Adjustment of western Pacific Ocean coral reefs to sea-level rise and ocean warming

海洋温度上升和海平面上升正威胁着全世界的珊瑚礁生态系统。事实上，一些岛国的海拔不超过现代海平面1米。然而，在热带海岸修建海堤以阻挡海洋，就像在荷兰所做的那样，对小岛屿国家来说是一个巨大的经济负担。然而，健康的珊瑚礁有能力储存足够的碳酸钙，以便垂直生长并跟上海平面的上升，就像它们在地质历史上所做的那样。相比之下，受损的珊瑚礁没有能力跟上海平面的上升，使沿海社区变得脆弱，并给沿海社会造成了修建海堤的巨大经济负担。此外，就在最近，珊瑚礁正受到高水温的影响，对珊瑚造成了相当大的损害。这项研究将提出一些关键问题：西太平洋的珊瑚礁是否跟得上海平面的上升？珊瑚礁在哪里跟上了海平面的上升，是什么阻止了一些地方的珊瑚礁跟上？这项研究还将研究海洋温度的地理差异是否会影响珊瑚礁跟上海平面上升的能力。在珊瑚礁跟不上海平面上升的地方，这些天然风暴屏障将消失，导致全球数百万人失去宜居土地。这项研究的更广泛影响将集中在培训一名博士后研究员，以及在帕劳、雅普、丘克、波恩佩、科斯雷、马朱罗和基里巴斯的拟议研究地点开发和举办为期一周的培训讲习班。调查人员将与各岛屿上的当地利益攸关方合作，专注于将科学与管理实践联系起来，以减少当地对珊瑚礁的压力。珊瑚礁是世界上最多样化和最有价值的海洋生态系统之一。自约5000年前的全新世中期以来，太平洋上的珊瑚礁一直受到海平面的垂直制约。当代海平面上升正在释放这些限制，为垂直珊瑚礁的扩张提供了空间。然而，最近珊瑚一再受到热应激事件的影响，我们对现代珊瑚礁能否随着海洋温度的持续上升而“跟上”预计的未来海平面上升知之甚少。这项研究将考察太平洋从西至帕劳到东至基里巴斯的温度梯度上，珊瑚礁是否以及在哪里跟上了海平面的上升。本课程将探讨珊瑚跟上海平面的能力的空间差异，并假设珊瑚生长速度和跟上海平面上升的能力的不同将是区域温度、当地水流速度和土地利用的函数。这项研究的主要任务之一是确定每个生物礁的各种成分在地理温度梯度上对潜在碳酸盐产量的贡献。研究人员将通过测量每个研究地点每个底栖生物成分占据的空间，量化珊瑚和钙藻产生碳酸盐的速度，以及珊瑚礁破坏动物的碳酸盐破坏速度。然后，研究小组将对这些信息进行汇总，以解释珊瑚礁产生碳酸盐的总体能力。在每个研究地点，将估计可移动的底栖生物，以及棘类和草食性鱼类的计数和大小测量。研究人员将测量来自不同栖息地的不同珊瑚物种的密度，并开发出将珊瑚形态与潜在的碳酸盐沉积速率联系起来的模型。这项研究将评估海洋表面温度、流速和土地利用实践对珊瑚礁应对海平面上升的能力的贡献。将使用两种不同的方法来预测碳酸盐产量和海平面上升之间的关系。第一个模型将假设垂直珊瑚礁的吸积能力与波利茨微型环礁在不同岛屿位置的延伸直接相关。第二个模型将采用分层贝叶斯方法来研究珊瑚礁的生长，这取决于钙化生物的存在和密度，以及物理、化学和生物侵蚀过程。

Increases in ocean temperatures and sea-level rise are threatening coral reef ecosystems worldwide. Indeed, some island nations are no more than 1 m above modern sea level. Yet, building sea walls on tropical coasts, to keep out the ocean, as they do in the Netherlands, is a substantial economic burden on small-island nations. Healthy coral reefs, however, have the capacity to lay down sufficient calcium carbonate to grow vertically and keep up with sea-level rise, as they did in the geological past. By contrast, damaged coral reefs do not have the capacity to keep up with sea-level rise, making the coastal communities vulnerable, and inflicting a large economic burden on the coastal societies to build sea walls. In addition, and very recently, coral reefs are being subjected to high water temperatures that are causing considerable damage to corals. This study will ask some critical questions: Are coral reefs in the western Pacific Ocean keeping up with sea-level rise? Where are reefs keeping up with sea-level rise, and what is preventing reefs in some localities from keeping up? This study will also examine whether geographical differences in ocean temperatures influence the capacity of reefs to keep up with sea-level rise. Where coral reefs cannot keep up with sea-level rise, these natural storm barriers will disappear, resulting in the loss of habitable land for millions of people worldwide. The broader impacts of the study will focus on training a post-doctoral researcher, and developing and running one-week training workshops in the proposed study locations in Palau, Yap, Chuuk, Pohnpei, Kosrae, Majuro, and Kiribati. The investigators will work with local stakeholders on the various islands, focusing on connecting science to management practices to reduce local stressors to coral reefs. Coral reefs are one of the world's most diverse and valuable marine ecosystems. Since the mid-Holocene, some 5000 years ago, coral reefs in the Pacific Ocean have been vertically constrained by sea level. Contemporary sea-level rise is releasing these constraints, providing accommodation space for vertical reef expansion. Yet recently corals have been repeatedly subjected to thermal-stress events, and we know little about whether modern coral reefs can "keep up" with projected future sea-level rise as the ocean temperatures continue to increase. This study will examine whether and where coral reefs are keeping up with sea-level rise across a temperature gradient in the Pacific Ocean, from Palau in the west to Kiribati in the east. The spatial differences in the capacity to keep up with sea level will be explored, and it is hypothesized that differential rates of coral growth and capacity to keep up with sea-level rise will be a function of regional temperatures, local water-flow rates, and land-use. One of the major tasks of this study is to determine the contribution of the various components of each reef to potential carbonate production, across the geographical temperature gradient. The investigators will quantify the rates of carbonate production, by corals and calcareous algae, and the rates of carbonate destruction, by reef eroders, by measuring the space occupied by each benthic component at each study site. The team will then sum that information to interpret the overall capacity of the reef to produce carbonate. At each study site mobile benthic eroders will be estimated, as counts and size measurements of echinoids and herbivorous fishes. The investigators will measure the densities of the different coral species, from different habitats, and develop models that relate the coral morphologies with the potential rate of carbonate deposition. This study will assess the contribution of sea surface temperature, flow rates, and land-use practice to the capacity of reefs to keep up with sea-level rise. Two different approaches will be used to predict the relationship between carbonate production and sea-level rise. The first model will assume that the capacity of vertical reef accretion is directly related to the extension of Porites microatolls at the various island locations. The second model will take a hierarchical Bayesian approach to examine reef growth, which depends on the presence and density of calcifying organisms, and on physical, chemical, and biological erosional processes.