RUI: Ecophysiology of gelatinous zooplankton in hypoxic estuaries

河口在夏季通常是自然缺氧的地方，原因有几个：淡水流入减少，周转时间减少，分层增加，地表初级生产力增加下沉到底部，在那里重新矿化，从而耗尽氧气。普吉特海湾周围人口增长的增加，通过增加营养物质的流入和由此导致的富营养化，增加了河口近底部深处的缺氧程度。切萨皮克湾的研究人员发现，胶状浮游动物能够在低氧的底层水域中生存，而它们的浮游动物猎物(桡足类和鱼类幼虫)无法忍受如此低水平的氧气。这意味着猎物集中在浅水区，而胶状捕食者可以利用垂直迁徙的好处。因此，由于人类干扰导致河口缺氧程度的增加，似乎通过增加胶状捕食者的重要性来改变远洋鱼类的食物网络结构。本项目将研究胶状浮游动物在低氧水平下存活的机制。先前对水母、鞭毛虫、毛网虫和其他中层含氧量最低层的远洋蠕虫的代谢生理学的研究使研究者提出了几种机制，使没有氧结合蛋白或循环系统发育良好的简单动物可以在低氧环境中生存。胶状浮游动物从高氧水转移到氧气枯竭的水中，将氧气泄漏到一个封闭的小室中(Thuesen和Amp；Chilresse，未发表；Thuesen和Amp；Lee，未发表)，该项目将描述和量化中层胶状浮游动物在进军低氧河口水域期间向胶状浮游动物提供氧气的储氧能力。该项目还将调查河口胶状浮游动物潜在的糖酵解适应情况，包括鞭毛虫、水母和弓形水母。本研究的目的是：(1)确定胶状浮游动物的氧调节能力；(2)测量中胶状浮游动物的氧气释放速率与周围水中氧浓度的函数关系，并确定氧释放是否受生物体的调节；(3)通过生化测量确定“储氧潜力”与代谢活性组织的比率，并开发胶状浮游动物耐缺氧指数，以预测不同物种可能具有的低氧生存能力；以及(4)确定厌氧代谢在胶状浮游动物耐缺氧中可能起到的作用。本文提出的研究将通过与马里兰大学和自然科学院河口研究中心的科学家合作，补充切萨皮克湾低氧区胶状浮游动物的研究，这将允许使用从切萨皮克湾低氧区收集的标本进行研究。这项拟议的研究将通过与华盛顿州生态部海洋水质监测小组的合作，进一步加深我们对低氧对Puget Sound食物网影响的了解。长青州立学院的学生将通过建议的RUI活动参与这项研究而受益。

Estuaries are typically sites of natural hypoxia in summer for several reasons: lower freshwater inflows decrease turnover times, stratification increases, and increased surface primary production sinks to the bottom where it is remineralized thereby using up oxygen. Increased human population growth around the Puget Sound has increased the degree of hypoxia in the near-bottom depths of the estuary through increased nutrient influx and resulting eutrophication. Researchers in Chesapeake Bay have found that gelatinous zooplankton are able to survive in hypoxic bottom waters while their zooplankton prey (copepods and fish larvae) cannot tolerate such low levels of oxygen. This means that prey are concentrated in shallower zones while gelatinous predators can take advantage of the benefits of vertical migration. Therefore, increased hypoxia in estuaries due to human disturbances appears to alter pelagic food web structure by increasing the importance of gelatinous predators.This project will investigate the mechanisms that allow gelatinous zooplankton to survive at low oxygen levels. Previous research on the metabolic physiology of medusae, ctenophores, chaetognaths and other pelagic worms in midwater oxygen minimum layers has led the Investigator to propose several mechanisms whereby simple animals that do not have oxygen binding proteins or well developed circulatory systems may survive in low oxygen environments. Gelatinous zooplankters transferred from high-oxygen water to water depleted in oxygen leak oxygen into a closed chamber (Thuesen & Childress, unpublished; Thuesen & Lee, unpublished), and this project will describe and quantify the oxygen storage capabilities of mesoglea in the context of providing oxygen to gelatinous zooplankters during forays into hypoxic estuarine waters. This project will also investigate potential glycolytic adaptations in estuarine gelatinous zooplankton, including ctenophores, hydromedusae and scyphomedusae. The goals of this research are to (1) determine the oxygen regulatory abilities of gelatinous zooplankton; (2) measure the rate of oxygen release from mesoglea as a function of oxygen concentration in the surrounding water and determine if oxygen release is regulated by the organism; (3) determine the ratios of "oxygen storage potential" to metabolically active tissue through biochemical measurements and develop indices of hypoxia tolerance in gelatinous zooplankton to predict the abilities that different species may have for hypoxia survival; and (4) determine the role that anaerobic metabolism may have in the hypoxia tolerance of gelatinous zooplankton.The studies proposed here will complement studies on gelatinous zooplankton in hypoxic regions of the Chesapeake Bay through collaborations with scientists at the University of Maryland and the Estuarine Research Center of the Academy of Natural Sciences that will allow studies with specimens collected from hypoxic zones of the Chesapeake Bay. The proposed research will further our knowledge on the impact of hypoxia on Puget Sound food webs through collaborations with the Washington State Department of Ecology Marine Water Quality Monitoring Team. Students at The Evergreen State College will benefit through participation in this research through proposed RUI activities.