Collaborative Research: Mesoscale variability in nitrogen sources and food-web dynamics supporting larval southern bluefin tuna in the eastern Indian Ocean

合作研究：支持东印度洋南部蓝鳍金枪鱼幼体的氮源和食物网动态的中尺度变化

• 批准号: 1851381
• 负责人: Karen Selph
• 金额: $ 11.71万
• 依托单位: University of Hawaii
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2019
• 资助国家: 美国
• 起止时间: 2019-09-01 至 2023-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1851381&HistoricalAwards=false
• 关键词: Collaborative; Research; Mesoscale; variability; nitrogen

The small area between NW Australia and Indonesia in the eastern Indian Ocean (IO) is the only known spawning ground of Southern Bluefin Tuna (SBT), a critically endangered top marine predator. Adult SBT migrate thousands of miles each year from high latitude feeding areas to lay their eggs in these tropical waters, where food concentrations on average are below levels that can support optimal feeding and growth of their larvae. Many critical aspects of this habitat are poorly known, such as the main source of nitrogen nutrient that sustains system productivity, how the planktonic food web operates to produce the unusual types of zooplankton prey that tuna larvae prefer, and how environmental differences in habitat quality associated with ocean fronts and eddies might be utilized by adult spawning tuna to give their larvae a greater chance for rapid growth and survival success. This project investigates these questions on a 38-day expedition in early 2021, during the peak time of SBT spawning. This project is a US contribution to the 2nd International Indian Ocean Expedition (IIOE-2) that advances understanding of biogeochemical and ecological dynamics in the poorly studied eastern IO. This is the first detailed study of nitrogen and carbon cycling in the region linking Pacific and IO waters. The shared dietary preferences of SBT larvae with those of other large tuna and billfish species may also make the insights gained broadly applicable to understanding larval recruitment issues for top consumers in other marine ecosystems. New information from the study will enhance international management efforts for SBT. The shared larval dietary preferences of large tuna and billfish species may also extend the insights gained broadly to many other marine top consumers, including Atlantic bluefin tuna that spawn in US waters of the Gulf of Mexico. The end-to-end study approach, highlights connections among physical environmental variability, biogeochemistry, and plankton food webs leading to charismatic and economically valuable fish production, is the theme for developing educational tools and modules through the ?scientists-in-the-schools? program of the Center for Ocean-Atmospheric Prediction Studies at Florida State University, through a program for enhancing STEM learning pathways for underrepresented students in Hawaii, and through public outreach products for display at the Birch Aquarium in San Diego. The study also aims to support an immersive field experience to introduce talented high school students to marine research, with the goal of developing a sustainable marine-related educational program for underrepresented students in rural northwestern Florida.Southern Bluefin Tuna (SBT) migrate long distances from high-latitude feeding grounds to spawn exclusively in a small oligotrophic area of the tropical eastern Indian Ocean (IO) that is rich in mesoscale structures, driven by complex currents and seasonally reversing monsoonal winds. To survive, SBT larvae must feed and grow rapidly under environmental conditions that challenge conventional understanding of food-web structure and functional relationships in poor open-ocean systems. The preferred prey of SBT larvae, cladocerans and Corycaeidae copepods, are poorly studied and have widely different implications for trophic transfer efficiencies to larvae. Differences in nitrogen sources - N fixation vs deep nitrate of Pacific origin - to sustain new production in the region also has implications for conditions that may select for prey types (notably cladocerans) that enhance transfer efficiency and growth rates of SBT larvae. The relative importance of these N sources for the IO ecosystem may affect SBT resiliency to projected increased ocean stratification. This research expedition investigates how mesoscale variability in new production, food-web structure and trophic fluxes affects feeding and growth conditions for SBT larvae. Sampling across mesoscale features tests hypothesized relationships linking variability in SBT larval feeding and prey preferences (gut contents), growth rates (otolith analyses) and trophic positions (TP) to the environmental conditions of waters selected by adult spawners. Trophic Positions of larvae and their prey are determined using Compound-Specific Isotope Analyses of Amino Acids (CSIA-AA). Lagrangian experiments investigate underlying process rates and relationships through measurements of water-column 14C productivity, N2 fixation, 15NO3- uptake and nitrification; community biomass and composition (flow cytometry, pigments, microscopy, in situ imaging, genetic analyses); and trophic fluxes through micro- and mesozooplankton grazing, remineralization and export. Biogeochemical and food web elements of the study are linked by CSIA-AA (N source, TP), 15N-constrained budgets and modeling. The project elements comprise an end-to-end coupled biogeochemistry-trophic study as has not been done previously for any pelagic ecosystem.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.

