Elevated predation on crown-of-thorns starfish in no-take marine reserves

Predator removal can destabilise and devastate ecosystems, particularly if a species released from top-down control can itself fundamentally alter the system¹. On Indo-Pacific reefs, coral-eating crown-of-thorns starfish (CoTS, Acanthaster spp.) threaten ecosystem function and resilience due to their propensity to undergo destructive population outbreaks that cause widespread coral loss^2,3. One of the foremost hypotheses to explain these outbreaks centres around the overfishing of their putative predators^4,5. Notably, outbreaks of CoTS seem to be less prevalent on reefs protected from fishing^4,5, but the risk of predation has never been quantified. Here, we show that the predation risk for CoTS inside no-take marine reserves on Australia's Great Barrier Reef is 3.6- and 2.8-times higher than in areas where fishing is permitted and limited, respectively. Moreover, the elevated predation risk inside no-take reserves is directly attributable to a single fish species, the spangled emperor (Lethrinus nebulosus), a fishery species that shows up to 6.3-times greater biomass on no-take versus fished reefs. These findings may explain how no-take reserves protect reefs from CoTS outbreaks⁴ and highlight targeted conservation of L. nebulosus as a promising management strategy to mitigate reef degradation by CoTS outside of no-take reserves.