Collaborative Research: Quantifying competing loss rates of viral lysis and microzooplankton grazing on Emiliania huxleyi mortality

促进生长或导致死亡的过程驱动着所有生物的丰度。对于浮游植物这样的微生物来说，它们的寿命以小时到天为单位，这些过程中的微小变化可能会产生重大影响。浮游植物是整个海洋环境中物质和营养物质流动的核心货币。即使它们的生长和死亡率发生很小的变化，也会对生态系统结构和生物地球化学循环产生大规模影响。虽然经常检查影响生长的因素，但对浮游植物死亡率的调节知之甚少。该项目将侧重于量化形成水华的球石藻（Emiliania huxleyi）的竞争死亡模式，这是一种全球重要的浮游植物物种，对海洋碳和硫循环有重要贡献。单细胞微型浮游动物的放牧造成的死亡是海洋环境中浮游植物损失的最大原因。然而，赫胥黎肠杆菌也与一种可导致大规模死亡的病毒有明显的关系。因此，赫胥黎梭菌可以作为一个很好的模式生物，用于研究浮游微动物捕食和病毒感染导致的分解之间的死亡率是如何划分的。量化这些死亡机制将有助于建立准确预测赫胥黎种群动态变化的数学模型，并最终预测初级生产和生物地球化学循环。这项工作将涉及在一个学校系统中与一名高中科学教师合作，该学校系统中有很大比例的学生来自代表性不足的群体，在创作和实施描述重要生态相互作用的短片剪辑中。这些影片片段将被整合到实验活动中，向学生传达这些概念。此外，来自代表性不足群体的本科生将在伍兹霍尔海洋学研究所和罗格斯大学接受培训，对浮游植物的死亡过程进行实验室研究。这项研究还将为博士后科学家提供培训和职业发展。浮游植物的死亡机制通常是相互独立的，但在自然界中，这些过程是同时发生的。微小浮游动物的掠食和病毒裂解对赫胥黎氏菌总体损失的相对比例以及它们如何相互作用以形成水华动态在很大程度上是未知的。了解这些过程的相对重要性及其相互作用是至关重要的，因为它们对海洋食物网和生物地球化学循环的结构和功能有截然不同的影响。虽然放牧倾向于将浮游植物生物量引导到更高的营养水平，但病毒裂解刺激微生物环的活动和垂直颗粒出口通量。本研究将在实验室和野外环境实验中确定一种死亡过程对另一种死亡过程的影响，以及它们对赫胥黎种群动态和出口的净影响。这种综合方法将为多营养微生物相互作用提供独特的机制视角，从而增加赫胥黎菌种群动态和生物地球化学循环的准确预测潜力。这项研究的结果有可能对微生物相互作用如何驱动海洋环境中的生态和生物地球化学动力学产生广泛适用的见解。

Processes that either promote growth or cause mortality drive the abundance of all organisms. For microbes such as phytoplankton, that have a lifespan measured in hours to days, small changes in these processes can have significant impacts. Phytoplankton are the central currency in the flow of material and nutrients throughout the marine environment. Even small shifts in their growth and mortality rates will have large-scale implications for ecosystem structure and biogeochemical cycling. While factors that influence growth are often examined, less is known regarding the regulation of phytoplankton mortality. This project will focus on quantifying competing modes of mortality on the bloom-forming coccolithophore, Emiliania huxleyi, a globally important phytoplankton species that contributes significantly to ocean carbon and sulfur cycles. Mortality due to grazing by single-celled microzooplankton is the largest contributor to phytoplankton loss in the marine environment. However, E. huxleyi also has a well-characterized relationship with a virus that can result in mass mortality. Therefore, E. huxleyi serves as a good model organism for examining how mortality is partitioned between grazing by microzooplankton predators and lysis due to viral infection. Quantifying these mortality mechanisms will help to inform mathematical models for the accurate prediction of shifts in E. huxleyi population dynamics and ultimately, primary production and biogeochemical cycling. This work will involve collaboration with a high school science teacher in a school system with a large proportion of students from underrepresented groups, in the creation and implementation of short film clips that depict important ecological interactions. These film clips will then be incorporated into laboratory activities to communicate these concepts to students. Further, undergraduate students from underrepresented groups will be trained at both Woods Hole Oceanographic Institute and Rutgers University, to perform laboratory research on mortality processes on phytoplankton. This research will also provide training and career development for a postdoctoral scientist.Mortality mechanisms in phytoplankton have generally been studied independent from one another, however in nature, these processes act concurrently. The relative proportion that microzooplankton grazing and viral lysis contribute to overall E. huxleyi loss and how they may interact to shape bloom dynamics is largely unknown. Understanding the relative importance of these processes, as well as their interaction, is critical due to their contrasting influence on the structure and function of marine food webs and biogeochemical cycles. While grazing tends to channel phytoplankton biomass to higher trophic levels, viral lysis stimulates microbial loop activity and vertical particle export flux. This research will determine the effect of one mortality process on the other, as well as their net effect on E. huxleyi population dynamics and export in both laboratory and field mesocosm experiments. This integrated approach will provide a unique mechanistic perspective of multi-trophic microbial interactions, thereby increasing the potential for accurate predictions of E. huxleyi population dynamics and biogeochemical cycling. The outcomes of this research have the potential to yield broadly applicable insights into how microbial interactions can drive ecological and biogeochemical dynamics in the marine environment.