Abstract
Biodiversity is frequently associated with functional redundancy. Indo‐Pacific coral reefs incorporate some of the most diverse ecosystems on the globe with over 3000 species of fishes recorded from the region. Despite this diversity, we document changes in ecosystem function on coral reefs at regional biogeographical scales as a result of overfishing of just one species, the giant humphead parrotfish ( Bolbometopon muricatum ). Each parrotfish ingests over 5 tonnes of structural reef carbonates per year, almost half being living corals. On relatively unexploited oceanic reefs, total ingestion rates per m 2 balance estimated rates of reef growth. However, human activity and ecosystem disruption are strongly correlated, regardless of local fish biodiversity. The results emphasize the need to consider the functional role of species when formulating management strategies and the potential weakness of the link between biodiversity and ecosystem resilience.