Increased dominance of heat-tolerant symbionts creates resilient coral reefs in near-term ocean warming

Global warming is causing the loss of coral reefs worldwide, as a result of heat-induced coral bleaching and mortality. Here, we examined the potential mechanisms that have increased the heat resistance of dominant framework-building coral taxa (Pocillopora spp.) on reefs in the eastern tropical Pacific. We propose that increasing abundance of a thermotolerant symbiotic alga (Durusdinium glynnii) hosted by these corals has facilitated the maintenance of high coral cover after three mass coral bleaching events. This study reveals a mechanism by which some reefs may be more resilient than previously thought and illustrates how future reefs might still maintain high cover for several decades, albeit with low diversity, provided other stressors are minimized.