Constraining Thermal Thresholds and Projections of Temperature Stress on Pacific Coral Reefs Over the 21st Century: Method Refinement and Application

21 世纪太平洋珊瑚礁温度应力的约束热阈值和预测：方法改进和应用

• 批准号: 1031971
• 负责人: Anne Cohen
• 金额: $ 57万
• 依托单位: Woods Hole Oceanographic Institution
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2010
• 资助国家: 美国
• 起止时间: 2010-10-01 至 2014-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1031971&HistoricalAwards=false
• 关键词: Constraining; Thermal; Thresholds; Projections; Temperature; Constraining; Thermal; Thresholds; Projections; Temperature

Sea surface temperature (SST) across much of the global tropics has increased by 0.5-1 degrees C in the past 4 decades and, with it, the frequency and geographic extent of coral bleaching events and reef mortality. As levels of atmospheric CO2 continue to rise, there is mounting concern that CO2-induced climate change will pose the single greatest threat to the survival of coral reefs. Averaged output of 21 IPCC climate models for a mid-range CO2 emissions scenario predicts that tropical SSTs will increase another 1.5-3 degrees C by the end of this century. Combined with current estimates of thermal thresholds for coral bleaching, the outlook for the future of coral-reef ecosystems, worldwide, appears bleak. There are several key issues that limit accurate predictions of the full and lasting impact of rising SSTs. These include (1) level of confidence in the spatial and temporal patterns of the predicted warming, (2) knowledge of thermal thresholds of different reef-building coral species, and (3) the potential for corals to increase resistance to thermal stress through repeated exposure to high temperature events. New skeletal markers have been developed that constrain the thermal thresholds and adaptive potential of multiple, individual coral colonies across 3-D space and through time. The method, based on 3-D CAT scan reconstructions of coral skeletons, has generated initial data from two coral species in the Red Sea, Great Barrier Reef and Phoenix Islands. Results showed that large, abrupt declines in skeletal growth occur at thresholds of accumulated heat stress defined by NOAA's Degree Heating Weeks Index (DHWs). In addition, there was a significant correlation between host lipid reserve, an independent measure of stress and mortality risk, and rates of skeletal growth. Because the coral skeleton archives the history of each coral's response to and recovery from successive, documented thermal anomalies, this approach pinpoints the thermal thresholds for sub-lethal impacts, the recovery time (if any) following a return to normal oceanographic conditions, and tests for a dampened response following successive events, indicative of acclimation. This research program builds on initial work, focusing on method refinement and application to corals on two central Pacific reefs. With contrasting thermal histories, these reefs are considered at greatest risk from future ocean warming. In parallel, new experiments will be run on an ocean general-circulation model (OGCM) that is well suited to the tropical Pacific and of sufficiently high resolution, both horizontal and vertical, to maximize projections of thermal stress on specific central Pacific Reef sites over the next few decades. The OGCM output will also be of sufficient temporal resolution to compute DHWs, thus addressing a major limitation of the direct application of global climate model output (as archived for the IPCC AR4) toward coral-reef studies. Specifically, this study will: (1) collect multiple new, medium-length (15-30 yrs) cores and branches from two dominant reef-building species at 1-30m depth in the Gilbert and Jarvis Islands, central tropical Pacific; (2) apply 3-D CAT scanning and image analysis techniques to quantify systematically thermal thresholds, rates of recovery and resilience for each species, at each reef site and with depth; (3) quantify energetic reserve and symbiont genotype amongst thermally more- and less- resilient colonies, establishing a quantitative link between calcification stress and mortality risk, and determining the physiological basis for calcification responses to thermal stress; (4) use an OGCM specifically tailored to the tropical Pacific to produce a dynamically consistent set of forecasts for near-term climate change at the target reef sites; and (5) combine coral data with model output and refine the projected thermal stress forecast, in degree heating weeks, for corals in this central Pacific Island group over the 21st century. This project includes funding for a young investigator, a postdoctoral investigator, a graduate student, and several undergraduate researchers through WHOI's summer student fellowship program. Because the method of quantifying thermal thresholds and recovery rates can be applied relatively efficiently and inexpensively to generate data for many different coral species across large spatial scales, an anticipated successful outcome will promote collection of similar data from other Pacific reefs. This data "network," when combined with the weekly-resolved OGCM output, will enable species and depth-specific projections of coral responses to thermal stress on individual reefs across the tropical Pacific over the 21st century. All research will be presented at national and international meetings and at public venues; results will be summarized on websites, and will be integrated into undergraduate and graduate courses by the Co-PIs.

