Corals mass-cultured from eggs and transplanted as juveniles to their native, remote coral reef

Abstract

We attempted to develop practical methods for coral reef rehabilitation, by means of the production of juveniles obtained from sexual reproduction, for a remote island where recruitment is limited. Adult corals (broodstocks) of Acropora tenuis were transported 1100 km from Okinotorishima, Japan's southernmost island in the Pacific, to a hatchery in Okinawa and maintained in land tanks. Eggs were obtained from captive spawning and the resulting larvae and juvenile corals were cultured under laboratory conditions. The present methodology enabled high survivorship and led to the successful mass production of coral juveniles. A total of 564 substrates with ~63 000 juvenile corals at the age of 10 mo were transported to the native reef. They were then transplanted in 3 experimental treatments, in order to evaluate effectiveness of protection by cages and/or hiding the juveniles under other substrates. Additionally, the effects of orientation on coral growth were tested by attaching the juveniles face down. The cages effectively protected the corals from predation and nibbling by fishes. The unshaded, upward facing corals in the cages steadily increased their coverage nearly 4-fold in ~2 yr.

Closing the circle: is it feasible to rehabilitate reefs with sexually propagated corals?

“…Levy et al 2010), however it is in line with costs of other attempts to sexually propagate corals for reef rehabilitation. For example Nakamura et al (2011) estimated costs of approx. US$163 for a single substrate containing numerous 10 month old juvenile corals.…”

“…Large scale sexual propagation of corals for reef rehabilitation has been attempted on relatively few occasions (Omori et al 2008;Nakamura et al 2011). Here we demonstrate the effectiveness of a cheap and easy to make substrate designed specifically for settlement, nursery rearing, and subsequent outplant of sexually propagated corals.…”

“…In recent years, several advances have been made in techniques for sexually propagating broadcast spawning corals specifically for reef rehabilitation (Omori 2005;Okamoto et al 2008;Guest et al 2010;Nakamura et al 2011). Typically, ceramic or terracotta tiles have been used as substrates for settlement of larvae, rearing and transplantation (e.g.…”

“…Typically, ceramic or terracotta tiles have been used as substrates for settlement of larvae, rearing and transplantation (e.g. Omori 2005;Nakamura et al 2011), and this is undoubtedly a legacy of their use in coral larval recruitment studies (Mundy 2000). While square tiles are useful in experiments they are not very suitable as substrates for rearing corals for restoration because (a) it is difficult to control where coral spat settle, (b) tiles are not easy to handle without damaging settled spat, and (c) they do not have a device for specifically attaching them to the reef.…”

The cost and feasibility of marine coastal restoration

“…For oyster reefs, if survival of restored organisms was not reported, it was estimated based on percent cover of oysters on the reef (Konisky et al 2013) or the percentage of successful reefs out of the number of total reefs restored (Powers et al 2009). For the coral reefs records, where only cost per coral colony was provided (Shafir et al 2006, Garrison and Ward 2008, Shaish et al 2008, Ferse 2010, Levy et al 2010, Nakamura et al 2011, Guest et al 2014, calculations for the restoration cost per area were based on a transplanting schedule with four coral colonies out-planted per m 2 or 40 000 coral transplants/ha (Edwards and Gomez 2007). Accounting for a median survival of 64.5% (averaged over the reported pre-transplant, transplant, and post-transplant survival in the coral reef restoration database section), a total of 54 200 coral transplants would be required to populate one hectare.…”