的第一个估计。

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.