Marine Biology Research ISSN: 1745-1000 (Print) 1745-1019 (Online) Journal homepage: https://www.tandfonline.com/loi/smar20 Coral restoration research and technical developments: what we have learned so far Makoto Omori To cite this article: Makoto Omori (2019) Coral restoration research and technical developments: what we have learned so far, Marine Biology Research, 15:7, 377-409, DOI: 10.1080/17451000.2019.1662050 To link to this article: https://doi.org/10.1080/17451000.2019.1662050 Published online: 14 Oct 2019. Submit your article to this journal Article views: 357 View related articles View Crossmark data Citing articles: 5 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=smar20 MARINE BIOLOGY RESEARCH 2019, VOL. 15, NO. 7, 377–409 https://doi.org/10.1080/17451000.2019.1662050 REVIEW ARTICLE Coral restoration research and technical developments: what we have learned so far Makoto Omori Akajima Marine Science Laboratory, Zamamison, Okinawa, Japan ABSTRACT ARTICLE HISTORY Coral reef restoration is not the same as forest restoration as its success is not always guaranteed Received 27 July 2018 because of insufficient knowledge of coral biology. The technology of active restoration has a Accepted 2 June 2019 history of only 40 years or less. In spite of many devices and efforts, restoration is often Published online 14 October hampered by low survivorship of colonies, fragments or sexual propagules. In order to 2019 enhance coral resilience and adaptation in a changing world, many new approaches to coral SUBJECT EDITOR ’ reef restoration are being suggested. However, we wouldn t be able to succeed or achieve Naoko Isomura expected result, i.e. recovery and thriving of the coral reefs, if outplanted coral recruits do not grow well and spawn and successfully fertilize in the sea. The cost to restore a few hectares of KEYWORDS reef is often considerable. More studies are needed to improve the methodology. Contractors Coral; coral reefs; restoration; and practitioners of coral reef restoration projects must have advanced techniques supported transplantation; culture by strong science for successful propagation, rearing, and transplantation/outplantation of corals. This review describes what we have learned so far from research on active coral reef restoration and discusses seven topics that may facilitate successful restoration projects. Introduction Under these circumstances, the Coral Reef Targeted Research and Capacity Building for Management Although coral reefs occupy only 0.17% of the world Project for the East Asia and Pacific Region, funded ocean area (Smith 1978), they form habitats for by the Global Environment Facility, was established 830,000 multi-cellular species that account for about (2004–2009). The restoration working group of the 30% of all ocean species (Fisher et al. 2015). Coral project, in which the present author participated, reefs support commercial and recreational fisheries, examined the current state of restoration and rehabili- attract tourism, and protect the coastline from tation techniques and tested various applications. erosion. More than 100 million people live in tropical Results of the studies are summarized in a guideline and sub-tropical coastal areas with coral reefs. Globally, (Edwards and Gomez 2007) and a manual (Edwards the economic net benefit from coral reefs has a value of 2010). All members of the working group agreed to US$30 billion yr−1 (Cesar et al. 2003) and almost US − announce the following in these publications: $350,000 yr 1 for the value of the potential services of an average hectare (De Groot et al. 2012). Although restoration can enhance conservation efforts, However, the effects of global warming and local it is a poor second to the preservation of original habi- anthropogenic disturbances such as pollution and tats. With the present state of technology, we cannot overfishing are subjecting reef corals to severe stresses, create fully functional reefs. Before launching a coral transplantation project, we must remove all possible resulting in intensified bleaching, sedimentation, eutro- stressors of denuded reefs. phication, and disease. Approximately 75% of the world’s coral reefs are rated as threatened when local Under the present circumstances, however, the threats are combined with thermal stress, which reflects traditional (passive) conservation method, with or the impacts of rising sea temperature (Burke et al. 2011; without minimal human input, is not enough to stop see also Carpenter et al. 2008). In spite of various counter- coral reef degradation, and the development of novel measures by administrators, scientists, and the general restoration methodologies is strongly desired (Rinkevich public, significant positive results are lacking. 