When is a coral reef recovered? Apparent recovery, structural recovery and the role of disturbance frequency and recovery time

Coral reefs are increasingly exposed to recurrent disturbances such as marine heatwaves, cyclones, and disease outbreaks, which can occur at intervals shorter than the time required for full ecosystem recovery. Reef recovery is commonly assessed using state indicators such as coral cover or biomass, which describe the condition of the system but may not capture changes in ecosystem structure or recovery capacity. As a result, reefs may appear recovered while undergoing long-term structural change. This paper proposes a conceptual framework to distinguish apparent recovery from structural recovery, defined as the recovery of ecosystem structure and recovery capacity. We suggest that reef recovery trajectories may depend on the relationship between disturbance interval (Δt) and structural recovery time (τ). When the interval between disturbances exceeds structural recovery time, structural recovery is possible. When disturbances occur more frequently than structural recovery can be completed, recovery processes may be repeatedly interrupted, leading to cumulative structural change even if state indicators temporarily recover after each disturbance. We propose that the ratio between structural recovery time and disturbance interval (R = τ / Δt) can be interpreted as a time-scale indicator describing whether ecosystems operate under conditions that allow structural recovery, partial recovery, or cumulative structural change. This framework provides a simple way to interpret reef recovery trajectories, resilience, and the risk of long-term structural degradation under increasing disturbance frequency. Understanding reef recovery may therefore require not only measuring ecosystem state, but also evaluating whether ecosystems have sufficient time to recover between disturbances. This time- scale perspective may help explain why some reefs recover after repeated disturbances while others undergo long-term structural change, and may provide a useful conceptual framework for reef conservation and management in a context of increasing disturbance frequency. This framework does not attempt to predict reef dynamics, but to provide a way to interpret why reefs exposed to similar disturbances may exhibit very different recovery trajectories, depending on whether structural recovery processes can be completed between disturbances.