Corallivorous Fish Have Reduced Population Sizes and Altered Foraging Behaviour on a Recently Restored Coral Reef

Ecosystem restoration is a global priority for biodiversity recovery. However, many restoration efforts to date focus only on planting target species, without evaluating the resulting ecosystem-level impacts on community development and trophic networks. For example, most of the world's efforts to restore tropical coral reefs have evaluated only the recovery of coral organisms. Here, we investigate the re-establishment of different trophic groups of reef fishes in response to rapid coral recovery at one of the world's largest coral restoration projects. Within 4-6 years of coral restoration starting, coral cover returned to levels found at nearby healthy reference sites. Many groups of fishes recovered similarly quickly; herbivores, planktivores and omnivores recovered abundances equivalent to reference sites within the same time frame. However, although corallivorous fish abundance on 4-6-year-old restored reefs was significantly higher than on degraded reefs, it remained at just half the abundance of nearby healthy reference sites. Feeding observations demonstrated that across both healthy and restored habitat, the system's most abundant obligate corallivore (the butterflyfish Chaetodon octofasciatus) consistently targeted a small subset of corals-82% of all recorded bites were on just seven coral morphotaxa. Several of these targeted coral morphotaxa were significantly less abundant on restored reefs than on healthy reference sites. Despite reduced availability of these comparatively rare corals on restored reefs, butterflyfish maintained their dietary preferences, meaning that they exhibited a higher dietary selectivity and foraged over areas twice as large compared to healthy reefs. This demonstrates that despite a rapid recovery of coral cover and some fish groups, the reduced recovery rates of slower-growing coral morphotaxa limit the speed at which specialist corallivores can re-establish. Restored coral reefs may regain their coral cover within 5 years, but they will require longer time frames to achieve full trophic networks and ecological complexity.