Why do coccolithophores calcify? The potential of the calcium carbonate shell to serve as protection against grazers

球石生物是一组全球分布的海洋浮游植物物种，它们被由微小的碳酸钙小片(球石)组成的外壳(球藻)覆盖。通过它们的钙化能力，它们促进了海洋碱度的垂直梯度，加速了有机物向深处的输出，并增加了地球S反照率，使这一功能群成为气候系统中的关键角色。尽管一个多世纪以来对球石生物体钙化及其生物地球化学相关性进行了密集的研究，但最基本的问题之一仍然没有得到解决：为什么球石生物体钙化？回答这个问题非常重要，因为如果我们不能揭示钙化这一关键特征与它们在自然栖息地的成功之间的联系，我们仍然无法预测球石生物在未来海洋中的命运，那里的钙化率被认为是下降的。在这里提出的项目中，我们通过调查球虫是否形成球体来解决这个关键问题，以保护自己免受浮游生物捕食者、传染性细菌和/或病毒的侵害。因此，我们设计了一种新的实验方法，将钙化和去钙化的细胞暴露在不同的食草动物或病原体中。我们的方法将使我们能够解开：(1)钙化的孢子体细胞是否比没有球囊的细胞更能抵御放牧和感染；(2)当提供钙化和去钙化细胞时，食草动物和病原体是否更喜欢没有球球的细胞；(3)当食草动物和病原体以钙化细胞为食或感染钙化细胞时，它们的生长和繁殖是否受到阻碍。

Coccolithophores are a group of globally distributed marine phytoplankton species which cover themselves with a shell (coccosphere) composed of tiny calcium carbonate platelets (coccoliths). Through their ability to calcify they contribute to the vertical gradient in ocean alkalinity, accelerate organic matter export to depth, and increase the Earth s albedo, making this functional group a key player in the climate system. Despite more than a century of intense research on coccolithophore calcification and its biogeochemical relevance, one of the most fundamental questions is still unresolved: Why do coccolithophores calcify? Answering this question is of outstanding importance because if we fail to unravel the link between calcification - the key trait - and their success in the natural habitat we remain unable to predict the fate of coccolithophores in the future ocean where calcification rates are thought to decline. In the project proposed herein we address this key question by investigating whether coccolithophores form the coccosphere to protect themselves against planktonic predators, infectious bacteria, and/or viruses. We therefore designed a novel experimental approach where calcified and de-calcified cells are exposed to different grazers or pathogens. Our approach will allow us to unravel: (1) whether calcified coccolithophore cells better withstand grazing and infection than cells without a coccosphere; (2) whether grazers and pathogens prefer cells without coccosphere when they are offered both, calcified and de-calcified cells: (3) whether the growth and reproduction of grazers and pathogens is impeded when they feed on or infect calcified cells.