Evaluating the relative importance of suspended and sinking particles to the meso and bathypelagic food web in the central North Pacific

概述：海洋的中部水域是地球上最大的生存空间。中上层食物网在生物碳泵和商业收获物种的食物生产中起着关键作用，但其功能尚未得到充分研究，因为它距离遥远，在技术上具有挑战性。最近的估计表明，呼吸需求比测量到的下沉颗粒供应高出2-3个数量级，这表明中上层食物网的一些食物输入被低估或遗漏了。悬浮颗粒经常不能有效取样，可能是被忽视的食物来源。由于确定深海食物网的主要有机物输入对于理解其功能至关重要，研究人员建议评估悬浮和下沉颗粒对北太平洋中部中远洋和深海食物网的相对重要性。他们将描述中远洋和深海浮游动物和微浮游动物特定群体的同位素组成特征，并利用质量平衡方法确定它们消耗悬浮或下沉颗粒的程度。研究人员最近发现下沉颗粒和悬浮颗粒的氨基酸（AA）的δ 15N和δ 13C值存在差异；这些模式随着深度的不同而不同，提供了一种区分食物网路径的方法。该研究将确定从表面到深海的几个深度的悬浮和下沉颗粒的来源特定同位素值，并测试驱动这些深度模式的微生物机制。在相应的深度，MOCNESS拖网将采集不同的后生动物样本：浮游动物大小的部分，以及目标的常驻、迁徙和可能悬浮进食的浮游动物和微浮游动物分类群。初步数据表明，悬浮颗粒是次级食物来源，与北太平洋中部呈现季节性循环流动的下沉颗粒相比，悬浮颗粒含有较少的不稳定有机质。这项研究将确定悬浮颗粒在下沉颗粒通量低（1月/ 2月）和高（8月）期间是否对浮游动物和微浮游生物更重要，从而评估海洋表面生产力的时间变化如何影响中上层食物网的功能。知识价值：最近的研究呼吁对海洋的深水进行更多的研究。这项研究将为北太平洋中部中远洋和深海食物网的功能及其与表层海洋过程的耦合提供新的见解。最近展示的氨基酸特异性同位素分析的生态工具将为解决我们的假设提供一种新颖而全面的方法，该项目将开发第一个跨越颗粒到鱼类的AA同位素数据集。结果将有助于确定浮游动物中三角洲15N值随深度增加的生态基础——这显然是一种常见的模式。浮游动物对悬浮颗粒的消耗也可能构成微生物循环与更高营养水平之间的机制联系。控制中远洋消费者对颗粒通量的巨大衰减的过程——以及因此对深海碳固存的强度——尚不清楚。季节性采样将帮助我们将中上层食物网过程与表层海洋生产力的变化联系起来，进一步了解未来气候变化对深海食物网和碳通量的影响。在渔业方面，许多海洋顶级捕食者，如金枪鱼和剑鱼，以中远洋微藻为食。更清楚地了解中上层食物网的结构将有助于为用于了解渔业生产变化的生态系统模型提供信息。更广泛的影响：该项目将为一名早期职业女性研究者（Close）、一名女性博士后研究员、一名研究生和一名本科生提供优秀的领导力、研究和外联培训机会。我们的工作对渔业和气候变化有更广泛的社会影响，这是公众非常感兴趣的主题，我们将研究的许多动物，如鱿鱼和琵琶鱼，都非常有魅力。调查人员将通过两个大众媒体广泛传播他们的结果。《海之声》是一个地方电视节目，可能会在PBS播出，其中两集将重点介绍这项研究。其次，两位首席检察官将担任一部新的国际电视剧的顾问，这部电视剧名叫大卫·阿滕伯勒（David Attenborough）的《自然好奇心》（Natural Curiosities），将吸引全球数百万观众。

Overview: The ocean's midwaters are the largest living space on the planet. The mesopelagic food web plays key roles in the biological carbon pump and the production of food for commercially harvested species, but its functioning is understudied because it is remote and technologically challenging to sample. Recent estimates indicate respiratory demand outstrips measured sinking particle supply by up to 2-3 orders of magnitude suggesting that some food inputs to the mesopelagic food web have been underestimated or missed. Suspended particles frequently are not sampled effectively and may be an overlooked food source. Because identifying the principal inputs of organic matter to the deep-sea food web is critical to understanding its function, the investigators propose to evaluate the relative importance of suspended and sinking particles to the meso- and bathypelagic food web in the central North Pacific. They will characterize the isotopic compositions of specific groups of mesopelagic and bathypelagic zooplankton and micronekton, and identify the extent to which they consume suspended or sinking particles using mass balance approaches. The investigators recently have recognized differences in delta 15N and delta 13C values of amino acids (AA) of sinking and suspended particles; these patterns diverge with depth, providing a means to distinguish between food web pathways. The research will define the source-specific isotopic values of suspended and sinking particles at several depths from the surface to the bathypelagic and test proposed microbial mechanisms driving these depth patterns. At corresponding depths, MOCNESS trawls will sample diverse metazoa: zooplankton size fractions, plus targeted resident, migrating and likely suspension-feeding taxa of zooplankton and micronekton. Preliminary data suggest that suspended particles are a secondary food source, containing less labile organic matter than sinking particles that exhibit a seasonal cycle in flux in the central North Pacific. This study will determine if suspended particles become more important to zooplankton and micronekton during a time of year when sinking particle flux is low (Jan/Feb) in comparison to when it is high (Aug), allowing an evaluation of how temporal change in surface ocean productivity affects the functioning of mesopelagic food webs.Intellectual Merit: Recent research has called for additional study of the ocean's deep midwaters. This study will provide new insights into the functioning of the meso- and bathypelagic food web and its coupling with surface ocean processes in the central North Pacific. The recently-demonstrated ecological tool of amino acid-specific isotopic analysis will provide a novel and comprehensive approach with which to address our hypotheses, and the project will develop the first AA isotopic dataset spanning particles to fish. Results will help identify the ecological underpinnings of increasing delta 15N values with depth in zooplankton -- apparently a common pattern. Zooplankton consumption of suspended particles also could constitute a mechanistic link between the microbial loop and higher trophic levels. The processes controlling the enormous attenuation of particle flux by mesopelagic consumers -- and thereby the strength of carbon sequestration to the deep ocean -- are not understood. Seasonal sampling will help us relate mesopelagic food web processes to changes in surface ocean productivity, furthering our understanding of future climate change impacts on deep-sea food webs and carbon flux. With regard to fisheries, many oceanic top predators such as tuna and swordfish feed on mesopelagic micronekton. A clearer understanding of the structure of mesopelagic food webs will help inform ecosystem models which are used to understand variation in fisheries production.Broader Impacts: This project will provide excellent training opportunities in leadership, research and outreach for an early-career female investigator (Close), a female postdoctoral researcher and for a graduate student and an undergraduate student. Broader societal impacts of our work relate to fisheries and climate change, subjects of great interest to the public, and many of the animals we will study, such as squid and anglerfishes, are very charismatic. The investigators will broadly communicate their results through two mass media venues. Voices of the Sea is a local TV program, with potential distribution to PBS that will highlight the research in two episodes. Second, the PIs will act as advisors for a new international TV series, David Attenborough's "Natural Curiosities" that will reach millions of viewers internationally.