Collaborative Research: Ecological and biogeochemical role of Rhizaria in the oligotrophic ocean

根瘤菌是大型单细胞生物，对世界海洋的化学循环有贡献。普通根瘤菌（如棘虫、有孔虫、多胱氨酸、Phaeodarea）形成矿物壳，是海洋锶、二氧化硅和碳收支的一部分，它们至少占表层海洋生物碳库的5.2%。更好地了解现有的根瘤菌群、它们的生物量以及它们的种群如何在不同的海洋深度变化，对于模拟海洋营养循环至关重要，但对于地球上最大的生物群落之一、中央低营养海洋环流中的大型根瘤菌来说，这些信息解决得很差或缺乏。这个合作项目包括一个早期的职业团队和更成熟的研究人员，提供了开发根茎菌对深海下沉营养物质的贡献模型所需的测量，并增加了我们对营养物质如何在海洋中移动以及不断变化的环境条件如何影响这些循环的理解。它正在生成可供海洋学研究人员使用的大型数据集，并为本科生、研究生和高中生提供海洋学、生物学和数据科学主题的体验式学习机会。本研究提供了1)大大改进了对寡营养海洋中根瘤菌总生物量的估计；2)根瘤菌垂直分布和环境生态位特征的新测量方法；3)根瘤菌生物量和群落组成的季节变化测量方法；4)根瘤菌种群季节和空间变化的环境驱动因素识别；5)基于模型的根瘤菌对进入深海的垂直通量的贡献估计。研究人员正在结合使用Niskin瓶采样、颗粒凝胶捕集器、网束和根茎的尖端原位成像（使用水下视觉Profiler， UVP5-DEEP）来绕过其他采样方法的限制，以产生根茎生物量的准确估计。采样的深度范围很广（0-1200米），每隔一个月进行一次，并与作为百慕大大西洋时间序列研究（BATS）的一部分收集的大量其他海洋学测量数据相结合。UVP图像数据与根瘤菌分子鉴定相结合，使用群落元条形码、ZooSCAN成像和从网拖和凝胶捕集器收集的根瘤菌的条形码。研究人员正在使用根茎的特定大小元素分析和根茎生物量的季节性和垂直明确估计来模拟根茎对垂直通量的贡献。与百慕大大西洋时间序列和海洋通量计划收集的数据一起，有关根茎的新数据正在被纳入一个碳和营养物质向深海转移的模型中。该模型估计了根状菌可能影响碳循环的三种方式——以颗粒通量为食，为海洋雪提供压舱物，以及直接下沉——并显示了这些方式在空间和时间上的变化。该项目由生物海洋学、化学海洋学和促进竞争性研究（EPSCoR）计划共同资助。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。

Rhizaria are large, single-celled organisms that contribute to chemical cycles in the world’s oceans. Common Rhizaria (e.g. Acantharea, Foraminifera, Polycystines, Phaeodarea) form mineral shells that are part of the ocean’s strontium, silica, and carbon budgets, and they represent at least 5.2% of the oceanic biological carbon reservoir in the surface zone. Better understanding of groups of Rhizaria that are present, their biomass, and how their populations change across different ocean depths is essential to model oceanic nutrient cycles, but this information is poorly resolved or lacking for large Rhizaria in one of the largest biomes on Earth, the central, low-nutrient ocean gyres. This collaborative project involves a team of early career and more established investigators, provides measurements needed to develop a model of Rhizaria contribution to sinking nutrients in the deep ocean, and is adding to our understanding of how nutrients move in the oceans and how changing environmental conditions affect those cycles. It is generating large datasets that can be used by oceanographic researchers and is delivering oceanographic, biological, and data-science themed experiential learning opportunities for undergraduate, graduate, and high school students.This study provides 1) greatly improved estimates of total Rhizaria biomass in the oligotrophic ocean, 2) novel measurements of vertical distribution and environmental niche characteristics of Rhizaria, 3) measurements of seasonal variation in Rhizaria biomass and community composition, 4) identification of the environmental drivers of seasonal and spatial variation in Rhizaria populations, and 5) a model-based estimate of the contributions of Rhizaria to vertical flux into the deep ocean. The investigators are using a combination of Niskin bottle sampling, particle gel traps, net tows, and cutting-edge in situ imaging (using an Underwater Vision Profiler, UVP5-DEEP) of Rhizaria to bypass limitations in other sampling methods to produce accurate estimates of Rhizaria biomass. Sampling occurs across a wide depth range (0-1200 m), at monthly intervals, and in conjunction with a wide array of other oceanographic measurements collected as part of the Bermuda Atlantic Time-series Study (BATS). UVP imagery data is integrated with molecular identification of Rhizaria using community metabarcoding, ZooSCAN imaging, and barcoding of individual Rhizaria collected from net tows and gel traps taken in conjunction with UVP casts. The investigators are using size-specific elemental analyses of Rhizaria and seasonally and vertically explicit estimates of Rhizaria biomass to model Rhizaria contributions to vertical flux. Along with data collected by the Bermuda Atlantic Time Series and Ocean Flux Program, new data on Rhizaria are being incorporated into a model of carbon and nutrient transfer into the deep ocean. The model estimates three ways that Rhizaria likely impact the carbon cycle -- by feeding on particle flux, by contributing ballast to marine snow, and by sinking directly -- and shows how these might vary across space and time. This project is jointly funded by the Biological Oceanography, Chemical Oceanography, and Established Program to Stimulate Competitive Research (EPSCoR) 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.