Performance and cost‐effectiveness of sexually produced Acropora granulosa juveniles compared with asexually generated coral fragments in restoring degraded reef areas

Abstract

1. Sexual and asexual modes of coral propagation are used to produce materials to actively restore coral cover on degraded reefs. It is important to evaluate growth, survival and cost-effectiveness prior to any large-scale intervention.2. This study compared the growth, survival and cost of using sexually, compared with asexually, propagated Acropora granulosa at an in situ nursery and, subsequently, on degraded reef patches in the north-western Philippines.3. For sexual propagation, gametes spawned from gravid A. granulosa colonies were collected, fertilized and reared at an outdoor hatchery facility until they were 200-day-old juveniles. For asexual propagation, coral nubbins (obtained from colonies used in the sexual propagation experiment) were reared in the hatchery for 1 month before being transferred to an in situ nursery.4. Sexually and asexually derived corals were reared at the in situ nursery and subsequently out-planted to a degraded reef. Cumulative survival and growth of sexually derived corals were significantly higher than those of the asexually derived ones, both at the in situ nursery (for 200 days) and on coral bommies (for 382 days).At the in situ nursery, mean growth rates were 0.04 and 0.12 cm 3 day −1 for the asexually produced and sexually produced corals, respectively, while those at the bommies were 0.7 and 1.04 cm 3 day −1 , respectively. 5. Production cost (including collection, hatchery-and in situ nursery-rearing) is more expensive in the sexual (US$2.79/coral) than in the asexual (US$2.62/coral) mode of propagation. However, after 13 months post-out-planting it was clear that, in the long run, the individual cost of sexually derived corals is cheaper than the asexual counterparts, US$20.01 vs. US$88.15, respectively, owing to better survival rates.6. Hence, sexual propagation using Acropora is a cost-effective method with relatively high survival and growth that can be used in active restoration. † Deceased

Enhancing Coral Survival on Deployment Devices With Microrefugia

“…Seeding a recruitment-limited reef with deployment devices carrying sexually derived and newly settled coral spat (Okamoto et al, 2008;Chamberland et al, 2015Chamberland et al, , 2017 is one of the interventions being tested and refined (Bay et al, 2019). The benefits of using sexually produced coral propagules in reef restoration include improvements in genetic diversity, scalability and cost (Baria-Rodriguez et al, 2019;Doropoulos et al, 2019;Gibbs et al, 2019;Randall et al, 2020), and if harnessing spawn slicks (Heyward et al, , 2002Doropoulos et al, 2019), retention of species diversity and community composition Doropoulos et al, 2019). Seeding reefs with already-settled coral spat also, at least temporarily, overcomes challenges associated with the settlement process, including a lack of available substrate or settlement cues (Kuffner et al, 2008;Webster et al, 2011Webster et al, , 2013, and the presence of settlement inhibitors (Kuffner et al, 2006;Arnold et al, 2010;Webster et al, 2015;Speare et al, 2019).…”

Using Propagules to Restore Coastal Marine Ecosystems

“…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). Other experiments have variously involved bringing reproductive colonies to a land-based facilities for gamete collection and fertilization, and either settling larvae onto artificial substrates that are then placed onto reefs (Guest et al, 2014;Edwards et al, 2015;Baria-Rodriguez et al, 2019), or directly releasing larvae into mesh enclosures placed on the reefs (de la Cruz and Harrison, 2017). In one experiment, larvae released directly into mesh enclosures grew into reproductive adult colonies (de la Cruz and Harrison, 2017).…”

Enhancing coral recruitment through assisted mass settlement of cultured coral larvae

“…After a few months of hatchery rearing, the juvenile corals on substrata were directly attached to reef sites using adhesive. The same approach was employed by Baria et al [27] where larvae of A. granulosa were settled on artificial substrata in the hatchery and subsequently transplanted to the reef. The cost of each juvenile in the nursery phase was 2.79 USD but increased to 20.01 USD each after transplantation because of additional outplanting costs and subsequent coral mortality [27].…”

“…After a few months of hatchery rearing, the juvenile corals on substrata were directly attached to reef sites using adhesive. The same approach was employed by Baria et al [ 27 ] where larvae of A . granulosa were settled on artificial substrata in the hatchery and subsequently transplanted to the reef.…”

“…granulosa were settled on artificial substrata in the hatchery and subsequently transplanted to the reef. The cost of each juvenile in the nursery phase was 2.79 USD but increased to 20.01 USD each after transplantation because of additional outplanting costs and subsequent coral mortality [ 27 ].…”