2008, 2014). CONTACT Makoto Omori [email protected] Akajima Marine Science Laboratory, 179 Aka, Zamamison, Okinawa 901-3311, Japan © 2019 Informa UK Limited, trading as Taylor & Francis Group Published online 14 Oct 2019 378 M. OMORI Reef-building corals (zooxanthellae) reproduce sexu- given that transplantation/outplantaion accounts for ally by internal or external fertilization and asexually only a small component of restoration relative to the by budding or fragmentation. Methods for restoration global scale of coral reef destruction, some scientists and/or rehabilitation of coral reefs are composed of two are still dubious about the effectiveness of active techniques based on sexual and asexual propagation. coral restoration. However, if a large number of coral Direct coral transplantation via asexual propagation, recruits could be transplanted/outplanted successfully, where corals (whole colonies or fragments) are taken they will become ‘spawning hubs’ or ‘spawning hot- from donor communities and relocated to the site to spots’ and produce an increasingly large number of be restored, has been practised since the 1980s larvae each year that will enhance the expansion of (Alcala et al. 1982; Precht 2006). At the beginning of coral reefs (Amar and Rinkevich 2007; Horoszowski- the twenty-first century, when concern over the degra- Fridman et al. 2011; Montoya-Maya et al. 2016; dation of coral reefs was high, restoration techniques Zayasu and Suzuki 2019). were modified to incorporate a nursery phase where Restoration with sexually and asexually propagated small coral fragments, obtained asexually, are grown corals has two phases: (1) propagation and nursery- to sizes suitable for subsequent outplantation (Rinke- farming and (2) transplantation/outplantation. While vich 2006). In addition to the asexual means of propa- the first phase has been developed considerably, the gation, methods of rearing and outplanting of sexually second phase includes many areas that require propagated coral were studied at Akajima Marine further study, such as species and site selection for res- Science Laboratory, Okinawa (Omori et al. 2008; Iwao toration, time and size of recruits to be transplanted/ et al. 2010)(Figure 1). Later, this technique was fol- outplanted, and design to maintain genetic diversity lowed and modified in several studies (Villanueva and species composition (Rinkevich 2014). The con- et al. 2012; Omori and Iwao 2014). dition of corals after transplantation/outplantation Restoration projects are being undertaken at various must be monitored periodically for 3–4 years until places. However, the revival and prosperity of coral they mature and begin spawning. reefs over a large area, indicating a recovery of ecologi- In addition to the literatures mentioned above cal services, has not been verified. Furthermore, even if (Edwards and Gomez 2007; Edwards 2010), there are a restoration project was reported as successful, there several useful manuals and reviews on the coral restor- is no standard goal. Therefore, restoration projects ation (e.g. Edwards and Clark 1999; Omori and Fujiwara are criticized for attempts to save face after a destruc- 2004; Rinkevich 2005). Barton et al. (2017) reviewed tive development project and/or ship-grounding. Also, recent developments in coral propagation. Figure 1. Outplanted Acropora tenuis that was raised from eggs at Akajima Island, Okinawa (5 years old). Courtesy of Akajima Marine Science Laboatory. MARINE BIOLOGY RESEARCH 379 The present paper reviews what we have learned so other causes, for the transplantation. The fragments far from research and projects of active coral restor- in nets or containers are carried by divers or boat ation, and discusses on seven topics that may facilitate without taking them out of the water to the transplan- successful restoration projects. Concluding remarks for tation. The site is cleaned to remove algae and other future coral restoration are presented last. foreign matter by abrasion using wire brush just Note that the author uses the term (coral) restor- before transplantation. Then, the fragments are fas- ation to include both restoration and rehabilitation in tened directly on the seafloor with various ways the present paper. using epoxy putty, masonry nails, stainless wires and cable ties (Okubo 2004). So far, fragments of 2–20 cm long or in diameter have been transplanted. The fol- Techniques using asexual propagation lowings are a review for the ecological and physiologi- So far, most coral restoration studies have used asexual cal results after direct transplantation. propagation techniques using fragments of adult colo- In many cases, the growth rate