Testing Industrial-Scale Coral Restoration Techniques: Harvesting and Culturing Wild Coral-Spawn Slicks

Abstract

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.

Priorities and Motivations of Marine Coastal Restoration Research

“…Other examples for biotic motivations are an increase in the number of native species (e.g., for saltmarsh), habitat creation, ecosystem connectivity, and increasing the ecological resilience of the ecosystem (Table S1). Improving the approach to restore coral reefs by harvesting and culturing wild coralspawn slicks to apply at large, industrial scales (Doropoulos et al, 2019) is an experimental (or heuristic) motivation. Building community awareness, involvement, a shared responsibility for the restoration site, and creating jobs through restoration activities is an idealistic motivation for the restoration of coral reefs (Kittinger et al, 2016).…”

Using Propagules to Restore Coastal Marine Ecosystems

“…Demographic modeling suggests that restoration of up to 10 5 adult colonies is feasible by harvesting wild coral-spawn slicks and developing these in large vessels, with minimal impact to wild populations (Doropoulos et al, 2019a). An initial pilot study on the Great Barrier Reef (Australia) yielded 400 times more larvae than predicted by a model (Doropoulos et al, 2019b), due to much greater densities of gametes found in coral spawn-slicks than previously recorded in the literature, and higher survival rates of gametes than anticipated.…”

“…Most coral taxa (63%) are hermaphroditic spawners (Baird et al, 2009). Restoration methods that harness their immense supply of propagules has been conceptualized for decades (Rinkevich, 1995 ; Figures 2e,f) but is challenging in practice because they release gametes only once or twice a year (Babcock et al, 1986), the formation of aggregations of spawn depends on local weather and currents (Oliver and Willis, 1987), and mortality of coral spawn is high (Pollock et al, 2017;Doropoulos et al, 2019b). In some experiments that have sought to overcome these constraints, spawn were collected and reared to larvae in situ in floating ponds; larvae were then pumped directly from these ponds into enclosures attached to the reef or settled onto biologically conditioned artificial substrata such as tiles or aragonite plugs, which are placed onto reefs or back into nurseries for continual production (Heyward et al, 2002;Omori and Iwao, 2014;Omori, 2019).…”

“…Such technology could encompass multiple stages from collection of propagules to rearing them in tanks or nurseries, and finally dispersing them at the site to be restored. For example, large vessels and booms have successfully been used to collect wild coral-spawn slicks and culture them to viable larvae (Doropoulos et al, 2019b), and tank-based techniques have been used to induce settlement of kelp spores onto gravel which is then scattered onto reefs (Fredriksen et al, 2020). Similarly, with tidal marshes the application of mechanized approaches (for seed collection as well as seeding) and processes that concentrate and efficiently store seed can lead to greater efficiencies in the use of propagules when compared to nursery rearing of seedlings and direct planting.…”

Enhancing coral recruitment through assisted mass settlement of cultured coral larvae

“…This approach aims to increase recruitment rates, coral cover [17], and genetic diversity that may improve coral adaptive and evolutionary potential, and increase resilience in depleted coral populations [18][19][20]. Using this approach, millions of sexually derived coral larvae can be sourced from sexually mature coral colonies from ex situ spawning in a controlled hatchery facility [21,22], or in situ by using spawn collectors placed on top of individual corals [23], or from natural coral spawn slicks [24][25][26]. Typically, competent larvae are then settled on artificial substrata and kept in land-or ocean-based nurseries before they are outplanted on the reef [5].…”