Synchrony patterns reveal different degrees of trophic guild vulnerability after disturbances in a coral reef fish community

Aim Chronic anthropogenic stressors are increasing in intensity, making ecosystems more vulnerable to acute disturbances. Recovery processes are not always well understood due to the complexity of ecosystems and the lack of appropriate indicators. Temporal synchrony is a valuable metric for assessing whether fluctuations in abundance of different species are homogeneous or heterogeneous over time. Theoretically, a great diversity of responses by species facing disturbances is associated with a stable ecosystem, with species turnover guaranteeing the persistence of key ecological processes. We analysed the fluctuations of synchrony of a fish community to assess its resilience in an ecosystem exposed to various disturbances. Location Moorea (French Polynesia). Methods Using one of the longest time series available for coral reefs (ca. 35 years), we examined the variations in substrate cover, and the abundance, synchrony and composition of different fish trophic guilds. Multivariate analyses involving synchrony were used to determine the stability of trophic guilds. Results Changes in fish community composition indicated incomplete taxonomic resilience. However, community synchrony was lower during periods of low coral cover, indicating greater response diversity, while total fish abundance remained fairly stable. Synchrony drop was due to relationships with coral cover that differed by trophic guild, or the differences in species responses within guilds. Some guilds such as sessile invertebrate feeders exhibited a strong homogeneity of response over time, indicating a greater vulnerability. We also highlighted that various types of disturbances had different effects on the synchrony of particular guilds. Main conclusions The fish community appeared functionally resilient, with stability of total abundance and most trophic guilds. This could be a factor explaining the rapid recovery of Moorea's coral reefs from disturbances. However, the homogeneous responses of some fish groups to disturbances may compromise the reef recovery potential on the long term if disturbances become more frequent.