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

概述：海洋的中层水域是地球上最大的生活空间。中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，但其功能研究不足，因为它距离遥远，取样技术上具有挑战性。最近的估计表明，呼吸需求超过测量下沉颗粒供应多达2-3个数量级，这表明对中层食物网的一些食物投入被低估或错过。悬浮颗粒物经常没有得到有效的采样，可能是一个被忽视的食物来源。由于确定有机物对深海食物网的主要投入对于了解其功能至关重要，调查人员提议评价悬浮颗粒和下沉颗粒对北太平洋中部中层和深层食物网的相对重要性。他们将确定特定的中层和深层浮游动物和微浮游生物群体的同位素组成特征，并使用质量平衡方法确定它们消耗悬浮或下沉颗粒的程度。研究人员最近已经认识到下沉和悬浮颗粒的氨基酸（AA）的δ 15 N和δ 13 C值的差异;这些模式随深度而不同，提供了一种区分食物网途径的方法。这项研究将确定从表层到深海层几个深度的悬浮和下沉颗粒的特定来源同位素值，并测试驱动这些深度模式的拟议微生物机制。在相应的深度，MOCNESS拖网将采样不同的后生动物：浮游动物大小的部分，加上目标居民，迁移和可能悬浮喂养浮游动物和微浮游生物分类群。初步数据表明，悬浮颗粒是一个次要的食物来源，含有较少的不稳定的有机物质比下沉颗粒，表现出季节性周期的流量在北太平洋中部。这项研究将确定在一年中沉降颗粒通量较低的时候（1月/2月）与沉降颗粒通量较高的时候（8月）相比，悬浮颗粒对浮游动物和微浮游生物是否变得更加重要，从而可以评估表层海洋生产力的时间变化如何影响中层食物网的功能。智力优势：最近的研究要求对海洋深层中层水域进行更多的研究。这项研究将为了解中层和深层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异性同位素分析的生态工具将提供一种新颖而全面的方法来解决我们的假设，该项目将开发第一个跨越粒子到鱼类的AA同位素数据集。结果将有助于确定三角洲15 N值随浮游动物深度增加的生态基础-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和更高营养级之间的机械联系。控制中层消费者颗粒通量大幅衰减的过程-从而控制深海固碳的强度-尚不清楚。季节性取样将有助于我们将中层食物网进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，金枪鱼和箭鱼等许多海洋顶级掠食者以中层微浮游生物为食。更清楚地了解中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：本项目将为一名职业生涯初期的女性调查员（Close）、一名女性博士后研究员以及一名研究生和一名本科生提供领导力、研究和推广方面的绝佳培训机会。我们工作的更广泛的社会影响涉及渔业和气候变化，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场所广泛传播他们的结果。《海洋之声》是一个当地的电视节目，有可能在PBS上播出，这将在两集中突出这项研究。第二，PI将担任一个新的国际电视连续剧，大卫阿滕伯勒的“自然好奇心”，将达到数百万观众的国际顾问。

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.