Collaborative Research: Dissolved organic matter feedbacks in coral reef resilience: The genomic & geochemical basis for microbial modulation of algal phase shifts

珊瑚礁退化，无论是由过度捕捞、营养污染、水质下降还是其他人为因素造成的，都与珊瑚礁向以肉质藻类为主的阶段转变有关。在许多情况下，管理和改善这些压力并不能使珊瑚恢复主导地位，珊瑚礁多年来一直处于藻类主导的状态。近十年的研究表明，增加藻类优势的轨迹正在重组微生物群落组成和代谢;研究人员假设微生物过程通过代谢藻类释放的有机化合物，从而通过缺氧和疾病对珊瑚施加压力，从而促进藻类优势的维持。珊瑚礁对这些阶段性变化的适应能力是珊瑚礁生态学中的一个关键问题，管理经历这些社区转变的珊瑚礁需要了解微生物相互作用在促进藻类过度生长和改变珊瑚礁生态系统功能方面的作用。这项研究将调查藻类产生的有机物，代谢有机物的微生物，以及这些过程对珊瑚健康和生长的影响。这项研究的影响，管理珊瑚礁弹性藻类相变测试的差异电阻珊瑚相关的微生物群落藻类和定义阈值的藻类物种覆盖改变生态系统的生物地球化学。该项目提供跨多个职业层次的指导，将代表性不足的本科生，两名研究生，一名博士后研究员以及一名初出茅庐的调查人员联系起来。该项目将整合溶解有机物（DOM）地球化学，微生物基因组学和生态系统过程的测量在生态相关的空间和时间尺度，以测试假设的机制，微生物介导的反馈可能会促进肉质藻类在太平洋珊瑚礁生态系统的传播。这项研究的一个关键成果将是了解珊瑚礁上的珊瑚和藻类的组成如何与复杂的微生物群落协同作用，以影响珊瑚礁生态系统对藻类相变的适应能力。新兴的分子和生物地球化学方法将被用来调查在多个空间和时间尺度上的微生物-DOM相互作用的机制。该项目将利用法属波利尼西亚莫奥雷亚珊瑚礁长期生态研究项目的背景环境数据、实验室设施和现场后勤资源，并为该计划调查珊瑚礁在全球变化中的恢复力的使命做出贡献。调查人员将量化DOM生产的批量昼夜模式，并表征发色组分的组成以及来自不同底栖藻类来源的游离和酸可水解中性单糖和氨基酸。该小组还将利用微生物遗传学和元转录组学，在现场控制的环境室中描述藻类DOM修正引起的浮游和珊瑚相关微生物群落分类组成和基因表达的变化，包括跟踪特定微生物谱系对藻类分泌物的利用。现场部署的100升帐篷围隔生态系统将被用来研究在现场昼夜模式耦合DOM的生产和消费，微生物群落基因组学和生态系统代谢的代表性底栖生物群落，包括藻类和珊瑚物种的组合。这些实验结果将共同指导解释的厘米尺度的空间动态的浮游生物和珊瑚相关的微生物基因组学和代谢的珊瑚-藻类相互作用的区域，包括边界层动态的氧气，细菌和DOM使用平面光电管，高通量流式细胞术和荧光光谱的实地调查。

Coral reef degradation, whether driven by overfishing, nutrient pollution, declining water quality, or other anthropogenic factors, is associated with a phase shift towards a reefs dominated by fleshy algae. In many cases managing and ameliorating these stressors does not lead to a return to coral dominance, and reefs languish in an algal-dominated state for years. Nearly a decade of research has demonstrated that trajectories toward increasing algal dominance are restructuring microbial community composition and metabolism; the investigators hypothesize that microbial processes facilitate the maintenance of algal dominance by metabolizing organic compounds released by algae thereby stressing corals through hypoxia and disease. The resilience of reefs to these phase shifts is a critical question in coral reef ecology, and managing reefs undergoing these community shifts requires developing an understanding of the role of microbial interactions in facilitating algal overgrowth and altering reef ecosystem function. The research proposed here will investigate the organics produced by algae, the microbes that metabolize the organics, and the impacts of these processes on coral health and growth. This research has implications for managing reef resilience to algal phase shifts by testing the differential resistance of coral-associated microbial communities to algae and defining thresholds of algal species cover which alter ecosystem biogeochemistry. This project provides mentoring across multiple career levels, linking underrepresented undergraduates, two graduate students, a postdoctoral researcher, and a beginning and established investigators. This project will integrate dissolved organic matter (DOM) geochemistry, microbial genomics and ecosystem process measurements at ecologically-relevant spatial and temporal scales to test hypothetical mechanisms by which microbially-mediated feedbacks may facilitate the spread of fleshy algae on Pacific reef ecosystems. A key product of this research will be understanding how the composition of corals and algae on reefs interact synergistically with complex microbial communities to influence reef ecosystem resilience to algal phase shifts. Emerging molecular and biogeochemical methods will be use to investigate mechanisms of microbial-DOM interactions at multiple spatial and temporal scales. This project will leverage the background environmental data, laboratory facilities and field logistical resources of the Mo'orea Coral Reef Long Term Ecological Research Project in French Polynesia and contribute to the mission of that program of investigating coral reef resilience in the face of global change. The investigators will quantify bulk diel patterns of DOM production and characterize the composition of chromophoric components and both free and acid-hydrolyzable neutral monosaccharides and amino acids from varying benthic algae sources. The team will also characterize planktonic and coral-associated microbial community changes in taxonomic composition and gene expression caused by algal DOM amendments in on-site controlled environmental chambers using phylogenetics and metatranscriptomics, including tracking algal exudate utilization by specific microbial lineages. Field-deployed 100 liter tent mesocosms will be used to examine in situ diel patterns of coupled DOM production and consumption, microbial community genomics and ecosystem metabolism over representative benthic communities comprising combinations of algal and coral species. Together these experimental results will guide interpretation of field surveys of centimeter-scale spatial dynamics of planktonic and coral-associated microbial genomics and metabolism at zones of coral-algal interaction, including boundary layer dynamics of oxygen, bacteria and DOM using planar optodes, high-throughput flow cytometry and fluorescence spectroscopy.