Marine phytoplankton play an important part within the global carbon cylce, removing great amounts of carbon from the atmosphere and producing around half of the oxygen today. Furthermore, forming the largest part of the base of aquatic foodchains, phytoplankton represent the starting point of most biological activities in the oceans. Previous studies have shown the sensitivity of phytoplankton to environmental changes, and their responses to such changes may strongly affect higher trophic levels. Therefore, studying the past diversity of phytoplankton at regional and global scales can provide valuable insights into the evolution of marine ecosystems.
The Palaeozoic diversity curves for marine metazoans are characterised by several global extinction. The impacts on oceanic phytoplankton, however, have been neglected thus far. Based on a comprehensive global database, we reconstructed palaeobiodiversity trajectories of the marine organic-walled phytoplankton (i.e., acritarchs and prasinophytes) in the Palaeozoic and reconstructed origination, extinction and turnover rates. The results show several intervals of significant extinctions, coinciding with important global extinction events for marine metazoans: The most severe happened at the end of the Ordovician, while the Silurian is characterized by repeated minor extinctions. With the Late and end-Devonian extinction event, organic-walled phytoplankton diversity drops relatively slowly but significantly to a prolonged phase of low diversity in the Carboniferous and Permian, also termed the “Late Palaeozoic Phytoplankton Blackout”. Correlations with different palaeoenvironmental parameters are discussed to identify the major controlling mechanisms for Devonian phytoplankton diversity; the data indicate that several factors interacted as the culprit of the severe extinctions in phytoplankton, including short-term climate and sea-level fluctuations. The exact timing of phytoplankton extinction has great implications for the role these organisms play in the large-scale extinction events of the Palaeozoic.
 

phytoplankton,Palaeozoic,Extinction,acritarchs,prasinophytes,primary producers