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 4 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 thousands of kilometers 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. Implications for Practice• When using vessel-based storage facilities for reef restoration, higher quantities of coral embryos can be obtained from pumping wild coral spawn slicks than from transplanted reproductively mature colonies at similar levels of cost-effectiveness. • Harvesting approaches could be implemented on large vessels such as commercial trailer suction hopper dredgers to collect reproductive material from healthy reefs with minimal impact to wild populations and transport them over long distances for deployment onto target reefs in need of rehabilitation at ecologically relevant scales. • Before full-scale efforts are attempted, empirical experiments are necessary to test feasibility and optimize the industrial-scale applications of the coral spawn slick harvesting technology.

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 costefficient, 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.

1. The European native oyster (Ostrea edulis) is a threatened keystone species which historically created extensive, physically complex, biogenic habitats throughout European seas.2. Overfishing and direct habitat destruction, subsequently compounded by pollution, invasive species, disease, predation and climate change have resulted in the functional extinction of native oyster habitat across much of its former range.3. Although oyster reef habitat remains imperilled, active restoration efforts are rapidly gaining momentum. Identifying appropriate sites for habitat restoration is an essential first step in long-term project success.4. In this study, a three-round Delphi process was conducted to determine the most important factors to consider in site selection for European native oyster habitat restoration projects.5. Consensus was reached on a total of 65 factors as being important to consider in site selection for European native oyster habitat restoration projects. In addition to the abiotic factors typically included in habitat suitability models, socio-economic and logistical factors were found to be important. Determining the temporal and spatial variability of threats to native oyster habitat restoration and understanding the biotic factors present at a proposed restoration site also influence the potential for project scale-up and longevity.

Offshore wind is a quickly-emerging market resulting from the worldwide transition towards renewable energies. Whilst this transition has countless environmental benefits, the negative aspects pertaining to underwater noise generated during wind park construction are coming under increased public scrutiny. A number of countries have responded to this environmental and social concern by establishing underwater noise regulations. Construction using current piling techniques often requires the use of underwater noise mitigation systems to meet these legislative requirements. These systems can be applied at the piling source, near pile or far from pile. Under the Underwater Noise Abatement System (UNAS) program, partially sponsored by the Dutch government’s ‘Rijksdienst voor Ondernemend Nederland’ (RVO), a new noise mitigation system has been tested. The UNAS consortium consists of three partners: Van Oord Offshore Wind Projects, AdBm Technologies, and TNO (Netherlands Organization for Applied Scientific Research). The noise mitigation system, here after referred to as NMS, consists of a slatted system containing Helmholtz resonators which is deployed around a monopile in a similar method to venetian blinds. Scaled tests of the NMS at Butendiek and Luchterduinen Offshore Wind Parks showed potential for full-scale deployment. The full-scale test of the NMS was executed in the fall of 2018. A configuration where the vertical spacing of the slats was 0.67 m yielded a 7 to 8 dB SEL re 1 μPa2s reduction compared to the unmitigated scenario, while combining the NMS with a big bubble curtain (BBC) resulted in a 14 to 15 dB SEL reduction compared to the unmitigated situation. This reduction range, as well as a smooth offshore operational performance, puts the NMS in line with other near pile mitigation systems. Deployment of the NMS appears a feasible option to ensure underwater noise compliance in various nation’s legislation.

No abstract