Supporting resilience-based coral reef management using broadscale threshold approaches

Resilience-Based Management of coral reefs aims to maintain ecosystem function and maximise resilience. This requires identification of resilience indicators and clear ecological reference thresholds for reef managers to maintain or aim for. In the absence of local thresholds, managers can assess reef condition by comparing locally collected indicator data to broadscale thresholds, which account for spatial and temporal variability. This study assesses reef condition at Aldabra Atoll, a remote MPA in the western Indian Ocean, relative to broadscale thresholds for structural complexity, fish biomass, herbivore biomass, juvenile coral density, and trophic-level fish biomass. Results were synthesized into a resilience index, and sites were classified into 'management strategies' using a published reef management framework. Resilience scores were then compared to observe coral cover changes following the 2016 bleaching event, tracking recovery through to 2022. Findings showed that seven of the eight assessed seaward reefs at Aldabra displayed the resilience expected of a remote, well-managed marine reserve. The research station and associated human activity appeared to have minimal negative impacts on reef resilience. We recommend expanding the range of broadscale threshold categories and integrating site-specific factors to improve future assessments and management decisions.