CAREER: Helping or hindering? Determining the influence of repetitive marine heatwaves on acclimatization of reef-building corals across biological scales

气候变化导致的海洋变暖导致世界各地珊瑚礁的惊人损失，现在是威胁珊瑚礁生态系统生存的最紧迫的压力因素之一。随着与海洋变暖相关的海洋热浪变得越来越频繁，迫切需要了解造礁珊瑚是否以及如何能够应对这些重复的压力事件，从而在快速变暖的海洋中生存。为了解决这个问题，该项目正在调查珊瑚礁上的珊瑚如何应对反复出现的海洋热浪，以确定反复暴露于热应激是否会通过适应提高珊瑚对更高温度的耐受性，还是会导致压力的积累，从而降低未来压力后的性能和存活率。这项研究的结果对于了解当前这一代珊瑚将如何应对日益变暖的海洋，以及适应环境是否会为足够多的个体赢得足够的时间来适应并促进珊瑚在未来的持久性至关重要。此外，该项目还通过全球变化生物学和生态学方面的高级博士后培养中学生。具体来说，研究人员正在增加本科生的研究机会，通过在全球海洋变化生物学中开发一种新的实践性课程本科生研究经验（CURE），每年将惠及数百名学生。此外，还在开展外展工作，以增加历史上被剥夺海洋科学权利的学生的参与和保留，包括为即将入学的第一代低收入本科生创建动手珊瑚礁和气候变化活动，以及一个专业发展项目，培训初中和高中教师在费城公立学区的课堂上开展这些气候变化活动。该校主要招收低收入的黑人和拉丁裔学生。暴露于亚致死热应激后的适应可能是珊瑚在气候变化中生存的重要保护机制。然而，海洋热浪的环境记忆在驱动适应环境中的作用，或者相反，对造礁珊瑚的应力积累和敏感化的作用还不是很清楚。本研究利用原位和中生态实验的结合来解决这个问题，以评估反复热浪对具有不同漂白历史的珊瑚的细胞，有机体和生态后果。具体来说，研究人员正在监测夏威夷的两种造礁珊瑚物种，Montipora capitata和Porites compressa，它们对白化敏感和抗白化的相邻同种个体。这些珊瑚已经通过多次漂白事件进行了超过7年的监测，并被用于测试海洋热浪的环境记忆由于物种内部和物种之间适应能力的表型差异而差异地改变珊瑚热性能的假设。这项工作旨在确定具有不同漂白历史的珊瑚的漂白阈值是否随时间而变化，并利用底栖生物调查、摄影测量和原位生长测量相结合的方法评估这些表型对珊瑚钙化、生存和种群大小结构的影响。利用热性能曲线评估热浪对珊瑚生理的环境记忆的影响，以确定呼吸、光合作用、钙化和宿主细胞内pH值的热最佳值如何随时间变化（例如环境年与热浪年），以及这种反应在具有不同漂白表型的珊瑚之间是否不同。最后，通过将珊瑚暴露在实验中不断升高的温度中，评估了藻类内共生体对适应环境的贡献，潜在地揭示了高保真（P. compressa）和世界性（M. capitata）共生体关联的珊瑚对宿主和共生体特征的适应程度或敏化程度的差异。通过了解生物尺度上热性能的表型多样性，本研究改进了面对持续气候危机时珊瑚持久性的预测。本项目由生物海洋学、综合生态生理学和海洋教育计划资助。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Ocean warming driven by climate change has led to staggering losses of coral on reefs worldwide and is now among the most pressing of stressors threatening the survival of coral reef ecosystems today. As marine heatwaves associated with ocean warming become increasingly frequent, it is urgent to understand if and how reef-building corals will be able to respond to these repeat stress events and thus survive in a rapidly warming ocean. To address this problem, this project is investigating how corals on the reef respond to recurring marine heatwaves in order to identify if repeat exposure to heat stress promotes coral tolerance of higher temperatures via acclimatization or instead leads to the accumulation of stress and thus reduced performance and survival following future stress. The results of this study are critical for understanding how the current generation of corals will respond to increasingly warmer oceans, and whether acclimatization will buy enough individuals sufficient time for adaptation to occur and promote coral persistence into the future. In addition, this project is training students from secondary schools through advanced postdoctoral researchers in global change biology and ecology. Specifically, the investigators are increasing access to research opportunities for undergraduate students by developing a new hands-on course-based undergraduate research experience (CURE) in Global Ocean Change Biology that will reach hundreds of students per year. Outreach efforts are also being developed to increase the participation and retention of historically disenfranchised students in marine science, and include creation of hands-on coral reefs and climate change activities for incoming first-generation, low-income undergraduate students and a professional development program to train middle and high-school teachers to deploy these climate change activities in their classrooms in the Philadelphia Public School District, which serves a predominantly low-income Black and Latinx student body. Acclimatization following exposure to sub-lethal heat stress may be an important protective mechanism for corals to survive a changing climate. However, the role of environmental memory of marine heatwaves in driving acclimatization or, conversely, stress accumulation and sensitization of reef-building corals is not well understood. This study is addressing this question using a combination of in situ and mesocosm experiments to assess the cellular, organismal, and ecological consequences of repeat heatwaves on corals with contrasting bleaching histories. Specifically, the researchers are monitoring adjacent conspecific pairs of bleaching-susceptible and bleaching-resistant individuals of two reef-building coral species in Hawaii, Montipora capitata and Porites compressa. These corals have been monitored for over 7 years through multiple bleaching events and are being used to test the hypothesis that environmental memory of marine heatwaves differentially alters coral thermal performance due to phenotypic variation in acclimatization ability within and between species. This work is identifying whether the bleaching thresholds of corals with different bleaching histories varies through time, and the consequences of these phenotypes on coral calcification, survival, and population size structure are being assessed using a combination of benthic surveys, photogrammetry, and in situ growth measurements. The influence of environmental memory of heatwaves on coral physiology is being assessed using thermal performance curves to determine how the thermal optima of respiration, photosynthesis, calcification, and host intracellular pH change (or not) over time (e.g. ambient vs. heatwave years) and if that response differs between corals with contrasting bleaching phenotypes. Finally, the contribution of algal endosymbionts to acclimatization is being evaluated by exposing corals to a range of increasing temperatures in experimental mesocosms, potentially uncovering differences in the degree of acclimatization or sensitization for host vs. symbiont traits in corals with high fidelity (P. compressa) vs. cosmopolitan (M. capitata) symbiont associations. By understanding of the phenotypic diversity in thermal performance across biological scales, this research improves predictions of coral persistence in the face of the ongoing climate crisis.This project is supported by the Biological Oceanography, Integrative Ecological Physiology, and Ocean Education Programs.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.