Effectiveness of different nursery designs for the restoration of the threatened coral Acropora cervicornis in Culebra, Puerto Rico

The threatened staghorn coral Acropora cervicornis is an important reef-builder species in the Caribbean. Its ecological importance and critical status have prompted efforts to restore degraded populations. In this respect, nursery-based programmes have effectively propagated A. cervicornis and helped to increase population sizes. Despite many advances in low-cost coral nursery designs, there is still a need to increase productivity while reducing costs. This study evaluates A. cervicornis demographic performance in two propagation structures: floating trees (FT) and floating horizontal frames (HF). Two equal-sized fragments were collected from 50 healthy staghorn coral colonies. Each fragment was placed into an FT or HF design. Survival, growth, branching, and productivity were recorded for seven months. To address the cost-effectiveness of the coral propagation techniques, we compared the total cost of producing corals between the two designs. Survival was similar, with 91% and 92% of the coral fragments surviving in the FT and HF, respectively. Although colonies in HF nurseries grew faster and produced more branches than those in FT nurseries, these differences were not statistically significant. Likewise, productivity did not differ statistically between nursery designs despite fragments in HF nurseries being 1.5 times more productive than those in FT nurseries. Because of the similarity in demographic performance, the selection of nursery designs could be based solely on their cost-effectiveness. In this respect, the cost-effectiveness analysis shows that producing corals using HF costs about 70% less than FT. Thus, we conclude that floating horizontal frame (HF) nurseries are better for propagating A. cervicornis and accelerating coral restoration activities.