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

珊瑚礁的整体稳定性和健康状况正在以前所未有的速度在全世界范围内下降。大规模珊瑚漂白，其中暴露于高温导致大量的内共生甲藻（Symbiodinium spp.，通常称为虫黄藻）和/或光合色素，作为这种共生关系是多么脆弱的主要全球性例子。虽然我们已经开始了解漂白的生态和生理影响，但在知识方面仍然存在关键的根本差距。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漂白事件作出反应或从漂白事件中恢复过来，B）每年或重复的漂白事件对珊瑚的影响尚未得到足够详细的研究。若干互不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漂白或从漂白中恢复。最近的证据表明，面对未来的海水变暖和大规模漂白事件，以下特征可能对珊瑚的生存起关键作用：1）营养分区的变化（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耐热性，和3）窝藏不同的共生甲藻类型。然而，这些机制还有待于在一个统一的方法，涵盖整个珊瑚holobiont系统进行调查（藻类、宿主组织和骨骼），或在反复漂白的情况下。本研究的总体目标如下：1）确定单一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，和2）以确定哪些共生藻型和宿主物种的组合是更有弹性的单一和重复漂白，他们的生理和生物地球化学的哪些方面使他们恢复，并使用这一信息来评估加勒比珊瑚礁的长期持久性。为了解决这些目标，将测量以下生理变量：1）共生藻类型、光化学功能和藻类应激生理学，以及2）动物宿主能量储备、防御酶浓度、骨骼生长和珊瑚Porites porites、Porites astreoides和Montastraea faveolata中的摄食能力。珊瑚将在接近自然漂白的热应力后立即进行检查，并将在短期和长期时间范围内监测恢复情况。接下来，将在下一年检查重复漂白的影响，然后在下一个恢复期进行检查。这项研究旨在同时评估共生藻类，珊瑚宿主和骨骼，并确定每种共生藻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。珊瑚礁可以在未来的气候变化中生存下来。这对加勒比海珊瑚尤其重要，因为那里的敏感性似乎很低，预计在今后20-30年内，那里的漂白现象将每两年发生一次。这些信息是今后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，而PI将把研究结果纳入他们的教学中。一些女性和西班牙裔学生（都是海洋科学的少数民族）由PI指导。此外，Grottoli和Warner之间的合作努力将通过小开曼岛研究中心的中加勒比海洋研究所的实地研究监测工作以及NOAA珊瑚礁观察方案同事的遥感产品得到加强。研究结果将通过同行评审的出版物、在科学会议上的演讲以及通过PI各自的网站在线广泛传播。

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.