Bringing Out the Dead: Distribution and microbial decomposition of copepod carcasses in the marine environment

浮游动物研究的一个基本需求是准确评估自然界中的浮游动物种群数量。传统上，研究人员收集、保存和计数浮游动物，而不考虑浮游动物的活/死状态。然而，最近的研究表明，浮游动物可能遭受相当程度的非消耗性(非捕食性)死亡，它们的身体有时在海洋环境中可能大量存在。如果不能在自然样本中区分活的和死的浮游动物，科学家们将误解许多基本的远洋过程。由于浮游动物身体也是细菌和其他微生物的丰富底物来源，它们在海洋中的存在也可能影响水柱中的微生物过程和组成。PI最近改进和测试了一种生命染色方法，使他们能够很容易地在自然样本中分离活的和死的浮游动物，特别是桡足类动物。该方法简单、价廉，并与常规采样方案兼容。切萨皮克湾的实地研究发现，2005年和2006年夏天，相当一部分桡足类种群死亡。实验室实验进一步表明，桡足类身体是有利于特定细菌系统型的活动和生长的微生物热点，并为周围水域贡献新的细菌。这些观察结果表明，需要进一步研究天然桡足类种群的活/死组成，以及它们对环境微生物活动和组成的贡献。该项目将把生命染色方法的应用范围扩大到不同的桡足类发育阶段和不同的浮游动物群体。为期一年的例行采样将在切萨皮克湾的不同地区进行。多变量分析将被用来探索活的/死的桡足类组成与各种水文参数之间的预测关系。实验室实验将量化因下沉和微生物分解而造成的身体损失率。现代分子技术将被用来研究分解过程中细菌群落组成的变化。然后，现场和实验室数据将在建模工作中结合起来，以估计特定物种和阶段的非消耗性死亡率。国际浮游动物研究所将与来自世界各地的研究人员协调，研究截然不同的海洋生态系统中浮游动物的活体/死亡数量和分布，向在全球范围内了解非消耗性浮游动物死亡率迈出重要的一步。该项目的成果将从根本上改变我们对海洋环境中浮游动物生态和次生生产的认识，并有助于改进海洋监测方案和现有的桡足类种群动态模型。PI将领导全球与几个国际研究小组在应用染色方法方面的协调努力，并产生关于世界不同地区活的/死的桡足类组成的前所未有的科学信息。学生教育是该项目不可或缺的一部分。一名博士生将在该项目中与许多国际研究小组密切合作。本科生实习生将通过VIMS现有的DREAM和REU计划招聘。除了明显的科学利益外，这种国际合作还可以让来自不同文化背景的研究人员相互交流和学习，促进他们之间未来的合作，并有助于推动参与国的海洋研究。国际和平协会将通过研讨会、讲习班、特别课程和会议积极吸引合作机构的教职员工和学生，以扩大该项目的教育影响。

A basic need in zooplankton research is accurate assessment of zooplankton population abundance in nature. Traditionally researchers collect, preserve and enumerate zooplankton disregarding the live/dead status of the zooplankton. However, recent studies have shown that zooplankton can suffer significant level of non-consumptive (non-predatory) mortality and their carcasses can be abundant at times in the marine environments. Without distinguishing between live and dead zooplankton in natural samples scientists would misunderstand many fundamental pelagic processes. Because zooplankton carcasses are also rich substrate sources for bacteria and other microbes, their presence in the ocean also potentially affects microbial processes and composition in the water column. A vital stain method recently refined and tested by the PI allows them to easily separate live and dead zooplankton, especially copepods, in natural samples. The method is simple, inexpensive, and compatible with common routine sampling protocols. Field studies in the Chesapeake Bay found a substantial portion of the copepod populations dead in the summers of 2005 and 2006. Laboratory experiments further showed that copepod carcasses were 'microbial hotspots' that favor the activity and growth of specific bacterial phylotoypes, and contribute new bacteria to the surrounding water. These observations pointed to the need for further study of the live/dead composition of natural copepod populations, and their contribution to ambient microbial activities and composition. This project will expand the application of the vital stain method to different copepod developmental stages and different zooplankton groups. Year-long routine samplings will be conducted in different parts of the Chesapeake Bay. Multivariate analysis will be used to explore predictive relationships between live/dead copepod composition and various hydrographic parameters. Laboratory experiments will quantify the loss rates of carcasses due to sinking and microbial decomposition. Modern molecular techniques will be used to investigate the shift in bacterial community composition during the decomposition process. Field and lab data will then be combined in a modeling effort to estimate species- and stage-specific non-consumptive mortality. The PI will coordinate with researchers from around the world to study live/dead zooplankton abundance and distribution in vastly different marine ecosystems, taking an important step toward understanding non-consumptive zooplankton mortality on the global scale. Results of this project will fundamentally change our understanding of zooplankton ecology and secondary production in the marine environment, and help improve marine monitoring programs and existing copepod population dynamic models. The PI will lead a global concerted effort with several international research groups in the application of the staining method, and produce unprecedented scientific information on the live/dead copepod composition in different parts of the world. Student education is an integral part of the project. A Ph.D. student will work closely with many international research groups in the project. Undergraduate interns will be recruited through the existing DREAMS and REU programs at VIMS. Besides the obvious scientific benefits, this international collaboration also allows researchers from very different cultural backgrounds to interact and learn from each other, stimulate future collaborations among them, and help advance oceanographic research in the participating countries. The PI will actively engage faculty and students in the partner institutions through seminars, workshops, special courses and conferences, aiming to broaden the educational impacts of the project.