Reef crises as an Earth-system driver of marine biodiversity loss

Metazoan reefs have experienced repeated crises throughout the Phanerozoic, marked by geologically rapid declines in reef carbonate production. While some of these crises coincided with major biotic turnovers, others left reef-building communities largely intact, and no simple relationship exists between crisis magnitude and ecological change. Consequently, the extent to which reef crises reshaped reef community composition and whether they triggered cascading extinctions among reef-dependent organisms remains unresolved.

Here, we use a global compilation of reef-related fossil occurrences over the Phanerozoic to test whether reef crises affected not only reef builders but also the wider marine biota. We distinguish three cohorts of reef affinity: (i) metazoan reef builders (i.e. colonial corals and sponges), (ii) reef dwellers, and (iii) non-reef organisms. By integrating these data with stage-level changes in reef volume, we evaluate extinction dynamics across four major Phanerozoic reef crises.

We find that reef builders and reef dwellers were tightly coupled over the last 500 million years. Although their background extinction patterns do not indicate simple, one-to-one cascading extinctions, extinction rates in both groups increased significantly during intervals of major reef loss. In contrast, non-reef organisms show no comparable response to reef crises. Our findings highlight the fundamental ecological interdependence between reef-building organisms and the diverse communities they support, and they underscore that the collapse of reef frameworks likely entails the loss of far more biodiversity than reef-building organisms alone.