Ocean Acidification-Category 1: Collaborative Research: An Investigation of the Role of Nutrition in the Coral Calcification Response to Ocean Acidification

知识价值：在本世纪，所有热带珊瑚礁生态系统，无论是人口稠密的海岸线边缘，还是偏远岛屿和环礁的边缘，都面临着大气二氧化碳水平上升导致的海洋酸化的前所未有的威胁。在迄今为止进行的许多实验室实验中，硬质珊瑚(石珊瑚)产生的碳酸钙(钙化)与海水饱和状态(OMEGAar)呈负相关，无论OMEGAar是通过酸还是添加二氧化碳来控制的。根据这些数据，预计到本世纪末，珊瑚钙化率可能会下降高达现代价值的80%。然而，越来越多的新实验数据表明，珊瑚钙化对海洋酸化的反应可能不那么直接，而且比之前认识到的更具变异性。在包括我们自己在内的至少10个最近的实验中，8个不同的热带和温带物种在营养充足但显著升高的二氧化碳条件下(780-1200ppm，OMEAGar~1.5-2)继续以与环境二氧化碳下饲养的同种植物相当的速度钙化。这些实验结果与在东太平洋和阿曼南部珊瑚礁上收集的初步现场数据一致，这些珊瑚今天在相当于工业化前二氧化碳2倍和3倍的条件下生活和共生骨骼。在这些高二氧化碳、高营养珊瑚礁(硝酸盐浓度通常超过2.5微摩尔)上，珊瑚的生长速度与低二氧化碳、少营养珊瑚礁环境中的同类珊瑚的生长速度相当，有时甚至超过。研究人员提出，珊瑚的能量状态与无机养分和/或食物的可获得性密切相关，是对二氧化碳诱导的海洋酸化的钙化反应的关键因素。如果他们的假设得到这里提出的实验室和实地调查的证实，这意味着，在气候对海洋分层的影响和沿海地区人类活动增加的推动下，预测的本世纪沿海和开阔海洋营养物质浓度的变化可能在加剧和在某些地区调节珊瑚礁对海洋酸化的反应方面发挥关键作用。这项研究计划建立在调查人员的初步结果和观察结果的基础上。这一实验室和现场相结合的计划将检验以下假设：1.珊瑚钙化对海洋酸化的反应与珊瑚宿主的能量状态有关。共生体光合作用和异养摄食对珊瑚能量状态的相对贡献因物种而异。无论是通过无机营养刺激光合作用还是通过寄主的直接异养摄食来提高在高二氧化碳下饲养的珊瑚的能量状态，都可以降低钙化对海水OMEGAar减少的敏感性。2.存在一个物种特有的二氧化碳阈值水平，超过这个阈值，能量状态的增强不再能补偿外部海水OMEGAAR的下降。类似地，我们将测试一个假设，即存在一个营养阈值，超过该阈值，即使在高二氧化碳条件下，营养物质也会对钙化不利。3.温度诱导的藻类共生体减少是降低珊瑚宿主能量储备、加剧钙化对海洋酸化反应的应激源之一。4.对钙化对海洋酸化反应的营养调节今天已经在珊瑚礁上发生，并使自然高欧米伽/低营养礁石上的珊瑚能够像自然低欧米伽/高营养条件的珊瑚礁上的珊瑚一样快速生长。在实验室和自然野外验证这些发现，并确定一系列物种的营养和二氧化碳阈值，将对预测高二氧化碳世界中的珊瑚礁弹性产生直接的直接影响。我们的项目汇集了珊瑚生物地球化学、化学海洋学、分子生物学和珊瑚生殖生态学方面的各种专业知识，专注于一个具有巨大社会、经济和保护意义的问题。除了支持4个PI的实验室，它还通过普林斯顿-基本输入输出系统学生暑期实习计划资助一名研究生研究员、一名博士后研究员和本科生培训。所有研究都将在国家和国际会议和讲习班上介绍，并通过生物和化学海洋学数据管理办公室的出版物和档案及时传播数据。

Intellectual Merit: Over the course of this century, all tropical coral reef ecosystems, whether fringing heavily populated coastlines or lining remote islands and atolls, face unprecedented threat from ocean acidification caused by rising levels of atmospheric CO2. In many laboratory experiments conducted to date, calcium carbonate production (calcification) by scleractinian (stony) corals showed an inverse correlation to seawater saturation state OMEGAar), whether OMEGAar was manipulated by acid or CO2 addition. Based on these data, it is predicted that coral calcification rates could decline by up to 80% of modern values by the end of this century. A growing body of new experimental data however, suggests that the coral calcification response to ocean acidification may be less straightforward and a lot more variable than previously recognized. In at least 10 recent experiments including our own, 8 different tropical and temperate species reared under nutritionally-replete but significantly elevated CO2 conditions (780-1200 ppm, OMEAGar ~1.5-2), continued to calcify at rates comparable to conspecifics reared under ambient CO2. These experimental results are consistent with initial field data collected on reefs in the eastern Pacific and southern Oman, where corals today live and accrete their skeletons under conditions equivalent to 2X and 3X pre-industrial CO2. On these high CO2, high nutrient reefs (where nitrate concentrations typically exceed 2.5 micro-molar), coral growth rates rival, and sometimes even exceed, those of conspecifics in low CO2, oligotrophic reef environments.The investigators