Developing coral seeding devices and rapid deployment methods to scale up reef restoration

Current coral restoration methods are constrained by several factors, including low survival rates and high costs of coral production and deployment, making it difficult to address ecosystem‐wide coral declines. This study introduces a new two‐part coral seeding concept to efficiently settle, transport, and deploy coral spat. We then tested this concept, with the aims of (1) identifying characteristics of effective, freely deployed (i.e. unattached) seeding devices, (2) describing suitable deployment locations to maximize the success of coral seeding, and (3) comparing surface versus diver‐deployed device performance. During 6 deployments of 6,400 total devices, we assessed the retention (proportion found), displacement, and yield (i.e. proportion of devices found that had live corals) of 5 alumina ceramic coral seeding device designs to describe the benthic topography where the devices were most successful. After 12–14 months, retention of seeding devices ranged from 62 to 89% and yield ranged from 24 to 60% among deployments. While device shape had minimal influence on the outcome of coral seeding, significant differences in retention and yield were observed among deployment plots. For example, retention was negatively correlated with reef rugosity. Importantly, seeding devices released from the surface demonstrated retention and yield comparable to devices deployed by divers, reducing the cost and increasing the scalability of coral seeding. This study highlights the feasibility of expanding the scale of coral restoration (to hectares) using sexual propagation and coral seeding. However, the success of coral seeding will depend on species selection and characteristics of the receiving sites, including the benthic terrain.