Collaborative Research: The physiology and ecology of widespread 'stress tolerant' coral endosymbionts: coral 'saviors' or opportunistic invaders?

海洋变暖正以多种方式影响着地球上的生命。高温会破坏鞭毛藻（共生藻）和造礁珊瑚之间的内共生关系（即珊瑚白化），从而有可能在全球范围内丧失一个重要的海洋生态系统。珊瑚-鞭毛藻共生生物对全球气候变化带来的环境胁迫的生理、生态和进化反应是复杂的。某些类型的共生藻类的传播可能会增加珊瑚的热应力耐受性，并帮助它们在温暖的海洋中生存，但可能不是没有珊瑚健康的权衡。这种暂时被命名为共生菌的鞭毛藻在整个加勒比地区的许多珊瑚中越来越常见，但相对于其他共生体，它的丰度通常较低。虽然在变暖期间和变暖之后，南沟菌的数量会增加，但在恢复正常条件后，它往往会被其他共生体所取代。遗传证据表明，S. trenchi最近入侵和/或扩展到加勒比地区，并与许多似乎优化不良或适应不良的珊瑚发展了联系，相对于它与印度太平洋地区的珊瑚维持的共生关系。该项目将研究大西洋和太平洋珊瑚中S. trenchi的共生生态学和生理学。漂白实验将检查温度升高对藻类向宿主珊瑚转移碳的影响（通过稳定同位素标记），以及与其他共生菌相比，trenchi菌落的光合作用和生长情况。将研究共生群落转移的可能性，以及基于漂白严重程度和恢复时间的长期菌落生长的改变。互惠移植研究将检查太平洋珊瑚之间的竞争相互作用和共生体的稳定性。这些研究将测试S. trenchi的持续传播是否会影响加勒比地区的珊瑚生长，以及如果环境条件恶化，它是否会在印度-太平洋地区产生类似的影响。该项目的结果有可能提供关于广泛分布的共生藻类物种如何（或是否）影响造礁珊瑚的恢复能力以及它们在气候变化导致的海洋变暖中生存的潜力的变革性信息。除了培养一名博士后学者和几名研究生外，该项目还将通过与帕劳国家水族馆、帕劳国际珊瑚礁中心和当地学校的几次外展努力，加强科学发现和弱势群体的参与。将同几名当地高中教师和学生一起发展海洋共生和科学的教育单位，并将向帕劳社区学院的学生提供独特的研究机会。同样，一个新的教育性展览将在特拉华大学的“海岸日”开放日上展出，展示全球气候如何影响珊瑚礁，并描述当前的研究，以更好地理解珊瑚-藻类共生的生理学。展品随后将捐赠给帕劳水族馆供将来使用。该奖项由美国国家科学基金会国际和综合活动办公室共同资助。

Ocean warming is affecting life on our planet in many ways. High temperature can disrupt the endosymbioses between dinoflagellate algae (Symbiodinium spp.) and reef-building corals (i.e. coral bleaching), thereby risking the global loss of a critical marine ecosystem. The physiological, ecological and evolutionary responses of coral-dinoflagellate symbioses to environmental stress brought on by global climate change are complex. The spread of certain types of symbiotic algae may increase the thermal stress tolerance among corals and help them persist in warmer oceans, but perhaps not without trade-offs to the health of the coral. The dinoflagellate tentatively named Symbiodinium trenchi has become increasingly more common in numerous corals throughout the Caribbean, but is often at low-abundance relative to other symbionts. While S. trenchi can increase in abundance during and after warming, it is often displaced by other symbionts following a return to normal conditions. Genetic evidence indicates that S. trenchi recently invaded and/or expanded in the Caribbean and has developed associations with many corals that seem to be poorly optimized, or mal-adapted, relative to the symbioses it maintains with corals in the Indo-Pacific. This project will investigate the symbiosis ecology and physiology of S. trenchi in corals from the Atlantic and Pacific Oceans. Bleaching experiments will examine the effects of increased temperature on transfer of carbon from the algae to the host coral (via stable isotopic tagging), as well as photosynthesis and growth among colonies harboring S. trenchi compared to colonies harboring other Symbiodinium spp. The potential for symbiont community shifts as well as altered long-term colony growth based on bleaching severity and recovery time will be investigated. A reciprocal transplant study will examine the competitive interaction and stability of symbionts among Pacific corals. These studies will test if the continued spread of S. trenchi will affect coral growth in the Caribbean and whether it might behave similarly in the Indo-Pacific if environmental conditions worsen. The results from this project have the potential to supply transformative information regarding how (or if) a widely distributed symbiotic algal species may influence the resilience of reef-building corals and their potential to survive projected increases in ocean warming due to climate change. In addition to training one postdoctoral scholar and several graduate students, this project will enhance scientific discovery and participation of underrepresented groups via several outreach efforts with the Palau National Aquarium, Palau International Coral Reef Center, and local schools. Educational units in marine symbioses and science will be developed with several local high school teachers and students, and unique research opportunities will be provided to students at the Palau Community College. Likewise, a new educational display addressing how global climate may impact coral reefs, and describing the current research to better understand the physiology of coral-algal symbioses, will be developed and presented at the University of Delaware open house "Coast Day." The display will be donated subsequently to the Palau Aquarium for future use.This award is co-funded by NSF's Office of International and Integrative Activities.