Collaborative Research: Physiology and Biogeochemistry of Repeatedly Bleached and Recovering Caribbean Corals

全球珊瑚礁的整体稳定性和健康状况正在以前所未有的速度下降。大量珊瑚白化，暴露在高温下导致大量内共生鞭毛藻（共生菌属，通常称为虫黄藻）和/或光合色素的损失，是这种共生关系是多么脆弱的一个主要全球例子。虽然我们已经开始了解白化对生态和生理的影响，但在知识方面仍然存在关键的基本差距。特别是，越来越清楚的是，a)并非所有珊瑚都以同样的方式对白化事件作出反应或从白化事件中恢复过来，b)每年或反复发生的白化事件对珊瑚的影响尚未得到足够详细的研究。几种不相互排斥的生态和生理途径可能影响特定珊瑚物种如何屈服于白化或从白化中恢复。最近的证据表明，面对未来海水变暖和大规模白化事件，以下特征可能对珊瑚的生存起关键作用：1)营养分配的转变（例如，对自养和异养的比例依赖）和能量储备利用；2)通过宿主和藻类介导的生理反应增强热耐受性；3)不同共生物种的庇护。然而，这些机制尚未在覆盖整个珊瑚全息生物系统（藻类，宿主组织和骨架）的统一方法中进行研究，或者在重复漂白的情况下进行研究。本研究的总体目标如下：1)确定单次和重复漂白对某些加勒比珊瑚物种的生理、生物地球化学和恢复的影响；2)确定哪种共生类型和宿主物种组合对单次和重复漂白更有弹性，它们的生理和生物地球化学的哪些方面使它们具有弹性，并利用这些信息来评估加勒比珊瑚礁的长期持久性。为了实现这些目标，将测量以下生理变量：1)共生菌类型，光化学功能和藻类应激生理；2)动物宿主能量储备，防御酶浓度，骨骼生长和摄食能力在Porites Porites Porites astreoides和Montastraea faveolata中。在模拟自然白化的热应力下，我们会立即对珊瑚进行检查，并在短期和长期时间尺度上监测珊瑚的恢复情况。接下来，将在接下来的一年检查重复漂白的影响，然后在下一个恢复期进行检查。本研究旨在同时评估共生藻类、珊瑚宿主和骨骼，并确定每种共生类型和宿主物种组合的生理反应和恢复模式，这将表明加勒比珊瑚对未来更频繁的热扰动的恢复能力。这项研究的结果将大大增加对珊瑚礁珊瑚如何（或是否）在未来气候变化中生存的理解。这对加勒比海的珊瑚来说尤其重要，因为那里的敏感性似乎非常低，而且预计在未来20-30年内，那里的白化将每两年发生一次。这些信息是未来有效管理珊瑚礁的关键。该项目将包括两名博士生和几名本科生的培训，pi将把研究成果融入到他们的教学中。几名女性和西班牙裔学生（都是海洋科学领域的少数民族）由私人顾问指导。此外，格罗托利和华纳之间的合作还将通过设在小开曼研究中心的加勒比中部海洋研究所的实地研究监测工作，以及美国国家海洋和大气管理局珊瑚礁观察项目的同事们提供的基于遥感的产品得到加强。研究结果将通过同行评议的出版物、在科学会议上的报告以及通过PI各自的网站在网上广泛传播。

The overall stability and health of coral reefs is declining world-wide at an unprecedented rate. Mass coral bleaching, wherein exposure to elevated temperature leads to the loss of significant numbers of endosymbiotic dinoflagellates (Symbiodinium spp., commonly called zooxanthellae) and/or photosynthetic pigments, serves as a primary global example of how fragile this symbiosis is. While we have begun to understand the ecological and physiological impacts of bleaching, there remain key fundamental gaps in knowledge. In particular, it is becoming increasingly clear that a) not all corals either respond to, or recover from, bleaching events the same way, and that b) the impact of annual or repeated bleaching events on corals has not been examined in sufficient detail. Several non-mutually exclusive ecological and physiological pathways could impact how a particular coral species succumbs to or recovers from bleaching. Recent evidence suggests that the following features may play key roles for coral survival in the face of future seawater warming and mass bleaching events: 1) shifts in trophic partitioning (e.g., proportional reliance on autotrophy and heterotrophy) and energy reserve utilization, 2) enhanced thermal tolerance through host and algal-mediated physiological responses, and 3) harboring of different Symbiodinium phylotypes. However, these mechanisms have yet to be investigated in a unified approach that covers the entire coral holobiont system (algae, host tissue, and skeleton), or under scenarios of repeated bleaching.The overall objectives of this study are as follows: 1) to determine the effect of single and repeated bleaching on the physiology, biogeochemistry, and recovery of some Caribbean coral species, and 2) to determine which Symbiodinium-type and host-species combinations are more resilient to single and repeated bleaching, what aspects of their physiology and biogeochemistry render them resilient, and to use this information to evaluate the long-term persistence of Caribbean coral reefs. To address these objectives, the following physiological variables will be measured: 1) Symbiodinium type, photochemical function and algal stress physiology, and 2) animal host energy reserves, defense enzyme concentration, skeletal growth, and feeding capacity in the corals Porites porites, Porites astreoides, and Montastraea faveolata. Corals will be examined immediately following thermal stress designed to approximate natural bleaching, and recovery will be monitored over short and long-term time scales. Next, the impact of repeated bleaching will be examined in the subsequent year, followed by examination over the next recovery period. This research is designed to simultaneously evaluate the symbiotic algae, coral host, and skeleton, and to identify patterns of physiological responses and recovery of each Symbiodinium-type and host-species combination that would be indicative of the resilience capacity of Caribbean corals to future more frequent thermal perturbations.The results of this research should significantly increase understanding of how (or if) reef corals can survive future climate change. This is especially critical for Caribbean corals where sensitivity appears to have a very low threshold, and where bleaching is predicted to occur biannually within the next 20-30 years. Such information is key for the effective future management of coral reefs. This project will incorporate the training of two PhD students and several undergraduates, and the PIs will incorporate the research findings into their teaching. Several female and Hispanic students (both minorities in marine sciences) are mentored by the PIs. In addition, collaborative efforts between Grottoli and Warner will be enhanced by the field research monitoring efforts of the Central Caribbean Marine Institute at the Little Cayman Research Center, and the remote-sensing-based products from colleagues at the NOAA Coral Reef Watch Program. Results of the research will be broadly disseminated through peer reviewed publications, presentations at scientific conferences, and online via the PI's respective websites.