Developing Best Practices for the Propagation and Restoration of Massive Corals: The Influence of Predation, Colony Size and Genotype

Coral reefs have undergone drastic declines due to a combination of human and natural disturbances. In response, restoration efforts were developed to recover lost ecosystem services. Over the past decade, reef restoration in Florida has focused almost exclusively on branching Acropora corals but declines in the abundance of corals with massive morphologies highlighted the need to expand our restoration toolbox and develop a holistic “multi-species” approach. Recent studies incorporating corals with massive morphologies into restoration have reported high mortality rates (>50%) because of predation by fish in the first few weeks following outplanting. To address this challenge, I conducted a series of experiments aimed at mitigating predation and understanding factors driving fish predation. I found limiting physical access to newly outplanted corals using colonies of the branching coral Acropora cervicornis, metal spikes, and cages to be highly effective at reducing predation impacts while in place but that cage and spike protective benefits declined immediately after their removal. I identified a size threshold where larger colonies (25 cm2) are less susceptible to predation than smaller coral fragments (5 cm2). I also found coral genotype to play a role in an outplant’s probability of being consumed or removed from the reef by fish, with the most susceptible genotype experiencing 86% mortality after 4 weeks compared to the least susceptible genotype that experienced 26% mortality over the same period. Finally, I found evidence that the observed fish impacts are likely driven by consumption activities and not territorial behavior as dead coral controls were not impacted by fish while adjacent live corals experienced 100% mortality. These results suggest that preventing access by fish to coral outplants by planting them in close proximity to large, complex coral colonies, outplanting larger fragments, and utilizing multiple coral genotypes in restored reefs can be an effective way to limit predation impacts and improve the overall efficiency of reef restoration activities.