Can Coral Reefs in the Central Pacific Survive Ocean Warming? A 2015 El Nino Test

该项目支持在一次特别强烈的厄尔尼诺事件期间对热带太平洋中部中心进行为期7天的探险，这可以说是有记录以来最强的事件之一。目标是位于凉爽、营养丰富的赤道暗流(EUC)路径上的贾维斯岛。由于其地理位置，贾维斯是一个原始的、无人居住的珊瑚礁生态系统，其特点是生产力提高，大型捕食性鱼类、海龟、珊瑚和其他海洋生物密度高。然而，由于厄尔尼诺现象，贾维斯的海面温度目前比每年这个时候的正常水平高出3.9摄氏度。这为研究人员提供了一个独特的机会，来研究高生产力的珊瑚礁生态系统如何对海洋变暖做出反应，以及恢复的机制和时间尺度。信息将通过在珊瑚礁上部署最先进的仪器，以及从表面到150米深的海水、颗粒物、浮游生物和珊瑚采样来收集。这将是第一次在漂白活动期间前往贾维斯岛的探险。美国太平洋偏远岛屿海洋国家纪念碑(PRIMNM)最近扩大，作为多国承诺的一部分，为子孙后代保护和保存我们的大片海洋和海洋资源。然而，这些保护措施并不能保护海洋生态系统免受21世纪气候变化的影响。该项目调查赤道海洋环流同时发生变化的可能性，以减轻全球变暖对赤道礁的影响。它测试了一些假设，这些假设改善了对珊瑚礁对气候变化适应能力的基本机制的理解，以及确定将此类珊瑚礁系统纳入保护区网络的能力。该游轮支持四名博士生的培训，其中三名是国家科学基金/国防科学与工程研究生研究员，并提供支持六篇博士论文的材料。成果将在国际会议和研讨会上分享，并发表在同行评议的期刊上。从邮轮收集和产生的所有数据将通过生物和化学海洋学数据管理办公室公开。全球气候模型预测，本世纪热带太平洋中部变暖加剧。这意味着，在最近扩大的PRIMNM范围内，七个珊瑚礁生态系统中有五个正在沐浴的水域将变暖超过3摄氏度。这种变暖的速度远远超过了造礁珊瑚的已知热容忍度，这加剧了人们对这些珊瑚礁可能无法在21世纪气候变化中幸存下来的担忧。然而，同样的模型预测了EUC的同时加强，这一预测得到了观测的支持。EUC携带着赤道岛屿西侧上升的凉爽、营养丰富的水域，冷却了珊瑚礁，提高了当地的生产力。如果GCM的预测成为现实，一个加强的EUC可以通过降低变暖的速度和支持在白化中幸存下来的充满活力的珊瑚群落来调节海洋变暖对这些珊瑚礁的影响。这一提议利用热带太平洋当前的厄尔尼诺状态来检验以下假设：(1)珊瑚群落在每次厄尔尼诺期间沐浴在营养丰富、多产的赤道中太平洋水域漂白，但死亡率很低，因此活着覆盖率仍然很高。(2)局部EUC增强的生产力支持营养丰富的珊瑚群落，这些群落代谢现有的脂肪储备，以支持漂白过程中的能量需求。(3)此外，赤道珊瑚采用灵活的摄食策略，从富氮(大于5微摩尔硝酸盐)的拉尼娜条件下的直接硝酸盐摄取转变为在氮“差”(小于3微摩尔硝酸盐)的厄尔尼诺条件下的异养摄食。我们认为，在外源的推动下，赤道太平洋珊瑚群落在白化中存活下来，死亡率有限，珊瑚覆盖率保持在较高水平，珊瑚生长速度迅速恢复。如果该项目产生的数据支持我们的假设，那么海洋保护和政治保护相结合可能会使珊瑚礁在21世纪的生存潜力最大化。

This project supports a 7 day expedition to the heart of the central tropical Pacific during a particularly strong El Niño event, arguably one of the strongest on record. The target is Jarvis Island, located in the path of the cool, nutrient-rich Equatorial Under-Current (EUC). As a consequence of its location, Jarvis, a pristine, uninhabited coral reef ecosystem, is characterized by enhanced productivity, high densities of large predatory fish, turtles, corals and other sea life. However, sea surface temperatures on Jarvis are currently 3.9 degrees Celsius higher than normal for this time of year, due to El Niño. This provides investigators with a unique opportunity to examine how a highly productive reef ecosystem responds to ocean warming, and the mechanisms and timescales for recovery. Information will be collected by deploying state-of-the-art instrumentation on the reef, and sampling seawater, particulates, plankton and corals from surface to 150 meters depth. This will be the first expedition to Jarvis Island during a bleaching event. The US Pacific Remote Island Marine National Monument (PRIMNM) was recently expanded as part of a multi-national commitment to protect and preserve vast areas of our ocean and ocean resources for future generations. However, these protections do not shield ocean ecosystems from the impacts of 21st century climate change. The project investigates the potential for simultaneous changes in equatorial ocean circulation to lessen the impacts of the global warming for equatorial reefs. It tests hypotheses that improve understanding of fundamental mechanisms of coral reef resilience to climate change, and the ability to identify such reef systems for inclusion in Protected Area Networks. The cruise supports the training of four PhD students, three of whom are National Science Foundation / National Defense Science and Engineering graduate research fellows, and provide material in support of six PhD theses. Results will be shared at international meetings and workshops, and published in peer-reviewed journals. All data collected and generated from the cruise will be made publicly available via the Biological and Chemical Oceanography Data Management Office.Global climate models project enhanced warming of the central tropical Pacific over this century. By implication, waters bathing five out of the seven coral reef ecosystems protected within the recently expanded PRIMNM, will warm by more than 3 degrees Celsius. This rate of warming far exceeds the known thermal tolerances of reef-building corals, fueling concerns that these reefs may not survive 21st century climate change. However the same models project a concurrent strengthening of the EUC, a projection supported by observations. The EUC carries cool, nutrient-rich waters that upwell on the west sides of the equatorial islands, cooling the reefs and enhancing productivity locally. If the GCM projections are realized, a strengthening EUC could modulate the impact of ocean warming for these reefs by reducing the rate of warming and supporting energetically replete coral communities that survive bleaching. This proposal exploits the current El Niño state of the tropical Pacific to test the following hypotheses: (1) Coral communities bathed in the nutrient-rich, productive waters of the central equatorial Pacific bleach during every El Niño, but mortality is low and as a result, percent live cover remains high. (2) Localized EUC-enhanced productivity supports nutritionally replete coral communities, which metabolize existing lipid reserves to support energetic requirements during bleaching. (3) In addition, equatorial corals adopt a flexible feeding strategy, switching from direct nitrate uptake during nitrogen-rich (greater than 5 micromolar nitrate) La Niña conditions to heterotrophic feeding during nitrogen-"poor" (less than 3 micromolar nitrate) El Niño conditions. We propose that, fueled by exogenous sources, equatorial Pacific coral communities survive bleaching with limited mortality, coral cover remains high and coral growth rates quickly recover. If data generated under this project support our hypotheses, then the combination of oceanographic and political protections could maximize the potential for coral reef survival through the 21st century.