Ecological Response of Plankton to Environmental Change: Thresholds for Extinction

Severe climatic and environmental changes are far more prevalent in Earth history than major extinction events, and the relationship between environmental change and extinction severity has important implications for the outcome of the ongoing anthropogenic extinction event. The response of mineralized marine plankton to environmental change offers an interesting contrast to the overall record of marine biota, which is dominated by benthic invertebrates. Here, we summarize changes in the species diversity of planktic foraminifera and calcareous nannoplankton over the Mesozoic-Cenozoic and that of radiolarians and diatoms over the Cenozoic. We find that, aside from the Triassic-Jurassic and Cretaceous-Paleogene mass extinction events, extinction in the plankton is decoupled from that in the benthos. Extinction in the plankton appears to be driven primarily by major climatic shifts affecting water column stratification, temperature, and, perhaps, chemistry. Changes that strongly affect the benthos, such as acidification and anoxia, have little effect on the plankton or are associated with radiation. Fossilizing marine plankton provide some of the most highly temporally and taxonomically resolved records of biodiversity since the Mesozoic. The record of extinction and origination in the plankton differs from the overall marine biodiversity record in revealing ways. Changes to water column stratification and global circulation are the main drivers of plankton diversity. Anoxia, acidification, and eutrophication (which strongly influence total marine fossil diversity) are less important in the plankton.