在过去的40年中，整个全球热带地区的海面温度（SST）在0.5-1摄氏度上增加了0.5-1摄氏度，并且随之而来的是珊瑚漂白事件和珊瑚礁死亡率的频率和地理范围。随着大气二氧化碳的水平继续上升，人们一直担心二氧化碳引起的气候变化将对珊瑚礁的生存构成最大的威胁。对于中范围的二氧化碳排放方案的21个IPCC气候模型的平均输出预测，到本世纪末，热带SST将增加1.5-3摄氏度。结合当前对珊瑚漂白的热阈值的估计值，全球珊瑚Reef生态系统未来的前景似乎都令人沮丧。有几个关键问题限制了对SST上升的全部和持久影响的准确预测。其中包括（1）对预测变暖的空间和时间模式的信心水平，（2）了解不同礁石建造珊瑚种类的热阈值的知识，以及（3）珊瑚通过反复暴露于高温事件而增加对热应力的潜力。已经开发出了新的骨骼标记，从而限制了跨3-D空间和随时间的多个单个珊瑚菌落的热阈值和自适应潜力。该方法基于珊瑚骨骼的3-D CAT扫描重建，已从红海中的两个珊瑚物种，大屏障礁和凤凰岛产生了初始数据。结果表明，骨骼生长的大量下降发生在NOAA学位加热周数指数（DHWS）定义的累积热应力的阈值下。此外，宿主脂质储备之间存在着显着的相关性，对压力和死亡风险的独立衡量以及骨骼生长的速度。由于珊瑚骨架构成了每个珊瑚对连续的，记录的热异常的响应和恢复的历史，因此这种方法指出了亚致死撞击的热阈值，恢复到正常的海洋学条件后的恢复时间（如果有），并测试了连续响应后遇到的潮湿事件的恢复时间，表明了Acclimation Acclimation。该研究计划以初始工作为基础，重点介绍了两个中太平洋礁石上的珊瑚的方法和应用。与对比的热历史相比，这些珊瑚礁被认为是未来海洋变暖的最大风险。同时，新实验将在海洋通用模型（OGCM）上进行，该模型非常适合热带太平洋，并且在水平和垂直方向上都具有足够的高分辨率，以最大程度地提高未来几十年中特定中太平洋礁石地点的热应力投影。 OGCM输出也将具有足够的时间分辨率来计算DHW，从而解决了全球气候模型输出（如IPCC AR4的存档）直接应用于珊瑚Reef研究的主要限制。具体而言，这项研究将：（1）在吉尔伯特（Gilbert）和太平洋中部的吉尔伯特（Gilbert）和贾维斯群岛（Jarvis Islands）中，收集来自两个主要礁石建造物种的多个新的，中等长度（15 - 30年）的核心和分支。 （2）应用3-D CAT扫描和图像分析技术来量化每个物种，每个礁石部位的系统热阈值，恢复速率和弹性； （3）量化热和较低的菌落中的能量储备和共生基因型，建立钙化应力与死亡率风险之间的定量联系，并确定钙化对热应激的钙化反应的基础； （4）使用专门针对热带太平洋量身定制的OGCM，为目标珊瑚礁地点的近期气候变化产生动态一致的预测集； （5）将珊瑚数据与模型输出相结合，并在21世纪中太平洋岛屿组中的珊瑚中，在程度上加热的预计热应力预测。该项目包括通过WHOI的夏季学生奖学金计划为年轻的研究员，博士后调查员，研究生和几位本科研究人员提供资金。因为可以相对且廉价地应用量化热阈值和恢复速率的方法，以在大型空间尺度上生成许多不同珊瑚物种的数据，因此预期的成功结果将促进其他太平洋礁的相似数据收集。当与每周分辨的OGCM输出结合使用时，该数据“网络”将使21世纪热带太平洋的单个珊瑚礁的珊瑚反应对珊瑚反应的物种和深度的投影。所有研究将在国家和国际会议以及公共场所介绍；结果将在网站上汇总，并将由Co-Pis集成到本科和研究生课程中。