Survival rates of branching Acropora morphologies on coral rubble stabilization structures

Abstract

Compact bushy and expansive branching Acropora survival rates were compared in an experimental restoration setting. Coral fragments were sourced as corals of opportunity (CoPs) or refragmented from CoPs reared on a floating mid‐water rope nursery. Fragments were attached in single‐species and mixed‐species aggregations to modular substrate stabilization structures (reef stars) on degraded, unconsolidated dead coral rubble slopes in Wakatobi Marine National Park, central Indonesia. In total, 1440 Acropora fragments were outplanted to 96 reef stars across five experimental restoration blocks at 14 m depth. Fragment survival was recorded 40–44 months post‐attachment. Survival had a significant relationship with fragment morphology (p < 0.001) and aggregation type (p < 0.01). Sourcing fragments as CoPs or from the nursery did not have a significant relationship with survival. No significant relationships were found with fragment survival for any interactions between morphology, outplanted aggregation, and source. Survival rates for bushy Acropora were 3.44 times and 5.25 times higher than for expansive species for direct CoP outplants and nursery‐reared corals, respectively. The results demonstrate the potential efficacy of returning complex bushy branching Acropora morphologies to mid‐depth reef slopes previously dominated by the genus, using single‐species aggregations interspersed with mixed‐species aggregations. The study also supports using mid‐water nurseries to create a closed or semi‐closed nursery cycle to scale up restoration, and proposes introducing the term “biomass production system” to distinguish this as a process distinct from other coral nursery approaches.