A Snapshot of the Ecological Contributions of an Active Coral Restoration Effort in an Indo-Pacific Reef

Abstract Active coral restoration is promoted to rebuild reef ecosystems, yet its ecological contributions remain uncertain. We conducted a field experiment across three sites in Nusa Penida Marine Protected Area (MPA): a natural site as the closest reference to the reef’s original state, a rubble site degraded by anthropogenic stressors, and a restoration site (est. 2020) with a monoculture of transplanted Acropora pulchra . We compared benthic cover, fish assemblages, and early succession using ceramic settlement tiles deployed for five durations (6, 8, 10, 12, and 25 weeks). The natural site supported the highest coral cover (40.2% ± 10.96 SE), 47 fishes (19 unique), and commercially important piscivores ( Cephalopholis spp., Lutjanus decussatus , Caranx melampygus ). The rubble site showed low coral cover (13.5% ± 4.53 SE), 32 fishes (9 unique), and detritivore dominance. The restoration site had intermediate coral cover (34.1% ± 11.83 SE) and 40 fishes (16 unique), but no piscivores. Settlement tile experiments revealed coral settler densities (0.028–0.125 cm⁻²) comparable to other Indo-Pacific reefs, but no significant differences among sites. Coral settlement peaked at 10 weeks but declined thereafter, likely due to competition. While crustose algae and other reef binders were abundant, loose rubble likely inhibited substrate consolidation and coral attachment at the rubble site. In both the natural and restoration site, overgrowing phototrophic sponges emerged as a potential threat to corals. Our results suggest that while restoration can enhance habitat structure and fish diversity, trophic rebuilding and long-term coral recruitment may still be limited, highlighting the need for continued monitoring and longer-term assessments. These findings offer insights into restoration potential and ecological conditions in Nusa Penida MPA to enhance reef resilience and management.