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

在世界各地的沿海生态系统中，常被称为“死亡区”的低氧水域的出现正在增加。尽管有这些增长，但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(2毫克L-1)会导致浮游桡足类死亡、适合度降低和产卵量下降，这是支持中上层鱼类的食物网的主要环节。海上观察表明，与常氧水域(2 mg L-1)相比，低氧底层水域的桡足类丰度通常较低。氧浓度随深度下降的梯度(氧跃层)可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，成为沿海远洋生态系统的关键界面。这个项目将导致对低氧如何影响桡足类动物行为和适应能力的机械性理解。PI将比较切萨皮克湾水域经历季节性缺氧和常氧水域中对桡足类生态的自下而上和自上而下的控制。该项目的具体目标是：1)分析每小时和每周时间尺度上桡足类在尖跃层的迁徙行为和精细分布的变化，同时研究它们的食物(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)通过一系列测量(长度/重量比、摄食、产卵和卵孵化成功)估计低氧对桡足类“适合度”的影响，以制定在不同时间和深度在低氧和常氧水域捕获的桡足类条件指数；3)通过低氧诱导的低氧底层特定阶段的桡足类死亡，以及从鱼类和胶状浮游动物的捕食改变对桡足类自上而下的控制，来评估低氧对桡足类死亡的影响。面对来自鱼类和水母的捕食风险增加，桡足类可能会在一天中的部分时间在低氧水域寻求庇护，和/或在低氧水域和常氧水域之间进行短期的垂直短途旅行。通过调节垂直迁移，桡足类可能会增加对集中在尖晶石中的微型浮游动物猎物的利用。低氧水域可能会增加水母对桡足类的消耗，并抑制中上层鱼类的消耗。该项目将评估低氧和常氧水域中桡足类的分布和迁徙行为、个体适合度和特定阶段的死亡率。它将研究低氧底层水域区域中桡足类及其捕食者和猎物的空间连贯性增加或减少对食物网的影响，并将有助于从根本上理解富营养化沿海生态系统中的食物网过程。广泛的影响：随着低氧在河口和陆架水域变得更加普遍，增加对其对浮游食物网影响的了解，对于有效的基于生态系统的管理至关重要。富营养化和低氧的影响是JSOST海洋研究优先计划强调的研究领域。从该项目获得的信息将对制定切萨皮克湾渔业生态系统计划的食物网建模至关重要。从更广泛的意义上讲，为了实现切萨皮克湾计划的“切萨皮克2000”协议中的目标，这项研究是必要的。这项拟议的研究将资助两名研究生和一名博士后。此外，Horn Point实验室是大西洋中部NSF-COSEE计划的一部分，该项目将支持两名暑期教师实习生的参与。Horn Point实验室还参与了NSF本科生研究体验(REU)计划。罗伊斯大学的本科生将参与这项拟议的研究。马里兰大学环境科学中心集成和应用网络(www.ian.umces.com)的基础设施将促进向公众和环境管理人员传播成果。

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).