RECRUIT: Recovery of reefs using industrial techniques for coral spawn slick harvesting and release

Accelerating the restoration and recovery of coral populations is a global challenge that has been attempted on many coral reefs around the world. Previous approaches have shown varying levels of success at localised scales, but the comparison of cost and benefits to develop large scale restoration concepts has so far been lacking. Here, we compare two large scale restoration approaches: the harvesting, development, and release of wild coral spawn slicks and the transplantation of fully fecund adult coral colonies. Comparisons incorporate the best available information on the demographic rates to estimate coral population growth beginning at settlement to maturity five years following deployment. Cost effectiveness is also considered in a coarse manner. This contribution elaborates on the apparent optimal approach for large scale application in the current context of the Great Barrier Reef: coral spawn slick harvesting and release. The coral spawn slick harvesting and release approach 27 appears optimal because it achieves large scale restoration of coral communities with low impact technology and at lower cost per colony. Overall, it has the potential to (1) transport billions of thermally tolerant larvae up to 1000s of km’s that (2) are relevant to coral restoration efforts at the geographical scales of the Great Barrier Reef while (3) benefitting from the use of technology that likely has extremely low impact on wild populations and (4) retaining the natural genetic and species diversity needed to enhance the resilience of restored coral communities. The proposed technology and application of using industrial techniques for large scale coral spawn slick harvesting and release is presented. Our contribution also provides valuable insights into critical elements of each concept. We highlight information gaps and the relative sensitivities of different approaches to parameter uncertainties such as levels of larval retention, which could result in different assessments of cost effectiveness.