Toward Predicting the Impact of Ocean Acidification on Net Calcification by a Broad Range of Coral Reef Ecosystems: Identifying Patterns and Underlying Causes

知识价值：我们对海洋酸化对珊瑚礁钙化影响的理解大部分来自实验室操作实验，在这些实验中，珊瑚礁生物从它们的自然栖息地移走，并在预计本世纪末热带海洋碳酸钙饱和度（Omega）的条件下饲养。相比之下，描述珊瑚礁生态系统对碳酸钙饱和度变化敏感性的原位数据缺乏。然而，新出现的证据表明，在碳酸钙饱和度变化程度相同的情况下，培养生物的钙化反应与珊瑚礁生态系统的净钙化反应之间可能存在关键差异。在大多数情况下，网礁钙化对碳酸钙饱和度变化的敏感性比实验室操作实验预测的更为严重。显然，对珊瑚礁生态系统对21世纪海洋酸化反应的准确预测将取决于对生态系统规模反应的有力表征和对形成这些反应的基本过程的理解。利用现有数据，研究人员发现，珊瑚礁生态系统钙化对三角洲碳酸钙饱和度的敏感性符合经验速率方程R=k(Aragonite saturation state-1) n，该方程也描述了净非生物源CaCO3沉淀速率(R)与文石过饱和程度（Aragonite saturation state-1）之间的关系。这意味着，净生态系统钙化（NEC）对海洋酸化的响应受物理化学基本定律的支配，并且可能跨越空间和时间进行预测。从这个角度来看，NEC现有的数据集（尽管稀疏）揭示了不同的模式，如果得到验证，将对不同的珊瑚礁生态系统如何应对21世纪的海洋酸化产生重要影响。研究人员已经拟定了一个以这一命题为基础的研究计划。该项目扩展了目前在四个战略地点的生态系统尺度观测数据集，使我们能够测试以下假设：珊瑚礁生态系统钙化对三角洲文石饱和状态的敏感性（速率方程中的“n”）随着文石饱和状态的降低而降低。这意味着，随着本世纪海洋酸化的进程，珊瑚礁钙化下降的速度将放缓。2. 钙化群落的能量状态是生态系统净钙化绝对速率（速率方程中的“k”）的关键决定因素，它与n结合，定义了文石饱和状态值，当NEC接近于零时。由此可见，在健康的、能量充沛的珊瑚礁生态系统中，从净钙化到净溶解的转变将被推迟，而在受到干扰的、能量枯竭的生态系统中，这种转变将加速。3. 优势珊瑚礁钙化物（珊瑚和藻类）个体的钙化反应弱于测量的生态系统尺度对文石饱和状态相同变化的响应。由此可见，在实验室实验中未充分捕捉到的过程，如生物侵蚀和溶解，将在珊瑚礁对海洋酸化的反应中发挥重要作用。更广泛的影响：海洋酸化威胁到全球5亿人的生计，他们依靠珊瑚礁提供可居住和农业用地、食物、建筑材料、海岸保护和旅游业收入。然而，来自海洋酸化（OA）研究的数据表明，我们对珊瑚礁生态系统规模对OA的反应的认识存在严重差距，这限制了我们预测其对世界不同地区不同珊瑚礁影响的时间和严重程度的能力。利用研究人员和其他人产生的现有数据，该项目将解决一系列相关假设，如果研究证实，将对高二氧化碳世界中珊瑚礁恢复力的预测产生直接影响。该项目汇集了珊瑚礁生物地球化学、化学海洋学和物理海洋学方面的专业知识，专注于一个具有巨大社会、经济和保护意义的问题。为一名年轻的研究者提供支持，本科生和少数民族学生将通过WHOI夏季奖学金计划、伍兹霍尔海洋教育协会和PEP计划参与研究，并将加强私人机构与太平洋岛屿保护组织和利益相关者之间的迅速合作，其目标是确保保护决策以科学数据为基础。研究结果将在国家和国际会议和讲习班上提出，并通过同行审查的出版物及时传播。通过该计划产生的所有数据将存档在生物和化学海洋学数据管理办公室（BCO-DMO）和泛大陆开放获取图书馆。

Intellectual Merit: Much of our understanding of the impact of ocean acidification on coral reef calcification comes from laboratory manipulation experiments in which reef organisms are removed from their natural habitat and reared under conditions of calcium carbonate saturation (Omega) predicted for the tropical oceans at the end of this century. By comparison, there is a paucity of in situ data describing the sensitivity of coral reef ecosystems to changes in calcium carbonate saturation. Yet emerging evidence suggests there may be critical differences between the calcification response of organisms in culture and the net calcification response of a coral reef ecosystem, to the same degree of change in calcium carbonate saturation. In the majority of cases, the sensitivity of net reef calcification to changing calcium carbonate saturation is more severe than laboratory manipulation experiments predict. Clearly, accurate predictions of the response of coral reef ecosystems to 21st century ocean acidification will depend on a robust characterization of ecosystem-scale responses and an understanding of the fundamental processes that shape them. Using existing data, the investigators show that the sensitivity of coral reef ecosystem calcification to Delta calcium carbonate saturation conforms to the empirical rate equation R=k(Aragonite saturation state -1)n, which also describes the relationship between the rate of net abiogenic CaCO3 precipitation (R) and the degree of aragonite supersaturation (Aragonite saturation state-1). By implication, the net ecosystem calcification (NEC) response to ocean acidification is governed by fundamental laws of physical chemistry and is potentially predictable across space and time. When viewed this