Coral larvae for restoration and research: a large-scale method for rearing Acropora millepora larvae, inducing settlement, and establishing symbiosis.

Eneour Puill-Stephan,Victor H Beltran,Mikhail V Matz,Sarah W Davies,Jeroen A.J.M Van De Water,Margaux Hein,Patrick Buerger,Gergely Torda,David G Bourne,F Joseph Pollock,Bette L Willis,David Abrego,Sefano M Katz

doi:10.7717/peerj.3732

Abstract

Here we describe an efficient and effective technique for rearing sexually-derived coral propagules from spawning through larval settlement and symbiont uptake with minimal impact on natural coral populations. We sought to maximize larval survival while minimizing expense and daily husbandry maintenance by experimentally determining optimized conditions and protocols for gamete fertilization, larval cultivation, induction of larval settlement by crustose coralline algae, and inoculation of newly settled juveniles with their dinoflagellate symbiont Symbiodinium. Larval rearing densities at or below 0.2 larvae mL−1 were found to maximize larval survival and settlement success in culture tanks while minimizing maintenance effort. Induction of larval settlement via the addition of a ground mixture of diverse crustose coralline algae (CCA) is recommended, given the challenging nature of in situ CCA identification and our finding that non settlement-inducing CCA assemblages do not inhibit larval settlement if suitable assemblages are present. Although order of magnitude differences in infectivity were found between common Great Barrier Reef Symbiodinium clades C and D, no significant differences in Symbiodinium uptake were observed between laboratory-cultured and wild-harvested symbionts in each case. The technique presented here for Acropora millepora can be adapted for research and restoration efforts in a wide range of broadcast spawning coral species.

Highlights

Increased intensity and frequency of climate change events combined with increasing local anthropogenic pressures are responsible for alarming declines of coral reefs globally (Gardner et al, 2003; Schutte, Selig & Bruno, 2010; Burke, 2012; De’ath et al, 2012)
We describe a simple and effective method to mass culture coral larvae that can be directly applied for coral research and restoration
Faced with the possibility that corals will be unable to naturally withstand these pressures, researchers and reef managers have begun exploring the utility of active coral restoration (Hein et al, 2017; Rinkevich, 2014)

Summary

Introduction

Increased intensity and frequency of climate change events combined with increasing local anthropogenic pressures are responsible for alarming declines of coral reefs globally (Gardner et al, 2003; Schutte, Selig & Bruno, 2010; Burke, 2012; De’ath et al, 2012). Laboratory-reared coral juveniles provide environmentally responsible and easilyreplicable alternatives to the fragmentation of wild-harvested adult colonies for restoration and research programs (Raymundo & Maypa, 2004; Petersen et al, 2005; Guest et al, 2014; Barton, Willis & Hutson, 2015). The introduction of captive-reared offspring of broadcast-spawning corals onto reefs provides a mechanism to increase genetic diversity, improve early life history survival and introduce resilient genotypes onto damaged reefs (Van Oppen & Gates, 2006; Nakamura et al, 2011; Baria et al, 2012; Guest et al, 2014; Rinkevich, 2014; Van Oppen et al, 2015)

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Discussion

Conclusion