Collaborative Research: The Role of Phytoplankton Ballast Material in Deterring Copepod Grazing

许多海洋原生生物（藻类和原生动物）的“装甲”是加厚的细胞壁、鳞片涂层、坚硬的“外壳”（测试、loricas）或格子状的“骨架”。据推测，这些矿床的进化功能是阻止放牧。然而，到目前为止，还没有直接测量原生生物的放牧率作为其矿物质含量的函数。二氧化硅特异性染色的最新发展和最先进的流式细胞术技术使这些测量成为可能。本研究直接检验了桡足类动物的细胞矿物质配额与摄食率之间的关系。在矿物盔甲的相对程度不同的浮游植物细胞将创建使用控制良好的藻类饲养技术。矿物质负荷将通过化学（化学消化）、视觉（扫描电镜）和光度法（矿物和细胞表面特异性染料和流式细胞术）测定。生物矿物所赋予的放牧保护将通过对选择过程背后的行为机制的详细检查（微缩摄影）来研究桡足动物的捕食。初步放牧实验表明，桡足类动物对生物源性矿物质含量低的细胞有强烈的偏好。这表明，高度强化的细胞不太可能被包装成粪便颗粒，从而将浮游生物的矿物质含量从出口到深海的物质中分离出来。这意味着全球生物地球化学循环在一定程度上是由捕食者-猎物相互作用的生态和进化约束构成的。本研究包括测量桡足类动物摄入的颗粒和粪便颗粒的矿物质含量。假设粪便颗粒中较高的矿物质含量会增加颗粒的密度，从而导致更高的沉降速度。生物泵在隔离大气二氧化碳方面的作用部分是由粪便颗粒的快速下沉速度驱动的。本提案中概述的实验将把桡足动物饮食中的矿物质含量与粪便颗粒中的矿物质含量联系起来。随后，直接视频观察将能够测量粪便颗粒的沉降速率作为其矿物质负荷的函数。知识价值：测量和理解控制有机物质流向沉积物的因素一直是许多大型海洋学项目（如JGOFS和ANTARES）的重点。已提出用地表产量或矿物压载物含量的代用物来预测深海通量。然而，如果没有对驱动到达沉积物的物质的质量和数量的潜在过程的机制理解，这些代用物只有在机制保持不变的情况下才是可靠的。桡足类与初级生产者之间的直接相互作用的信息需要预测浮游植物/桡足类联系的变化将如何在有机物向深海的生物泵中表现出来。更广泛的影响：该提案通过在三年的项目中纳入三个学生，为本科教育做出了贡献。该提案有许多独立的子项目，这些子项目将为有动力的本科生提供特殊的机会来获得实际的研究经验。学生将学习不同浮游植物的复杂培养技术，参与放牧实验，学习光学和微缩电影的基础知识。此外，两名学生将以很少的经济成本获得取样和识别浮游生物以及进行放牧实验的宝贵野外经验。我们实验室的学生将被要求每周开会讨论问题，最近的成功，以及与他们特定主题相关的文献。鼓励学生参加专业社团的会议和活动。该项目的成果还将有助于Bigelow实验室教育和推广计划的发展，最值得注意的是Phytopia项目及其为中学和大学学生和教师提供的相关实用工具（http://www.bigelow.org/phytopia/）。

Many groups of marine protists (algae and protozoa) are "armored" with thickened cell walls, coatings of scales, hard "cases" (tests, loricas), or latticework "skeletons". The inferred evolutionary function of these mineral deposits is to deter grazing. However, to date there are no direct measurements of grazing rates on protists as a function of their mineral content. The recent development of silica specific stains and state of the art flow cytometry techniques enable these measurements. This study directly tests the relationship between the cellular mineral quota and the ingestion rates of copepods. Phytoplankton cells that differ in the relative degree of mineral armor will be created using well controlled algal rearing techniques. Mineral load will be determined chemically (chemical digestion), visually (SEM), and photometrically (mineral and cell surface specific dyes and flow cytometry). The grazing protection conferred by biogenic minerals will be examined against copepod predation with detailed examination (microcinematography) of the behavioral mechanisms that underlie the selective process.Preliminary grazing experiments show that copepods have a strong preference for cells with low biogenic mineral content. This suggests that heavily fortified cells are less likely to be packaged into fecal pellets, thus uncoupling the mineral content of plankton from what is exported to the deep ocean. This implies that global biogeochemical cycles are structured, in part, by the ecological and evolutionary constraints of predator-prey interactions. This study includes measurement of the mineral content of the ingested particles and of the fecal pellets of copepods. The hypothesis is that a higher mineral content in the fecal pellet will increase the density of the pellet and therefore, lead to a higher settling velocity. The role of the biological pump in sequestering atmospheric CO2 is driven, in part, by the rapid sinking rates of fecal pellets. Experiments outlined in this proposal will link the mineral content of the copepod diet with the mineral content of the fecal pellet. Subsequently, direct video observations will enable measurement of the sinking rates of fecal pellets as a function of their mineral load.Intellectual Merit: Measuring and understanding the factors that control the flux of organic material to the sediments has been the focus of numerous large oceanographic programs (e.g. JGOFS and ANTARES). Proxies of surface production or mineral ballast content have been proposed to predict deep ocean fluxes. However without a mechanistic understanding of the underlying processes driving the quality and quantity of material reaching the sediments, these proxies are robust only when the mechanisms remain constant. Information on the direct interactions between copepods and primary producers is needed to predict how changes in the phytoplankton/copepod link will manifest in the biological pump of organic matter to the deep ocean.Broader Impacts: The proposal contributes to undergraduate education by incorporating three students during the three year project. The proposal has numerous self-contained sub-projects that will provide exceptional opportunities for motivated undergraduate students to receive hands on research experience. Students will learn sophisticated culturing techniques for different phytoplankton, participate in grazing experiments and learn the fundamentals of optics and microcinematography. In addition, at little financial cost to this proposal two students will gain valuable field experience in sampling and identifying plankton and conducting grazing experiment. Students in our lab will be required to meet weekly to discuss problems, recent success, and pertinent literature to their specific topic. Student participation at meetings and activities of professional societies will be encouraged. Results of the project will also contribute to the development of Bigelow Laboratory educational and outreach programs, most notably the Phytopia project and its allied utilities for learners and teachers at secondary and tertiary levels (http://www.bigelow.org/phytopia/).