RAPID: How does nutrient availability alter coral bleaching, mortality, and recovery on Moorea coral reefs?

珊瑚礁具有巨大的社会和生态价值，但会因水污染和异常温暖的海水等压力而死亡，这可能会导致珊瑚漂白和死亡。美国国家海洋和大气管理局预测，目前的暖水厄尔尼诺现象特别强烈，可能会在2015-16年间漂白中太平洋和东太平洋的珊瑚。白化最有可能发生在南太平洋中部，那里是NSF资助的Moorea珊瑚礁长期生态研究(MCR LTER)地点，从2016年2月开始。拟议的研究将支持在MCR LTER地点进行实地实验和收集关键数据，以解决即将到来的暖水事件如何与营养污染相互作用，影响珊瑚漂白的普遍性和强度。调查将集中于两个方面：(1)全岛范围内漂白和珊瑚损失的模式，以及(2)不同形式和来源的氮基营养如何促进或减轻漂白。该项目将评估两个主要的全球变化驱动因素对珊瑚礁的相互作用，这两个驱动因素是海洋表面温度上升和营养物质污染。这项工作的结果可以让资源经理和政策制定者了解来自两种不同来源(人和鱼)的两种不同形态的氮(硝酸盐和铵)对改变不同类型珊瑚在重大暖水事件期间漂白的可能性的影响。人类活动可直接增加硝酸盐污染，并间接降低氨氮富集度(通过捕鱼或破坏苗圃栖息地)，这两者都可能通过增加珊瑚漂白的可能性而对其产生不利影响。因此，该项目可以提供关于人类活动如何影响珊瑚礁的急需信息。该项目将帮助培训两名将参与实地研究的研究生。营养丰富是改变世界各地沿海生态系统的主要人为力量，特别是在珊瑚礁等低营养系统中。根据氨氮和硝酸盐富集对珊瑚生理影响的不同，一些珊瑚礁生物学家推测，在压力下，人为来源的硝酸盐富集会削弱珊瑚和甲藻的共生，而珊瑚鱼排泄的循环氮可能是有益的。因此，不同形式的氮(硝酸盐与铵)和不同的营养来源(鱼源与人为)可能对珊瑚生物学产生根本不同的影响，这可能导致在它们如何改变珊瑚对暖水异常漂白的敏感性方面产生不同的影响。此外，养分有效性的空间异质性可能会在漂白强度和随后的群落后果方面形成景观尺度格局。这项研究将评估两个主要的全球变化驱动因素对珊瑚礁的相互作用，即海洋表面温度上升和营养物质污染。将检验两个假设：(1)来自人为来源的硝酸盐丰富将增加珊瑚对漂白的敏感性，(2)以铵的形式存在的氮将减少珊瑚的漂白。鉴于莫雷亚泻湖珊瑚礁上的氮浓缩大部分是人为来源，研究人员进一步假设，在景观尺度上，与营养贫乏地点的珊瑚相比，营养丰富地点的珊瑚将导致更大的漂白和与漂白相关的死亡。这些关系将探索莫雷亚系统中的三个主要属(Pocillopora，Acropora，Porites)，然后扩大规模，探索全岛范围内的漂白模式，作为景观尺度养分可获得性的异质性的函数。来自实地调查和WorldView-3卫星图像的重要漂白前数据将与随后的漂白后数据配对，以探索与珊瑚礁复合体营养物质可获得性梯度有关的漂白模式。此外，在温水异常之前，将启动一项现场实验，以检验不同形式的氮将对漂白可能性产生不同影响的假设。

Coral reefs have enormous social and ecological value but are killed by such stresses as water pollution and unusually warm water, which can cause corals to bleach and die. The National Oceanic and Atmospheric Administration has predicted that the current warm-water El Niño event is especially strong and will likely bleach corals across the central and eastern Pacific during 2015-16. Bleaching is most likely to occur in the central South Pacific, the location of the NSF-funded Moorea Coral Reef Long Term Ecological Research (MCR LTER) site, starting in February 2016. The proposed research will support field experiments and collection of key data at the MCR LTER site to address how the coming warm-water event interacts with nutrient pollution to influence the prevalence and intensity of coral bleaching. The investigation will focus on two aspects: (1) island-wide patterns in bleaching and coral loss with respect to nutrient availability across the landscape, and (2) how different forms and sources of nitrogen-based nutrients can either facilitate or mitigate bleaching. The project will assess the interaction of two major global change drivers on coral reefs, elevated sea surface temperature and nutrient pollution. Results from this work can inform resource managers and policy makers regarding the effects of nitrogen enrichment in two different forms (nitrate vs. ammonium) from two different sources (human- vs. fish-derived) on altering the probability different types of corals will bleach during major warm-water events. Human activities can enhance nitrate pollution directly, and lower ammonium enrichment indirectly (via fishing or destruction of nursery habitat), both of which might adversely affect corals by increasing the probability they will bleach. As such, the project can provide much-needed information about how human activities can impact coral reefs. The project will contribute to the training of two graduate students who will participate in the field research.Nutrient enrichment is a major anthropogenic force altering coastal ecosystems worldwide, particularly in oligotrophic systems such as coral reefs. Based on differences in how ammonium versus nitrate enrichment affect the physiology of corals, some coral reef biologists have speculated that under stress, nitrate enrichment from anthropogenic sources should weaken the coral-dinoflagellate symbiosis, whereas recycled nitrogen excreted by reef fishes could be beneficial. Thus, different forms of nitrogen (nitrate vs. ammonium) and different sources of nutrients (fish-derived vs. anthropogenic) can have fundamentally different effects on coral biology, which may lead to contrasting effects on how they alter the susceptibility of coral to bleaching from warm-water anomalies. Further, spatial heterogeneity in nutrient availability could shape landscape scale patterns in the intensity of bleaching and subsequent community consequences. This research will assess the interaction of two major global change drivers on coral reefs, elevated sea surface temperature and nutrient pollution. Two hypotheses will be tested: (1) that nitrate enrichment from anthropogenic sources will increase the susceptibility of corals to bleaching, and (2) that nitrogen in the form of ammonium will reduce it. Given that much of the N enrichment on the reefs in the lagoons of Moorea is of anthropogenic origin, the investigators further hypothesize that on a landscape scale, corals in more nutrient enriched sites will incur greater bleaching and bleaching-associated mortality compared to corals at nutrient poor sites. These relationships will be explored for the three major genera in the Moorea system (Pocillopora, Acropora, Porites), and then scaled up to explore island-wide patterns of bleaching as a function of landscape scale heterogeneity in nutrient availability. Crucial pre-bleaching data from field surveys and WorldView-3 satellite imagery will be paired with subsequent post-bleaching data to explore bleaching patterns in relation to gradients in nutrient availability on the reef complex. In addition, a field experiment will be initiated prior to the warm-water anomaly to test the hypothesis that different forms of nitrogen will have contrasting effects on the likelihood of bleaching.