Reversing coral reef decline requires reducing environmental threats while actively restoring reef ecological structure and func-tion. A promising restoration approach uses coral breeding to boost natural recruitment and repopulate reefs with geneticallydiverse coral communities. Recent advances in predicting spawning, capturing spawn, culturing larvae, and rearing settlers haveenabled the successful propagation, settlement, and outplanting of coral offspring in all of the world’s major reef regions. Never-theless, breeding efforts frequently yield low survival, reflecting the type III survivorship curve of corals and poor condition ofmost reefs targeted for restoration. Furthermore, coral breeding programs are still limited in spatial scale and species diversity.Here, we highlight four priority areas for research and cooperative innovation to increase the effectiveness and scale of coralbreeding in restoration: (1) expanding the number of restoration sites and species, (2) improving broodstock selection to maximizethe genetic diversity and adaptive capacity of restored populations, (3) enhancing culture conditions to improve offspring healthbefore and after outplanting, and (4) scaling up infrastructure and technologies for large-scale coral breeding and restoration. Pri-oritizing efforts in these four areas will enable practitioners to address reef decline at relevant ecological scales, re-establish self-sustaining coral populations, and ensure the long-term success of restoration interventions. Overall, we aim to guide the coral res-toration community toward actions and opportunities that can yield rapid technical advances in larval rearing and coral breeding,foster interdisciplinary collaborations, and ultimately achieve the ecological restoration of coral reefs.
The dire state of coral reefs demands a rapid increase in the scale and efficiency of coral restoration methods in addition to mitigating local and global stressors. Larval propagation can provide vast numbers of coral propagules from an individual spawning event and increased genetic diversity in restored populations. The conversion of embryos collected from wild, broadcast-spawning populations to settlers that can be outplanted to the reef is a key component of this production process. We present preliminary results on settlement yield (i.e. % embryos converted to settled polyps on outplantable substrates) following in situ mass culture in floating mesocosms (Coral Rearing In-situ Basins, or CRIBs; 5.6 m3 volume, 5.4 m2 surface area) that can be implemented independent of land-based facilities. Ten trials over 2 years were conducted in three locations using five Caribbean broadcast-spawning species. Embryos were added at different stocking densities and settlement was scored 2–4 weeks after fertilization. Two trials failed, resulting in no effective settlement, but the remaining eight trials resulted in between 1% and 11% settlement yield (overall mean 5.3%) and 77–100% of substrates exposed to larvae acquired settlers (average production: 700 substrates trial−1). Parallel land-based trials showed a similar range (<1–14%) and mean (3.6%) settlement yield over nine trials. These values are also similar to the previously published lab and field-based trials using Pacific Acropora spp. Continued optimization of CRIB design and execution is expected to improve consistency, overall yield, and efficiency in the production of sexual propagules for restoration.