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

最近的研究进展表明，在浮游生物中，裸变形虫原生生物（阿米巴）的数量比以前认为的要多得多。利用一套新建立的生物体积关系，估计哈德逊河河口（HRE）浮游变形虫的碳含量占浮游异养原生生物总碳含量的3-36%，与受到更多研究关注的类群纤毛虫相当。因此，变形虫可能在河口浮游生物食物网的碳转移中发挥重要作用，挑战了目前关于河口浮游生物微生物碳通量的观点。然而，在任何海洋系统中，通过阿米巴虫池的c通量都没有得到充分的量化，而在HRE中对阿米巴虫的采样迄今为止仅限于河口中盐层部分的单一岸基位置。本项目将量化裸浮游变形虫对HRE微生物食物网中异养原生生物碳和碳总通量的意义。附着和自由生活的细菌和主要异养原生生物群体的生物量将使用基于显微镜的技术进行量化。首次在自然条件下测量浮游变形虫的生长速率。数据将在3个月内沿HRE盐度梯度从5个地点收集，提供广泛环境设置的观测结果。研究结果将首次全面定量地了解这一重要河口的浮游异养原生生物存量和碳通量，并首次在任何海洋系统中对变形虫和其他主要浮游生物类群进行充分的量化。该项目符合SGER指南，作为一个新兴领域的冒险，利用最近开发的专业知识，有可能改变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伙伴项目以及共同负责人O.罗杰·安德森对该项目的时间和专业知识的实物贡献得到高度利用。浮游原生生物是从细菌到大型生物（包括无脊椎动物和鱼类）的食物网中的重要环节。然而，由于方法上的障碍，以往评估浮游原生生物重要性的努力忽视了浮游变形虫的作用。该项目将结合现有技术和新技术，量化阿米巴对HRE微生物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碳通量的理解。这将是第一个对低HRE浮游原生生物的研究，也是第一个比较河口不同地区微生物食物网的研究。通过提供低营养水平的元素通量信息，本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。确定阿米巴现存种群、生长速率和碳通量的环境相关性将有助于将本研究的结果转移到其他系统。该项目与一项备受瞩目的HRE水质研究密切相关，并受到该研究的高度影响。这项水质研究将在一个专门的大型网站上发布，并将在未来几周内进行广泛的新闻报道。该项目还提供了一个机会，将与浮游变形虫的鉴定和枚举有关的重要和独特的知识从资深科学家（Anderson）转移到初级同事（Juhl）。此外，本科生将参与研究，并使用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.