Historic coral disturbance versus current coral restoration: insights from Palmyra Atoll

Abstract The utility of passive vs. active coral restoration continues to be debated as reefs decline worldwide. Here, we evaluated the efficacy of coral transplantation into the degraded East and Center lagoons of Palmyra Atoll. Corals have failed to recover in these sites over the eight decades since disturbances associated with World War II, despite high coral cover elsewhere around the atoll that could theoretically provide source propagules. We explicitly compared (i) species beginning to recolonize the lagoons with species common elsewhere at Palmyra, (ii) performance between the East and Center lagoons, and (iii) coral growth at sites near vs. far from causeway inlets as a proxy for the benefits of flow. We found that six common coral species were all physiologically capable of growing in the lagoon, but there were: i) large among-species difference in survival, ii) less, but still significant, differences in growth among species, and iii) localized differences in growth and survival across the eight test locations. Many of these differences appeared to be driven by patterns in fish predation on corals. Survival was greatest for Porites and Pavona species, neither of which have substantially colonized the lagoons. Their superior performance relative to Acropora and Pocillopora species that have begun to recolonize the East Lagoon suggests that transplantation of hardier Porites and Pavona species may accelerate recovery. Coral reef restoration efforts often focus on more threatened and fragile corals like Acropora and Pocillopora . Prioritizing the initial planting of hardier corals like Porites and Pavona may help establish foundational reef functions before introducing more fragile species.