Collaborative Research: Plankton Community Composition and Trophic Interactions as Modifiers of Carbon Export in the Sargasso Sea

来自海洋表层的颗粒碳通量受浮游生物群落的大小、分类组成和营养相互作用的影响很大。大型和/或重压载浮游植物，如硅藻和颗石藻，是碳输出的关键贡献者，因为它们的下沉率高，并通过大型浮游动物直接输出。最近，人们认识到小型无压载浮游植物通过聚集和/或营养重新包装的潜在贡献。这一认识来自实地的直接观察显示出意想不到的趋势。例如，在马尾藻海，浅水区的碳输出在过去十年中有所增加，但在此期间浮游植物群落组成的相应变化并没有朝着硅藻等较大细胞的方向发展。相反，微生态蓝藻集球藻的丰度显著增加。将聚球藻丰度增加与碳输出联系起来的营养途径尚未得到表征。这些观察结果引导研究人员研究他们的首要问题，“浮游生物的大小，群落组成和营养相互作用如何改变真光层的碳输出”。由于小型浮游植物是负责贫营养亚热带环流的初级生产的大部分，营养相互作用，包括他们必须的特点，以实现机械的理解，在海洋贫营养区的生物泵的功能。这需要对主要生物体及其生产和消费率进行全面的定性。因此，研究目标是：1）定性和定量地描述真光层中主要浮游生物群体之间的营养相互作用以及碳输出的速率和贡献者，2）根据这些数据开发一个受约束的食物网模型，这将使我们能够更好地了解当前和预测马尾藻海出口生产的近期模式。研究人员将结合实地过程研究和食物网建模，量化百慕大大西洋时间序列研究（BATS）站点生态系统关键组成部分之间的碳交换率。测量将包括一种新的，基于DNA的方法来表征和量化碳输出的非质子贡献者。在最佳可行技术试验站有充分记录的季节变化和中尺度涡旋的出现将被用作研究不同结构生态系统的自然实验室。这项研究的独特之处在于，它的目的是同时在类似的时间和空间尺度上描述多种食物网相互作用和碳输出。拟议研究的一个关键优势也是数据收集和建模组件之间的紧密联系和反馈。更广泛的影响描述生物群落和出口生产之间的复杂相互作用对于预测浮游植物物种优势，营养关系和出口生产的变化至关重要，这些变化可能发生在与气候相关的海洋环流和混合变化的情景下。这项研究也可能有助于了解生物机制，驱动当前区域到流域尺度的变化，在贫营养环流的碳输出。该提案将通过纳入学生支助，促进本科生和研究生的教育。该项目的本科生将得到亚利桑那州立大学生命科学学院本科生研究方案的部分支持，该方案旨在增加少数民族对科学的参与。基于这项研究的网络和课堂材料将通过与获奖的亚利桑那州立大学赞助的Ask A Biologist K-12网站合作开发和分发。南卡罗来纳州大学和百慕大海洋科学研究所也将加强本科生直接参与研究。

Intellectual MeritFluxes of particulate carbon from the surface ocean are greatly influenced by the size, taxonomic composition and trophic interactions of the resident planktonic community. Large and/or heavily-ballasted phytoplankton such as diatoms and coccolithophores are key contributors to carbon export due to their high sinking rates and direct routes of export through large zooplankton. The potential contributions of small, unballasted phytoplankton, through aggregation and/or trophic re-packaging, have been recognized more recently. This recognition comes as direct observations in the field show unexpected trends. In the Sargasso Sea, for example, shallow carbon export has increased in the last decade but the corresponding shift in phytoplankton community composition during this time has not been towards larger cells like diatoms. Instead, the abundance of the picoplanktonic cyanobacterium, Synechococccus, has increased significantly. The trophic pathways that link the increased abundance of Synechococcus to carbon export have not been characterized. These observations guided the investigators to their overarching research question, "How do plankton size, community composition and trophic interactions modify carbon export from the euphotic zone". Since small phytoplankton are responsible for the majority of primary production in oligotrophic subtropical gyres, the trophic interactions that include them must be characterized in order to achieve a mechanistic understanding of the function of the biological pump in the oligotrophic regions of the ocean. This requires a complete characterization of the major organisms and their rates of production and consumption. Accordingly, the research objectives are: 1) to characterize (qualitatively and quantitatively) trophic interactions between major plankton groups in the euphotic zone and rates of, and contributors to, carbon export and 2) to develop a constrained food web model, based on these data, that will allow us to better understand current and predict near-future patterns in export production in the Sargasso Sea. The investigators will use a combination of field-based process studies and food web modeling to quantify rates of carbon exchange between key components of the ecosystem at the Bermuda Atlantic Time-series Study (BATS) site. Measurements will include a novel, DNA-based approach to characterizing and quantifying planktonic contributors to carbon export. The well-documented seasonal variability at BATS and the occurrence of mesoscale eddies will be used as a natural laboratory in which to study ecosystems of different structure. This study is unique in that its aims to characterize multiple food web interactions and carbon export simultaneously and over similar time and space scales. A key strength of the proposed research is also the tight connection and feedback between the data collection and modeling components.Broader ImpactsCharacterizing the complex interactions between the biological community and export production is critical for predicting changes in phytoplankton species dominance, trophic relationships and export production that might occur under scenarios of climate-related changes in ocean circulation and mixing. This research may also help to understand the biological mechanisms that drive current regional to basin scale variability in carbon export in oligotrophic gyres. This proposal will contribute to the education of undergraduate and graduate students through the inclusion of student support. Undergraduate students in this project will be partly supported through Arizona State University (ASU)'s School of Life Sciences Undergraduate Research Program which seeks to increase the participation of minorities in science. Web and classroom materials based on this research will be developed and distributed through a partnership with the award-winning ASU-sponsored Ask A Biologist K-12 Web site. Direct undergraduate involvement in research will also be enhanced at the University of South Carolina and the Bermuda Institute of Ocean Sciences.