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: 2404504
• 负责人: Sven Kranz
• 金额: $ 52.78万
• 依托单位: William Marsh Rice University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2023
• 资助国家: 美国
• 起止时间: 2023-10-01 至 2024-09-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=2404504&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.

东印度洋 (IO) 澳大利亚西北部和印度尼西亚之间的小片区域是南蓝鳍金枪鱼 (SBT) 唯一已知的产卵地，南蓝鳍金枪鱼是一种极度濒危的顶级海洋捕食者。 成体 SBT 每年从高纬度觅食区迁徙数千英里，在这些热带水域产卵，这些热带水域的食物浓度平均低于可以支持幼虫最佳摄食和生长的水平。 该栖息地的许多关键方面鲜为人知，例如维持系统生产力的氮养分的主要来源、浮游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，以及栖息地质量的环境差异如何相关产卵的成年金枪鱼可能会利用海滨和涡流为其幼鱼提供更大的快速生长和成功生存的机会。 该项目在 2021 年初 SBT 产卵高峰期进行了为期 38 天的考察，对这些问题进行了调查。 该项目是美国对第二次国际印度洋考察 (IIOE-2) 的贡献，旨在增进对研究较少的印度洋东部生物地球化学和生态动力学的了解。 这是对连接太平洋和印度洋水域的区域的氮和碳循环的首次详细研究。 SBT 幼体与其他大型金枪鱼和旗鱼物种的共同饮食偏好也可能使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体招募问题。 该研究的新信息将加强 SBT 的国际管理工作。 大型金枪鱼和长嘴鱼幼体的共同饮食偏好也可能将广泛获得的见解扩展到许多其他海洋顶级消费者，包括在墨西哥湾美国水域产卵的大西洋蓝鳍金枪鱼。 端到端的研究方法强调了物理环境变化、生物地球化学和浮游生物食物网之间的联系，从而产生具有魅力和经济价值的鱼类生产，这是通过“学校科学家”开发教育工具和模块的主题？佛罗里达州立大学海洋大气预测研究中心的项目，通过一项旨在加强夏威夷代表性不足的学生的 STEM 学习途径的项目，以及通过在圣地亚哥伯奇水族馆展示的公共宣传产品。 该研究还旨在支持沉浸式实地体验，向有才华的高中生介绍海洋研究，目标是为佛罗里达州西北部农村地区代表性不足的学生制定可持续的海洋相关教育计划。 南方蓝鳍金枪鱼 (SBT) 从远距离迁徙高纬度觅食地，仅在热带东印度洋（IO）的一个小型寡营养区域产卵，该区域富含中尺度结构，受到复杂的洋流和季节性反转季风的驱动。 为了生存，SBT 幼虫必须在环境条件下快速进食和生长，这挑战了对贫困开放海洋系统中食物网结构和功能关系的传统理解。 SBT 幼虫的首选猎物枝角动物和 Corycaeidae 桡足类动物的研究很少，并且对幼虫的营养转移效率具有广泛不同的影响。 氮源的差异（固氮与太平洋来源的深层硝酸盐）维持该地区的新生产也对可能选择猎物类型（尤其是枝角动物）的条件产生影响，从而提高了 SBT 幼虫的转移效率和生长速度。 这些氮源对 IO 生态系统的相对重要性可能会影响 SBT 对预计的海洋分层增加的弹性。 这项研究考察了新产量、食物网结构和营养通量的中尺度变异如何影响 SBT 幼虫的摄食和生长条件。 跨中尺度特征的采样测试了假设的关系，这些关系将 SBT 幼虫摄食和猎物偏好（肠道内容物）、生长速率（耳石分析）和营养位置（TP）的变异性与成虫产卵者选择的水域环境条件联系起来。 使用化合物特异性氨基酸同位素分析 (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 14C 生产力、N2 固定、15NO3- 吸收和硝化作用来研究潜在的过程速率和关系；群落生物量和组成（流式细胞术、色素、显微镜、原位成像、遗传分析）；以及通过微型和中型浮游动物放牧、再矿化和出口产生的营养通量。 该研究的生物地球化学和食物网要素通过 CSIA-AA（N 源，TP）、15N 约束预算和模型联系起来。 该项目要素包括一项端到端耦合的生物地球化学-营养研究，这是以前从未对任何远洋生态系统进行过的研究。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值和更广泛的影响审查进行评估，被认为值得支持标准。