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

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. 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. 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. 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. 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. Hence, sexual propagation using Acropora is a cost-effective method with relatively high survival and growth that can be used in active restoration.