Many coral reefs in the Caribbean are in poor health, having suffered coral losses and increases in macroalgae. Using models, Mumby et al. show that since the mass mortality of a grazing urchin in 1983, Caribbean reefs have shown a general loss of resilience. The reefs are now expected to be highly sensitive to parrot fish exploitation, but this modelling may help identify areas most resilient to both grazing and hurricane damage, with important consequences for reef management.