Collaborative Research: Diel dynamics of dissolved organic matter production and remineralization as a driver of coral reef nutrient recycling

该项目发展了对珊瑚礁生态系统中生物微生物生态学和生物地球化学的核心理解。它阐述了至关重要的营养循环过程如何在珊瑚覆盖和养分可获得性的不同梯度上有所不同，这两个因素被强调为人类世珊瑚礁衰退的主要驱动因素，这使得研究结果对寻求加强基于生态系统的珊瑚礁恢复方法的管理者有用。研究人员正在莫雷亚长期生态研究基地(MCR-LTER)收集莫雷亚周围珊瑚礁微生物和生物地球化学过程的Diel测量数据。他们正在使用已建立的海底覆盖的空间梯度，从珊瑚到大型藻类的优势，以及营养输入。总体而言，这项研究提高了我们对这些关键环境因素如何影响DIEL微生物-DOM相互作用和养分循环的理解。在莫雷亚观察到的持续的大型藻类相移被假设与营养物质污染有关，这项工作直接让人们了解这些变化如何影响莫雷亚珊瑚礁的营养循环。培养几名本科生和两名研究生，一名生物学，一名海洋学，由两所少数民族服务的高等教育机构分担。该项目还支持与海洋探索研究所的积极外联计划，重点是让圣地亚哥面向海洋的高中生参与到面向海洋的职业生涯中，以及与密歇根大学的海洋赠款计划，以支持夏威夷当地的珊瑚礁弹性倡议。珊瑚礁展示了任何生态系统类型中初级生产力和分解率最高的一些项目，但在地球上一些营养最少的水域仍然存在，这意味着通过有机物质严格循环大量营养素。过去半个世纪在珊瑚礁生物地球化学方面的工作突出表明，这种细菌分解有机物是维持营养物质保持和珊瑚礁生产力的一种可能机制。该项目应用现代元基因组学和非靶向代谢组学来测试明确定义的假设，即Diel微生物-DOM相互作用如何推动营养物质在珊瑚礁中的循环和保留。研究人员首次解决了有机和无机C、N和P的现场耦合动态(使用大宗元素和光谱方法)、微生物丰度和种群结构(使用DNA测序和流式细胞仪)以及多个珊瑚礁栖息地中DOM的化学成分(使用非靶向串联质谱仪)，跨越底栖生物覆盖和营养可获得性的梯度。这些模式为第二次原位Diel采样活动提供了信息，以解决代谢途径(使用元基因组学)、外源酶活性(使用转录组学和酶分析)和特定代谢物的转化(通过分子网络跟踪)的动态耦合，以提取在营养循环中发挥作用的微生物有机物分解的共同机制。该项目是在Moorea珊瑚礁长期生态研究计划内进行的，利用了关于多个珊瑚礁栖息地的丰富的时间序列数据，并将我们的现场采样与正在进行的物理、地球化学和生物监测计划联系起来。通过将尖端的分子方法与田野生态学和微生物海洋学中成熟的技术相结合，这项研究计划确定了营养物质分解和再矿化过程中的关键微生物和分子参与者，长期以来一直被认为是维持健康珊瑚礁的核心。该奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

This project develops a core understanding of diel microbial ecology and biogeochemistry in coral reef ecosystems. It contextualizes how crucial nutrient recycling processes vary across gradients of coral cover and nutrient availability, two factors highlighted as the main drivers of reef decline in the Anthropocene, making the results useful to managers seeking to enhance ecosystem-based approaches to reef restoration. The investigators are collecting diel measurements of microbial and biogeochemical processes at coral reefs around Mo’orea at the Long Term Ecological Research site there (MCR-LTER). They are using established spatial gradients of benthic cover, from coral to macroalgal dominance, and nutrient inputs. Overall the research improves our understanding of how these key environmental factors influence diel microbe-DOM interactions and nutrient recycling. The ongoing macroalgal phase shifts observed at Mo’orea are hypothesized to be related to nutrient pollution, and this work directly informs understanding of how these changes are impacting nutrient cycling in the reefs of Mo’orea. The training of several undergraduate students and two graduate students, one in Biology and one in Oceanography is shared between two minority serving institutions of higher education. The project also supports active outreach programs with the Ocean Discovery Institute focused on engaging underrepresented high school students in ocean-oriented careers in San Diego, and with the UH College Sea Grant Program to support coral reef resilience initiatives locally in Hawai‘i.Coral reefs exhibit some of the highest rates of primary production and decomposition of any ecosystem type yet persist in some of the most oligotrophic waters on the planet, implying tight recycling of macronutrients through organic matter. The last half century of work on the biogeochemistry of reefs have highlighted this bacterial decomposition of organic matter as a likely mechanism for maintaining nutrient retention and reef productivity. This project applies modern metagenomics and untargeted metabolomics to test clearly defined hypotheses of how diel microbe-DOM interactions drive nutrient recycling and retention in reefs. The investigators are first resolving coupled in situ diel dynamics of organic and inorganic C, N and P (using bulk elemental and spectroscopic methods), microbial abundances and population structures (using DNA sequencing and flow cytometry) and the chemical composition of DOM (using untargeted tandem mass spectrometry) in multiple reef habitats across a gradient of benthic cover and nutrient availability. These patterns inform the second in situ diel sampling campaign resolving the dynamic coupling of metabolic pathways (using metagenomics), exoenzymatic activity (using transcriptomics and enzyme assays) and transformations of specific metabolites (tracked via molecular networking) to distill common mechanisms of microbial organic matter decomposition that play a role in nutrient cycling. This project is being conducted within the Moorea Coral Reef Long Term Ecological Research program, leveraging a wealth of time series data on multiple reef habitats as well as contextualizing our in situ sampling with ongoing physical, geochemical and biological monitoring programs. By integrating cutting edge molecular approaches with well-established techniques in field ecology and microbial oceanography, this research program identifies key microbial and molecular players in the nutrient decomposition and remineralization processes long hypothesized to be central to maintaining healthy reefs.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.