Selective feeding by mucous-net filter feeders on the ocean's smallest organisms

海洋表面主要是微小的浮游植物和动物，它们是海洋食物网的基础。被称为附肢动物的果冻状动物专门以这些微型有机体为食，用粘液制成的网过滤大量的水。过去，人们认为阑尾动物吃任何穿过粘液网的东西，但新的研究表明，喂食可能是有选择性的。海洋中最丰富的微生物群体被称为SAR11，它似乎躲避了附属物，而类似大小的光合作用微生物被捕获。在这项研究中，将在美国俄勒冈州和法国苏尔梅尔维尔进行一系列的实验室和田间实验，以揭示选择性的机制。这项研究将测试颗粒形状(例如，球形与椭圆形)的影响、颗粒与粘液网状物的粘附性以及流体力学的作用。它将重点放在世界范围内的附属物Oikopleura dioica，一种重要的微浮游动物食草动物。研究结果对于理解粘液网滤食者在塑造海洋微生物群落结构以及生物地球化学循环中的作用将是重要的。该项目将支持一名职业生涯早期的教员，将为一名博士生和两名本科生提供培训和指导，涉及与法国和以色列的科学家合作，并将通过将在哈特菲尔德海洋科学游客中心和查尔斯顿海洋生物中心展出的展品和图像吸引公众。微小浮游生物的密度高达每毫升100万个，在数量上主导着上层海洋的捕食场。由于附肢动物通过其高过滤速率和粘液聚集体的产生来影响微米和纳米颗粒的通量，选择性放牧将对微生物循环动力学和垂直通量产生重要的影响。因此，这项工作将对控制上层海洋浮游细菌群落结构的机制提供深入的见解，并增加对近海和海洋生态系统中微生物-后生动物食物网相互作用的了解。该项目的具体目标是：a)利用微粒子图像测速仪确定流动形态在调节自由游动附肢动物体内颗粒捕获方面的作用；b)确定颗粒形状对附肢动物滞留效率的影响，并比较合成颗粒和生物颗粒之间的这种影响；以及c)量化颗粒与粘膜过滤装置的粘附性，以确定微浮游动物细胞表面特性是否影响粘液网滤食者的滞留效率。

The surface of the ocean is dominated by microscopic plants and animals called picoplankton, which are at the base of the marine food web. Jelly-like animals called appendicularians specialize in feeding on these miniature organisms by filtering large quantities of water using nets made out of mucus. In the past, it was thought that appendicularians eat anything that passes through the mucous net, but new work shows that feeding may be selective. The most abundant group of microorganisms in the ocean, called SAR 11, seems to evade the appendicularian, while similar-sized photosynthetic microbes are captured. In this study, a series of lab and field experiments will be conducted in Oregon, USA, and Villefranche-sur-mer, France, to uncover the mechanisms for selectivity. The research will test the effect of particle shape (e.g. spherical vs. ellipsoidal), adhesion properties of particles to mucous meshes, and the role of hydrodynamics. It will focus on the cosmopolitan appendicularian Oikopleura dioica, an important grazer of picoplankton. Results will be important for understanding the role of mucous-net filter feeders in shaping the structure of the ocean's microbial community as well as biogeochemical cycling. The project will support an early-career faculty member, will provide training and mentoring for one PhD student and two undergraduates, involves collaboration with scientists in France and Israel, and will engage the public through exhibits and images to be displayed at the Hatfield Marine Science Visitor Center and Charleston Marine Life Center. Picoplankton occur at densities of up to a million per mL and numerically dominate the upper ocean prey field. Since appendicularians influence pico- and nano-particle flux through their high filtration rates and the production of mucous aggregates, selective grazing will have important ramifications for microbial loop dynamics and vertical flux. Therefore, this work will provide insights into the mechanisms governing bacterioplankton community structure in the upper ocean and increase understanding of microbial-metazoan food web interactions in both neritic and oceanic ecosystems. The specific goals of the project are to a) determine the role of flow morphology in regulating particle capture within the houses of free-swimming appendicularians using micro-Particle Image Velocimetry, b) determine the effect of particle shape on retention efficiencies by appendicularians, and compare this effect between synthetic and biological particles, and c) quantify particle adhesion to the mucous filtration apparatus in order to determine if picoplankton cell surface properties influence retention efficiencies by mucous-net filter-feeders.