Shifting patterns in parrotfish corallivory after 12 years of decline on coral depauperate reefs in the Florida Keys, USA

When coral cover declines, numeric responses of parrotfish can facilitate top-down control of algae and help reefs recover. Yet many parrotfish are facultative corallivores and we know surprisingly little about how their numeric or functional responses to coral decline modify their interactions with coral prey to shape their impacts on surviving corals. Here, we use benthic and fish surveys conducted in the Florida Keys more than a decade apart to assess how coral communities have changed, and how these changes have impacted parrotfish and their predation rates on corals. We found that disturbances and disease have continued to drive declines in coral cover and changes in coral community composition, but that the parrotfish abundance has not changed. In turn, while parrotfish corallivory has remained relatively constant or even declined for some coral taxa, predation on preferred branching Porites species increased 10% in frequency and, when normalized to live tissue area, > 50% in intensity. These coral-mediated shifts in predation correlated with declines in conspecific cover and are indicative of depensatory predation, which can destabilize trophic interactions and drive prey to low densities or even extinction. While coral reefs cannot recover from disturbances without robust parrotfish populations, our study suggests that parrotfish corallivory has important ramifications for coral community structure and, after prolonged degradation, the ability of some diminished coral populations to recover or persist. In a world where corals bleach annually, understanding the functional responses of corallivorous parrotfish to changes in resource abundance will be increasingly important for effective ecosystem-based management.