位于东印度洋（IO）澳大利亚西北部和印度尼西亚之间的小区域是南部蓝鳍金枪鱼（SBT）的唯一已知产卵地，SBT是一种极度濒危的顶级海洋捕食者。 成年SBT每年从高纬度觅食区迁移数千英里，在这些热带沃茨产卵，那里的食物浓度平均低于能够支持其幼虫最佳摄食和生长的水平。 这个栖息地的许多关键方面知之甚少，例如维持系统生产力的氮营养的主要来源，浮游生物食物网如何运作以产生金枪鱼幼虫喜欢的不寻常类型的浮游动物猎物，以及与海洋锋面和漩涡相关的栖息地质量的环境差异如何可能被成年产卵金枪鱼利用，以使其幼虫有更大的机会快速生长和生存成功 该项目在2021年初SBT产卵高峰期进行了为期38天的考察，调查了这些问题。 该项目是美国对第二次国际印度洋考察（IIOE-2）的贡献，该项目促进了对研究不足的东IO的地球化学和生态动力学的了解。 这是第一次详细研究连接太平洋和IO沃茨的区域的氮和碳循环。 SBT幼虫与其他大型金枪鱼和长嘴鱼物种的共同饮食偏好也可能使所获得的见解广泛适用于了解其他海洋生态系统中顶级消费者的幼虫招募问题。 这项研究提供的新信息将加强对SBT的国际管理努力。 大型金枪鱼和长嘴鱼物种共同的幼虫饮食偏好也可能将所获得的见解广泛扩展到许多其他海洋顶级消费者，包括在墨西哥湾美国沃茨产卵的大西洋蓝鳍金枪鱼。 端到端的研究方法，突出物理环境的变化，生物地球化学和浮游生物食物网之间的联系，导致魅力和经济价值的鱼类生产，是通过开发教育工具和模块的主题？学校里的科学家该项目包括佛罗里达州立大学海洋-大气预测研究中心的一个项目，通过一个为夏威夷代表性不足的学生加强STEM学习途径的项目，以及通过在圣地亚哥桦树水族馆展出的公共宣传产品。 该研究还旨在支持沉浸式的实地体验，将有才华的高中生引入海洋研究，其目标是为佛罗里达西北部农村地区代表性不足的学生开发一个可持续的海洋相关教育项目。南方蓝鳍金枪鱼（SBT）从高纬度的觅食地长途迁徙，只在热带东印度洋（IO）的一个小的贫营养区产卵这是丰富的中尺度结构，由复杂的电流和季节性逆转季风风驱动。 为了生存，SBT幼虫必须在环境条件下快速进食和生长，这挑战了对贫穷的开放海洋系统中食物网结构和功能关系的传统理解。 SBT幼虫，枝角类和Corycaeidae桡足类的首选猎物，研究甚少，并有广泛不同的影响，营养转移效率的幼虫。 氮源的差异-固氮与深硝酸盐的太平洋起源-以维持新的生产在该地区也有影响的条件，可能会选择猎物类型（特别是枝角类），提高转移效率和增长率的SBT幼虫。 这些N源的IO生态系统的相对重要性可能会影响SBT弹性预计增加海洋分层。 本次研究考察如何在新的生产，食物网结构和营养通量的中尺度变化影响SBT幼虫的摄食和生长条件。 在中尺度特征的采样测试假设的关系，连接在SBT幼虫的喂养和猎物的喜好（肠道内容物），增长率（耳石分析）和营养位置（TP）的环境条件选择成年产卵沃茨的变化。 利用氨基酸的化合物特异性同位素分析（CSIA-AA）确定幼虫及其猎物的营养位置。 拉格朗日实验通过测量水柱14 C生产力，N2固定，15 NO3吸收和硝化作用，调查潜在的过程速率和关系;社区生物量和组成（流式细胞术，色素，显微镜，原位成像，遗传分析）;和营养通量通过微型和中型浮游动物放牧，同化和出口。 生物地球化学和食物网元素的研究是由CSIA-AA（N源，TP），15 N约束的预算和建模。 该项目的组成部分包括一个端到端的耦合海洋地球化学营养研究，因为没有做过以前的任何pepagic ecosystem.This奖项反映了NSF的法定使命，并已被认为是值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估的支持。