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，但由于水污染和异常温暖的海水等压力而死亡，这可能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事件特别强烈，可能会在2015-16年期间漂白整个太平洋中部和东部的珊瑚。 漂白最有可能发生在南太平洋中部，也就是NSF资助的Moorea珊瑚礁长期生态研究（MCR LTER）地点的位置，从2016年2月开始。 拟议的研究将支持在MCR LTER现场进行实地实验和收集关键数据，以解决即将到来的温水事件如何与营养物污染相互作用，从而影响珊瑚漂白的流行程度和强度。 调查将集中在两个方面：（1）整个岛屿的漂白和珊瑚损失模式与整个景观的营养物质的可用性，以及（2）如何不同形式和来源的氮基营养物质可以促进或减轻漂白。 该项目将评估影响珊瑚礁的两大全球变化驱动因素-海表温度升高和营养物污染-的相互作用。 这项工作的结果可以告知资源管理者和政策制定者，来自两种不同来源（人类与鱼类来源）的两种不同形式（硝酸盐与铵）的氮富集对改变不同类型的珊瑚在主要暖水事件期间漂白的可能性的影响。 人类活动可以直接增加硝酸盐污染，并间接降低铵富集（通过捕鱼或破坏苗圃栖息地），这两种活动都可能通过增加珊瑚漂白的可能性对珊瑚产生不利影响。 因此，该项目可以提供急需的信息， 这些活动会影响珊瑚礁。 该项目将有助于培训两名研究生，他们将参加实地研究，营养物富集是改变全世界沿海生态系统的主要人为力量，特别是在珊瑚礁等贫营养系统。 基于铵与硝酸盐富集如何影响珊瑚的生理的差异，一些珊瑚礁生物学家推测，在压力下，来自人为来源的硝酸盐富集应该会削弱珊瑚-甲藻共生关系，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）和不同来源的营养素（鱼类来源与人为来源）对珊瑚生物学可能产生根本不同的影响，这可能导致它们如何改变珊瑚对温水异常漂白的敏感性产生对比效应。 此外，养分供应的空间异质性可以塑造景观尺度模式的漂白强度和随后的社区后果。 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，即海面温度升高和营养物污染。 将检验两个假设：（1）来自人为来源的硝酸盐富集将增加珊瑚对漂白的敏感性，（2）铵形式的氮将减少它。鉴于莫雷阿泻湖珊瑚礁上的大部分氮富集是人为来源，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有关的死亡率。 这些关系将探讨的三个主要属的Moorea系统（Pocillopora，鹿角珊瑚，滨珊瑚），然后按比例放大，探索全岛的漂白模式作为景观尺度异质性的功能，在养分供应。 来自实地调查和WorldView-3卫星图像的关键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用性梯度有关的漂白模式。 此外，在出现暖水异常现象之前，还将进行一次实地实验，以检验不同形式的氮对漂白可能性产生的对比效应这一假设。

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.