propose that a coral's energetic status, tightly coupled to the availability of inorganic nutrients and/or food, is a key factor in the calcification response to CO2-induced ocean acidification. Their hypothesis, if confirmed by the laboratory and field investigations proposed here, implies that predicted changes in coastal and open ocean nutrient concentrations over the course of this century, driven by both climate impacts on ocean stratification and by increased human activity in coastal regions, could play a critical role in exacerbating and in some areas, modulating the coral reef response to ocean acidification. This research program builds on the investigators initial results and observations. This combined laboratory and field program will test the hypothesis that: 1. The coral calcification response to ocean acidification is linked to the energetic status of the coral host. The relative contribution of symbiont photosynthesis and heterotrophic feeding to a coral's energetic status varies amongst species. Enhancing the energetic status of corals reared under high CO2, either by stimulating photosynthesis with inorganic nutrients or by direct heterotrophic feeding of the host lowers the sensitivity of calcification to decreased seawater OMEGAar. 2. A species-specific threshold CO2 level exists over which enhanced energetic status can no longer compensate for decreased OMEGAar of the external seawater. Similarly, we will test the hypothesis that a nutrient threshold exists over which nutrients become detrimental for calcification even under high CO2 conditions. 3. Temperature-induced reduction of algal symbionts is one stressor that can reduce the energetic reserve of the coral host and exacerbate the calcification response to ocean acidification. 4. Nutrient modulation of the calcification response to ocean acidification already occurs on reefs today and enables corals on naturally high OMEGA/low nutrient reefs to grow as fast as conspecifics on reefs with naturally low OMEGA/high nutrient conditions.Broader Impacts: The investigator's initial findings highlight the critical importance of energetic status in the coral calcification response to ocean acidification. Verification of these findings in the laboratory and at natural field sites, and identification of nutrient and CO2thresholds for a range of species will have immediate, direct impact on predictions of reef resilience in a high CO2 world. Our project brings together a diverse group of expertise in coral biogeochemistry, chemical oceanography, molecular biology and coral reproductive ecology to focus on a problem that has enormous societal, economic and conservation relevance. In addition to supporting the labs of 4 PIs, it funds a graduate research fellow, a post-doctoral investigator and undergraduate training through the Princeton-BIOS Student Summer Internship Program. All research will be presented at national and international meetings and workshops and data disseminated in a timely manner through publications and archiving in the Biological and Chemical Oceanographic Data Management office.