Accelerating the recovery of marine coastal ecosystems is a global challenge that has been attempted on many systems around the world. Restoration efforts have shown varying levels of success at localized-scales, but developing techniques for large-scale application are still in their nascent stage for many systems. For seagrass meadows and marsh plants, large-scale successes have been realized by distributing seeds from moving boats or planes, respectively. Similarly for coral reefs, the harvesting, culturing and releasing of wild coral-spawn slicks to targeted reefs is anticipated to achieve cost-efficient, large-scale restoration of coral communities with low-impact technology. Yet, operational protocols for full-scale application still require development by practitioners. In this study we conducted a field trial to evaluate the actual feasibility of harvesting wild coral-spawn slicks for large-scale restoration activities, incorporating technologies used in oil spill remediation, dredging operations, and land-based aquaculture. Testing the potential for scalability to commercial vessels, our trial focused on concentrating and collecting wild coral-spawn slicks for culturing until settlement competency using an experimental 50,000 L aquaculture facility built on a tugboat. Five objectives were set and all were achieved successfully, with only one requiring further optimization. Overall, this restoration approach allows for long-distance translocation of genetically diverse coral assemblages, and may be combined with other larval conditioning techniques that are being developed to increase the resistance to stress and survival of coral recruits. Most importantly, it is fully scalable to produce billions of coral larvae for delivery to target reefs, with negligible impact to source populations.

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Traditionally, marine infrastructure development is regarded to have a negative impact on the ecosystem in or near which it occurs. As a consequence, a whole industry has been treated as a threat and the ingenuity of companies in this industry was forced to focus on minimizing potential negative impacts. Recent trends are to also consider potential positive spin-offs, by including nature-based components in the designs. In this context, Dutch dredging and marine contractor, Van Oord, launched its Coral Rehabilitation Initiative in 2010. A mobile laboratory, named ReefGuard, was developed, to be operated anywhere in the world for sexual reproduction and rearing corals at a large scale (Van Koningsveld et ah, 2017). ReefGuard is used to initiate 'Coral Engines': large scale nurseries with corals obtained through sexual reproduction as well as from fragmentation. These Coral Engines guarantee the long term and large-scale supply of genetically diverse corals for reef creation and rehabilitation. Having coral 'in stock' furthermore allows reefs to be repaired quickly following harmful events such as hurricanes. The involvement of local stakeholders in its setup and operation foresees in sustainable opportunities for research, education and awareness, and local employment. Since 2010 ReefGuard has been applied in five large scale field applications (Australia 2014, 2015, The Bahamas 2015, 2016, 2017) (Van Koningsveld et al, 2017; Robijns et al, 2018; Schutter et al, 2018) producing thousands of sexual recruits consistently. In 2017 a first Coral Engine was delivered with several tens of thousands newly settled coral recruits, and hundreds of one year old recruits and fragments. This paper explains the concept of the Coral Engine in more detail and shares perspectives for future implementation along marine construction projects across the world. Marine infrastructure projects thus become opportunities for coral reef rehabilitation with essential financial and logistical capacity on site, and often also a legislative requirement for compensation of harmful environmental impact.

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Accelerating coral reef restoration is a global challenge that has been attempted around the world. Previous attempts show varying levels of success at localized‐scales, but comparisons of cost and benefits to evaluate large‐scale reef restoration approaches are lacking. Here, we compare two large‐scale restoration approaches: the harvesting, development, and release of wild coral spawn slicks onto a target reef, with the transplantation of gravid coral colonies to provide a seed population and local source of larvae. Comparisons incorporate the best available information on demographic rates to estimate population growth, beginning at embryo production to colony maturity four years following deployment. Cost effectiveness is considered in a coarse manner. The harvesting, development, and controlled release of coral spawn slicks is anticipated to achieve large‐scale restoration of coral communities with low impact technology at low cost per colony. Harvesting wild spawn slicks has the potential to (1) transport billions of larvae up to 1000s of kms that (2) are relevant to coral restoration efforts at vast geographical scales while (3) benefitting from the use of technology with extremely low impact on wild populations and (4) retaining natural genetic and species diversity needed to enhance the resilience of restored communities. Transplanting colonies is most useful from reefs designated to be impacted by infrastructural development by providing an opportunity for transfer to high value zones, from dedicated nurseries, and for brooding species. Our contribution provides insights into critical elements of both concepts, and we highlight information gaps in parameter uncertainties.@en

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. @en