Strategies for integrating sexually propagated corals into Caribbean reef restoration: experimental results and considerations

Caribbean hard coral cover has decreased by more than 80% in the last 40 years. In response, active coral restoration has grown in popularity as a management tool to sustain degraded reefs. To date, the majority of coral outplanting has employed asexually propagated ramets derived from wild donor colonies. Unfortunately, this strategy is incapable of increasing genetic diversity and limits the adaptive potential of restored coral populations. Methods for sexual propagation in land-based systems offer increasing potential to enhance genetic diversity of target species. However, questions regarding coral performance once placed back into the dynamic marine environment must be considered. Thus, focused experiments to optimize the integration of land reared corals and novel genetic diversity are of immense value. For this reason, we designed a study using two Acropora cervicornis year classes produced in a land-based system and concurrently relocated to an inshore patch reef, a back reef, and placed in an ocean-based nursery ( n = 80 sexually propagated colonies per location). A deliberate monitoring strategy measured growth and survival five times over a 480-day period. Major findings were 1) high survival rates (~ 73%) across all 160 outplanted colonies 2) significant differences in survival between outplanting locations and coral recruit year class, and 3) very high survival of sexually propagated corals relocated to the ocean-based nursery (~ 93% overall), with 40-fold greater growth than direct-outplanted colonies. Our study suggests that ex situ sexual coral propagation offers a tractable tool to meet the need for increased A. cervicornis genetic diversity. Lastly, we offer insight and considerations for managing the high input of novel genotypes into restoration systems and suggest further research to maximize the adaptive potential of coral populations.