Drivers of extinction in the marine phytoplankton

海洋浮游植物构成了远洋食物网和生态系统的基础。随着现代人为环境影响——包括富营养化、气候变化和海洋酸化——有证据表明，这一群体已经在经历生物地理范围的变化和群落结构的变化。然而，这一群体中物种灭绝的长期风险却鲜为人知。在这里，我们试图调查大约200万年前一个密切相关的海洋表面栖息藻类群大灭绝期间的动态、原因和群落重组。有关藻类产生碳酸钙（方解石）板状鳞片，这些鳞片在生时由细胞产生并围绕在细胞周围，但在死后会大量积聚在深海沉积物中。这些化石鳞片被称为球粒岩，可以用来重建数百万年来生活在海洋表面的物种的丰富性和多样性。球粒岩的化学成分也可以作为细胞过程和球粒岩形成时海洋表面环境条件的指示物。总之，我们建议利用物种丰度和多样性的变化，以及细胞生长速度和环境的化学指标来确定这种情况下物种灭绝的主要驱动因素。特别是，这主要是由于与其他藻类物种和群体的生物竞争，还是由于海洋表面环境的变化，导致灭绝物种所占据的特定生态位的丧失。了解这一过程，将有助于限制浮游生物灭绝的动态，以及环境压力转化为灭绝风险的机制。

Marine phytoplankton form the basis of pelagic food webs and ecosystems. With modern anthropogenic environmental impacts - including eutrophication, climate change and ocean acidification - there is evidence that this group is already experiencing biogeographic range shifts and changes to community structure. The longer-term risk of species extinction within this group is, however, more poorly understood. Here, we seek to investigate the dynamics, causes and community restructuring during a major extinction of a closely-related group oceanic surface-dwelling alage, approximately 2 million years ago. The alage concerned produce calcium carbonate (calcite) plate-like scales, which are produced by and surround the cell during life, but on death accumulate in great numbers in deep ocean sediments. These fossil scales, called coccoliths, can be used to reconstruct the abundance and diversity of species that were living in the surface ocean across millions of years. The chemistry of coccoliths can also be used as an indicator of cell processes and the conditions in the surface ocean environment at the time the coccoliths were formed. Togther, we propose to use the variations in abundances and diversity of species, as well as chemical indicators of cell growth rates and environment, to determine the main drivers of species extinction in this case. In particular, was this mainly driven by biotic competition with other algal species and groups, or was it due to changing surface ocean environments, which drove the loss of the particular niche occupied by the extinct species. Understanding this process, will help constrain the dynamics of extinction in the plankton, and the mechanisms by which environmental stress is transferred into extinction risk.