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

概述：海洋的中水是地球上最大的生存空间。中上层食物网在生物碳泵和为商业捕捞物种生产食物方面发挥着关键作用，但其功能尚未得到充分研究，因为它的采样距离遥远，技术上具有挑战性。最近的估计表明，呼吸需求比测量的下沉颗粒供应多出2-3个数量级，这表明对中上层食物网的一些食物投入被低估或错过了。悬浮颗粒经常没有得到有效的采样，可能是一个被忽视的食物来源。由于确定有机物质对深海食物网的主要输入对于了解其功能至关重要，研究人员建议评估悬浮和下沉颗粒对北太平洋中部中上层和中上层食物网的相对重要性。它们将确定特定的中上层和中上层浮游动物和微型浮游动物的同位素组成，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，下沉和悬浮颗粒的氨基酸(AA)的增量15N和增量13C值存在差异；这些模式随着深度的变化而发散，为区分食物网路径提供了一种手段。这项研究将确定从表层到深海几个深度的悬浮和下沉颗粒的特定来源的同位素值，并测试驱动这些深度模式的微生物机制。在相应的深度，MOCNESS拖网将采样不同的后生动物：浮游动物大小的不同部分，以及目标驻留、迁徙和可能悬浮摄食的浮游动物和微型浮游动物分类群。初步数据表明，悬浮颗粒是一种次要的食物来源，与北太平洋中部表现出季节性循环通量的下沉颗粒相比，悬浮颗粒含有更少的不稳定有机物。这项研究将确定悬浮颗粒在一年中下沉颗粒通量低的时候(1月/2月)是否比在高下沉颗粒通量时(8月)对浮游动物和微型浮游动物更重要，从而能够评估表层海洋生产力的时间变化如何影响中层海洋食物网的功能。这项研究将对中、深海食物网的功能及其与北太平洋中部表层海洋过程的耦合提供新的见解。最近展示的氨基酸特定同位素分析的生态学工具将提供一种新的和全面的方法来解决我们的假设，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的15N增量值随深度增加的生态基础--显然这是一种常见的模式。浮游动物对悬浮颗粒的消耗也可能构成微生物循环和更高营养水平之间的机械联系。控制中层海洋使用者的颗粒通量的巨大衰减--从而控制向深海固碳的强度--的过程尚不清楚。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。关于渔业，许多海洋顶级捕食者，如金枪鱼和旗鱼，以中远洋微型浮游生物为食。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。广泛影响：该项目将为职业生涯早期的女性调查员(CLOSE)、女性博士后研究员以及研究生和本科生提供在领导力、研究和推广方面的极好培训机会。我们的工作产生了更广泛的社会影响，涉及渔业和气候变化，这是公众非常感兴趣的主题，我们将研究的许多动物，如鱿鱼和鳗鱼，都非常有魅力。调查人员将通过两个大众媒体场所广泛传达他们的结果。海洋之声是一档地方电视节目，可能会在公共广播公司播出，分两集重点介绍这项研究。其次，PI们将担任一部新的国际电视连续剧的顾问，大卫·阿滕伯勒的《自然好奇》将在全球范围内吸引数百万观众。

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.