Optimizing growth-out of newly settled sexually-produced corals in land-based nurseries

To increase genetic diversity, coral restoration needs to use sexual reproduction. However, post-settlement mortality of sexually-produced corals in nature and ex situ nurseries is typically high due to macroalgal overgrowth and sensitivity to physical parameters that are optimal for adults, such as light levels. This study aims to optimize the grow-out of sexually-produced corals in land-based nurseries by testing the effect of three easily applicable techniques in large-scale land-based nurseries: cover of corals with coarse sediment to prevent algal overgrowth and provide light protection; shading; and downward orientation. This experiment is being performed in brooders and broadcast spawning coral species. For Porites astreoides, low light levels (20 µmol photons.cm-2s-1) allowed for significantly faster growth and higher coloration during the first 4-5 weeks. After 4-5 weeks, corals grew faster and survived more at higher light levels (180 µmol photons.cm-2s-1). Downward orientation can be used in the first 4-5 weeks to reduce light levels in tanks with light levels more adequate for adult corals. Sediment reduced algal overgrowth, but after 4 weeks it had a negative effect on growth, potentially because it reduced access to food. Results with broadcast spawning species, including Acropora and Orbicella, will be available at the time of the meeting.