Collaborative Research: Hypoxia in Marine Ecosystems: Implications for Neritic Copepods

低氧水域（通常被称为“死区”）在全世界沿海生态系统中的出现正在增加。尽管有这些增加，但人们对低氧水域对远洋食物网的影响仍然知之甚少。实验室研究表明，低氧水（2mg -1）会导致浮游桡足类动物死亡、健康降低和产卵减少，浮游桡足类动物是支持远洋鱼类的食物网的主要环节。在海洋中的观察表明，与正常氧水（2 mg -1）相比，低氧的底水通常有较低的桡足类丰度。氧浓度随深度下降的梯度（氧跃层）可以通过改变桡足类的迁徙行为和深度分布以及它们与潜在捕食者和猎物的空间一致性，成为沿海中上层生态系统的关键界面。这个项目将导致对缺氧如何影响桡足类动物的行为和适应性的机制理解。pi将比较在切萨皮克湾经历季节性缺氧和正常缺氧的水域中，自下而上和自上而下对桡足动物生态的控制。该项目的具体目标是：1)在每小时和每天的时间尺度上，分析桡足类动物在氧层上的迁徙行为和精细（米）分布的变化，同时检查它们的食物（浮游植物和微型浮游动物）和捕食者（鱼类、胶状浮游动物）的分布和丰度；2)利用一套测量方法（长重比、摄食、产蛋量和卵孵化成功率）估算低氧对桡足类“适合度”的影响，建立在低氧和常氧水域中不同时间和深度捕获的桡足类的状态指数；3)通过低氧海底低氧诱导的、特定阶段的桡足动物死亡率，以及鱼类和胶状浮游动物捕食对桡足动物自上而下控制的变化，评估低氧对桡足动物死亡率的影响。氧离子可能是桡足类垂直迁移的障碍，从而破坏了捕食者的躲避行为。面对鱼类和水母捕食风险的增加，桡足类动物可能会在低氧水域中寻找避难所，或者在低氧和常氧水域之间进行短期的垂直旅行。桡足类通过调节垂直迁徙，增加了对集中在氧斜区的浮游微动物猎物的利用。低氧水域可能会增加水母对桡足类动物的消耗，抑制远洋鱼类的消耗。该项目将评估低氧和常氧水域中桡足动物的分布和迁徙行为、个体适应度和阶段特异性死亡率。它将研究低氧水底地区桡足类及其捕食者和猎物空间一致性增加或减少对食物网的影响，并将有助于对富营养化沿海生态系统食物网过程的基本理解。更广泛的影响：随着缺氧在河口和陆架水域变得越来越普遍，增加对其对浮游食物网的影响的了解对于有效的、基于生态系统的管理至关重要。富营养化和缺氧的影响是JSOST海洋研究优先计划强调的研究领域。从该项目中获得的信息将对切萨皮克湾渔业生态系统计划发展中的食物网建模至关重要。在更广泛的意义上，研究是需要实现在切萨皮克湾计划的“切萨皮克2000”协议的目标。这项拟议的研究将资助两名研究生和一名博士后。此外，角点实验室是中大西洋NSF-COSEE项目的一部分，该项目将支持两名暑期教师实习生的参与。角点实验室还参加了美国国家科学基金会本科生研究经验（REU）计划。REU的本科生将参与拟议的研究。马里兰大学环境科学中心综合和应用网络（www.ian.umces.com）的基础设施将促进向公众和环境管理人员传播结果。

The occurrence of low-oxygen waters, often called "dead zones" in coastal ecosystems throughout the world is increasing. Despite these increases, the pelagic food-web consequences of low-oxygen waters remain poorly understood. Laboratory research has demonstrated that hypoxic water ( 2 mg l-1) can result in mortality, reduced fitness and lower egg production of planktonic copepods, a major link in food webs supporting pelagic fish. Observations in the sea indicate that hypoxic bottom waters usually have depressed abundances of copepods compared to normoxic waters ( 2 mg l-1). The gradient of declining oxygen concentration with respect to depth (oxycline) can be a critical interface in coastal pelagic ecosystems by altering the migratory behavior and depth distribution of copepods and their spatial coherence with potential predators and prey. This project will result in a mechanistic understanding of how behavior and fitness of copepods are affected by hypoxia. The PIs will compare bottom-up and top-down controls on the ecology of copepods in Chesapeake Bay waters experiencing seasonal hypoxia and those that are normoxic. Specific objectives of this project are to: 1) analyze changes in migratory behavior and fine-scale (meter) distribution of copepods across the oxycline over hourly and diel time scales while simultaneously examining the distribution and abundance of their food (phytoplankton and microzooplankton) and predators (fish, gelatinous zooplankton); 2) estimate effects of hypoxia on the "fitness" of copepods using a suite of measurements (length/weight ratios, feeding, egg production, and egg hatching success) to develop condition indices of copepods captured at different times and depths in hypoxic and normoxic waters; and 3) evaluate effects of hypoxia on copepod mortality by hypoxia-induced, stage-specific copepod mortality in hypoxic bottom waters and by changes in top-down control of copepods from predation by fish and gelatinous zooplankton.Oxyclines may be a barrier to vertical migration of copepods and thus disruptive to predator avoidance behavior. Faced with increased predation risk from fish and jellyfish, copepods may seek refuge in hypoxic waters for part of the day and/or make short-term vertical excursions between hypoxic and normoxic waters. By regulating vertical migrations, copepods may increase utilization of microzooplankton prey concentrated in the oxycline. Hypoxic waters may elevate consumption of copepods by jellyfish and depress consumption by pelagic fish. This project will evaluate copepod distribution and migration behavior, individual fitness and stage-specific mortality in hypoxic and normoxic waters. It will examine food-web consequences of increased or decreased spatial coherence of copepods and their predators and prey in regions with hypoxic bottom waters and will contribute to fundamental understanding of food-web processes in eutrophic coastal ecosystems.Broader Impacts: As hypoxia becomes more prevalent in estuarine and shelf waters, increased understanding of its effects on planktonic food-webs becomes essential for effective, ecosystem-based management. The effects of eutrophication and hypoxia are areas of research emphasized in the JSOST Ocean Research Priorities Plan. Information gained from this project will be critical for food-web modeling in development of fisheries ecosystem plans for Chesapeake Bay. In a broader sense, the research is needed to achieve goals in the Chesapeake Bay Program's "Chesapeake 2000" Agreement. The proposed research will support two graduate students and a postdoc. In addition, the Horn Point Laboratory is part of the mid-Atlantic NSF-COSEE program and this project will support the participation of two summer teacher interns. The Horn Point Laboratory also participates in the NSF Research Experience for Undergraduates (REU) program. REU undergraduate students will be involved in the proposed research. Dissemination of results to the public and environmental managers will be facilitated by the infrastructure of University of Maryland Center for Environmental Science's Integration and Application Network (www.ian.umces.com).