way, the existing, albeit sparse, dataset of NEC reveals distinct patterns that, if verified, have important implications for how different coral reef ecosystems will respond to 21st century ocean acidification. The investigators have outlined a research program designed to build on this proposition. The project expands the currently sparse dataset of ecosystem-scale observations at four strategically placed reef sites, enabling us to test the following hypotheses: 1. The sensitivity ("n" in the rate equation) of coral reef ecosystem calcification to Delta Aragonite saturation state decreases with decreasing Aragonite saturation state. By implication, the rate at which reef calcification declines will slow as ocean acidification progresses over the course of this century. 2. The energetic status of the calcifying community is a key determinant of absolute rates of net ecosystem calcification ("k" in the rate equation), which, combined with n, defines the Aragonite saturation state value at which NEC approaches zero. By implication, the shift from net calcification to net dissolution will be delayed in healthy, energetically replete coral reef ecosystems and accelerated in perturbed, energetically depleted ecosystems. 3. The calcification response of individual colonies of dominant reef calcifiers (corals and algae) is weaker than the measured ecosystem-scale response to the same change in Aragonite saturation state. By implication, processes not adequately captured in laboratory experiments, such as bioerosion and dissolution, will play an important role in the coral reef response to ocean acidification. Broader Impacts: Ocean acidification threatens the livelihoods of 500 million people worldwide who depend on coral reefs to provide habitable and agricultural land, food, building materials, coastal protection and income from tourism. Yet data emerging from ocean acidification (OA) studies point to critical gaps in our knowledge of reef ecosystem-scale responses to OA that currently limit our ability to predict the timing and severity of its impact on different reefs in different parts of the world. Using existing data generated by the investigators and others, this project will address a series of related hypotheses, which, if verified by the research, will have an immediate, direct impact on predictions of coral reef resilience in a high CO2 world. This project brings together expertise in coral reef biogeochemistry, chemical oceanography and physical oceanography to focus on a problem that has enormous societal, economic and conservation relevance. Support is provided for a young investigator, undergraduate and minority student will participate in research through the WHOI Summer Fellowship Program, the Woods Hole Sea Education Association and PEP programs, and a burgeoning collaboration will be enhanced between the PIs and Pacific Island conservation groups and stakeholders whose goal it is to ensure that conservation decisions are grounded in scientific data. Results of the study will be presented at national and international meetings and workshops and disseminated in a timely manner through peer-reviewed publications. All data produced through this program will be archived in the Biological and Chemical Oceanographic Data Management Office (BCO-DMO) and the Pangaea Open Access library.