Reduced extinction risk for autotrophs in the open ocean

The marine plankton record offers a unique archive of deep-time ecological and evolutionary dynamics in the open ocean. With distinct biomineral compositions, trophic modes and other diverse ecological and geographic preferences, fossilized marine unicellular plankton groups (diatoms, calcareous nannofossils/coccolithophores, radiolarians, planktonic foraminifera and dinoflagellates) allow for the identification of traits affecting extinction risk over millions of years. Here, we demonstrate that over the Cenozoic era, trophic mode, classified as either autotrophic, mixotrophic or heterotrophic, is highly influential on the long-term biodiversity dynamics of marine plankton. This trophic distinction is associated with up to a 38% lower Cenozoic extinction rate in autotrophs than in other trophic groups. Correspondingly, autotrophs tend to persist longer and exhibit less volatile extinction dynamics. These patterns hold across multiple levels of comparison: between fully autotrophic and fully heterotrophic groups, within dinoflagellates that include both strategies, and in composite groupings based on trophic mode or biomineral composition. By identifying trophic mode as a key determinant of extinction risk, our results provide a deep-time context for predicting plankton responses to ongoing ocean change.