SGER: Reassessing the Role of Planktonic Amoeboid Protists in Estuarine Microbial Food Webs

最近的方法学进步表明，浮游生物中裸露的变形虫(阿米巴)比之前认为的要丰富得多。利用一组新建立的生物体积关系，估计哈德逊河口浮游变形虫(HRE)的碳含量占浮游异养原生动物碳总量的3-36%，与纤毛虫相当，纤毛虫是一类受到更多研究关注的物种。因此，Amebas很可能通过河口浮游食物网在碳转移中发挥重要作用，挑战目前关于微生物通过河口浮游生物的碳通量的观点。然而，在任何海洋系统中，通过阿米巴池的C-通量都没有得到充分的量化，迄今为止，在HRE中对阿米巴的采样仅限于河口中盐碱部分的一个岸上位置。该项目将通过HRE的微生物食物网，量化裸露浮游变形虫对异养原生生物总碳和碳通量的意义。附着和自由生活的细菌以及异养原生生物的主要群体的生物量将使用基于显微镜的技术进行量化。将首次在自然条件下测量浮游变形虫的生长速度。将在3个月的时间里从HRE盐度梯度沿线的5个地点收集数据，提供从广泛环境环境中观察到的数据。其结果将是首次全面、定量地了解这一重要河口内浮游异养原生生物的现存量和C通量，并首次在任何海洋系统中充分量化浮游生物中的变形虫和其他主要原生生物类群。该项目符合SGER的指导方针，是利用最近开发的专业知识进军新兴领域的冒险，潜在地改变了我们对河口浮游微生物群落的既定看法。SGER的资金也将通过华莱士基金会资助的一个配套项目以及由O·罗杰·安德森共同为该项目提供的时间和专业知识的实物贡献而得到高度利用。植物性原生生物是从细菌到包括无脊椎动物和鱼类在内的更大生物的食物链中的重要纽带。然而，由于方法上的障碍，以前评估浮游原生生物重要性的努力忽视了浮游阿米巴的作用。该项目将结合成熟的和新可用的技术，量化阿米巴对HRE中微生物现存量和碳通量的贡献。这一努力有可能改变目前对河口浮游微生物C通量的理解。这将是第一次对HRE较低的浮游原生动物进行研究，也是第一次对河口不同地区的微生物食物网进行比较。通过提供营养水平较低的元素通量的信息，这项研究的结果将与美国人口最多的河口之一的环境管理相关。HRE为其他河口，特别是高颗粒负荷系统提供了一个模型。确定阿米巴现存量、生长速率和碳通量的环境相关性将有助于将这项研究的结果转移到其他系统。该项目与HRE中一项备受瞩目的水质研究密切相关，并受到其高度重视。这项水质研究将在网络上有大量的专门报道，并计划在未来几周内进行广泛的媒体报道。该项目还提供了一个从资深科学家(安德森)向初级同事(JUHL)转让与确定和列举浮游阿米巴有关的重要和独特知识的机会。此外，本科生将参与研究，并使用为她的高级研究论文收集的数据的一部分。

Recent methodological advances have revealed that naked amoeboid protists (amebas) are much more abundant in the plankton than previously thought. Using a newly-established set of biovolume relationships, the carbon content of planktonic amebas in the Hudson River estuary (HRE) was estimated to comprise 3-36% of total planktonic heterotrophic protist carbon, comparable to the ciliates, a group that has received much more research attention. Amebas are therefore likely to play an important role in carbon transfer through planktonic food webs in estuaries, challenging current views of microbial C fluxes through estuarine plankton. Nevertheless, C-flux through the ameba pool has not been adequately quantified in any marine system and sampling for amebas in the HRE has heretofore been restricted to a single, shore-based location in the mesohaline portion of the estuary. This project will quantify the significance of naked planktonic amebas to total heterotrophic protist carbon and C flux through the microbial food web of the HRE. Biomasses of attached and free-living bacteria and the major groups of heterotrophic protists will be quantified using microscopy-based techniques. Growth rates of planktonic amebas will be measured under natural conditions for the first time. Data will be gathered from 5 locations along the HRE salinity gradient over 3 months, providing observations from a wide range of environmental settings. The outcome will be the first comprehensive, quantitative understanding of planktonic heterotrophic protist standing stocks and C fluxes within this important estuary, and the first time amebas and other major protist groups in the plankton have been adequately quantified together in any marine system. This project meets SGER guidelines as a venture into an emerging area using recently-developed expertise to potentially transform our established view of estuarine planktonic microbial communities. SGER funding would also be highly leveraged through a companion project funded by the Wallace Foundation and by the in-kind contribution of time and expertise to the project by Co-PI, O. Roger Anderson.Planktonic protists are important links in the food web from bacteria to larger organisms, including invertebrates and fish. However, because of methodological impediments, previous efforts to assess the importance of planktonic protists have overlooked the role of planktonic amebas. Using a combination of well established and newly-available techniques, this project will quantify the contribution of amebas to microbial standing stocks and carbon fluxes in the HRE. This effort has the potential to transform current understanding of planktonic microbial C fluxes in estuaries. This will be the first study of planktonic protists in the lower HRE, and the first study to compare microbial food webs in different regions of the estuary. By providing information on elemental fluxes through lower trophic levels, the results of this study will be relevant to environmental management of one of the most populated estuaries in the US. The HRE provides a model for other estuaries, especially systems with high particle load. Determining the environmental correlates of ameba standing stocks, growth rates, and C flux will facilitate transferring the results of this study to other systems.This project is closely related to, and highly leveraged by, a high-profile study of water-quality in the HRE. The water-quality study will have a large, dedicated web presence and is slated for extensive press coverage in the coming weeks. The project also presents an opportunity for significant and unique knowledge transfer related to the identification and enumeration of planktonic amebas from a senior scientist (Anderson) to a junior colleague (Juhl). In addition, an undergraduate will participate in the research and use a portion of the data collected for her Senior research thesis.