Optimizing the Time to Transfer Sexually Produced Corals of Porites astreoides, Agaricia agaricites, and Montastraea cavernosa to an Offshore Nursery

As reefs continue to decline globally and become unable to recover on their own, restoration becomes essential to abate reef degradation and boost reef recovery until the main sources of the degradation are addressed. Sexual propagation is an important restoration technique that still requires optimization. One of the major knowledge gaps is determining the optimal time to transfer newly-settled sexually-produced corals from an aquarium to an offshore nursery without compromising their survival and growth. This study transferred settlers from Porites astreoides, Agaricia agaricites, and Montastraea cavernosa to an offshore nursery at approximately one week, five weeks, and nine weeks post-settlement, with a fourth group always remaining in the aquarium as a control, and found that settlers from all three species could be transferred offshore around 8-12 weeks post-settlement without compromising their survival and growth. At this time, corals were at a stage of development that may have offered many advantages that aided in their survival and growth, such as a fully established community of Symbiodinaceae, grown to a more competitive size, and had hit some developmental milestones. The novel method in which the tiles with the corals were attached to the nursery trees, i.e., the “kebabs”, likely also played a role in their survival. The cost-benefit analysis performed, showed that the longer the corals remained ex situ the more they costed to rear for restoration. Moving corals offshore prior to the 8-12 weeks post-settlement timepoint is possible, and reduces the costs associated with rearing mass amounts of corals but has tradeoffs in survival and growth. Determining the optimal time at which to transfer corals offshore helps restoration practitioners deploy large batches of newly settled corals to an offshore nursery at an age that no longer compromises their survival and growth and may help the settlers to acclimate to local ocean conditions (e.g., acquire beneficial symbionts) from a very early age, potentially making them better suited to their environment