Recurrent Crown-of-Thorns Starfish ( Acanthaster cf. solaris ) Outbreaks Alter Coral Recovery Trajectories in the Central South China Sea

Tracking the degradation and recovery of foundational organisms is key to understanding ecosystem sustainability. Using coral reefs as a model, we investigated how disturbance frequency affects the recovery of reef-building corals. We examined changes in coral cover, α- and β-taxonomic diversity, functional diversity, and community structure over 3 periods (2006, 2013–2015, and 2022) across 14 sites on 2 atolls in the central South China Sea, where crown-of-thorns starfish outbreaks occurred at different frequencies. Building on 2006 baseline surveys prior to crown-of-thorns starfish-induced decline, our 2013–2015 assessments captured early postoutbreak structural recovery alongside localized degradation associated with thermal stress. Recurrent outbreaks at Yongle Atoll were associated with further community degradation, with communities shifting toward dominance by structurally simpler species. Despite a decline in the overall species and functional composition of communities, β-diversity decomposition revealed that coral communities retained a trend toward functional diversification after repeated outbreaks, meaning that species and functional compositions at individual sites are likely more simplified than anticipated. At Xuande Atoll, which experienced only one major outbreak, coral cover, species richness, and functional diversity at some sites recovered to predisturbance levels within 16 years, despite intermittent thermal stress inhibiting the rate of recovery. However, community structure recovery lags behind, as the delayed recovery of structurally complex groups (e.g., corymbose and table corals) constrains the overall community recovery. Overall, while coral communities can demonstrate recovery potential, repeated disturbances disrupt this process. Therefore, effective conservation must focus on protecting sensitive functional groups and mitigating the frequency of disturbances.