A Trial of Coral Reef Restoration at a Large Spatial Scale 



Okinawa prefecture, Japan


The challenge

Coral reefs in the Okinawa prefecture, Japan, are important habitats supporting high biological diversity and high value fisheries and tourism industries. However, in the early 2000s, coral cover around the Okinawan islands had dropped below 10% due to a range of disturbances including bleaching, predation by Acanthaster cf. solaris, soil erosion, and eutrophication. In 2010, The Okinawan prefectural government declared a “21st century vision for Okinawa” that aimed to review economic and public values of coral reefs and natural coastlines and develop a new system / framework for its conservation and restoration.


Actions taken

The prefectural government conducted a 7-year project (2010-2016) for the technical development and research on coral reef restoration accompanied by various other projects on reef conservation including public awareness and education. The project contained 2 major programs; 1) pilot study of coral outplanting at a large spatial scale, and 2) research on coral reef restoration.

The pilot study of coral outplanting at a large spatial scale was conducted at three locations: Onna, Yomitan and Zamami villages. Activities included:

  • Seed (Juvenile) colony production
  • Growing corals in a nursery
  • Outplanting (at 3 ha)
okinawa kerama

Figure 1. Map of Okinawa Island.


Research on coral restoration included:

  • Reviewing the literature on coral culture and outplanting
  • Conducting genetic analysis of coral populations for genetic diversity
  • Assessing the appropriate density of seed colony for coral outplanting

How successful has it been?

A systematic cycle of seed production and nursery processes was developed for large scale restoration to provide coral seeds across 3 hectares.

  • At Onna village, all coral seeds for outplanting were produced from asexual reproduction from nursed colonies which consisted by 20 Acropora species and 30 other coral species. Coral seeds were also produced by sexual reproduction at private research institutes in Aka Island and Kume Island for outplanting.
  • At Yomitan village, coral seeds were produced at the local facility with asexual reproduction for outplanting.
  • At Zamami village, coral seeds were collected from the natural recruitments on the ropes of the aquaculture facility in the village. The seeds were also produced from the natural larvae during the mass spawning for outplanting.
  • The outplanting area using seeds by asexual reproduction was highest in Onna village with an area of 2.74 ha. The number of seeds were also the highest at the Onna village with 104,687 colonies.
sexual reproduction

Seed production phase: Sexual reproduction. Photo © Okinawa Prefectural Government

asexual reproduction

Seed production phase: Asexual reproduction. Photo © Okinawa Prefectural Government


Nursery phase: Coral seeds with substrate devices. Photo © Okinawa Prefectural Government

031 donor farm

Donor colony farm. Photo © Onna Village Fishery Cooperative


Outplanting at the restoration site. Photo © Okinawa Prefectural Government


For the research phase, current and past information on coral transplantation and restoration were collected to summarize and develop recommendations for future restoration efforts. Genetic analysis of coral populations was also conducted in this project for examining genetic diversity of cultured seed colonies. Finally, the population density of outplanted colonies was assessed to identify appropriate density for successful reproduction.

  • A genomic analysis of the coral Acropora digitifera (Dana, 1846) showed that the species did not have a single gene population in Nansei islands including Okinawa, but there were specific markers at the DNA level for different areas and island localities.
  • Acropora tenuis (Dana, 1846), a popular species for coral restoration, had at least 2 genetic populations in Okinawan waters. However, these 2 populations were not clearly identified, but had different population genetics structures depending on the site.
  • The genetic analysis revealed that the genetic structure of the coral population was complex around Okinawa prefecture and seed colonies and donor colonies for outplanting should be collected from the site near the outplanting to prevent destruction and disturbance of genetic structure of the population. As Acropora tenuis (Dana, 1846) didn’t show any population cloned in its natural habitat, seed colony for restoration should be produced by sexual reproduction. Even when seeds from asexual reproduction were used for outplanting, the donor colonies should be identified on genotypes and seed colonies should be outplanted at the different locations for successful fertilization with different genotypes when they are mature.

Lessons learned and recommendations

The project found 3 major lessons learned:

  1. The cost of seed production is still high and should be reduced for sustainable restoration
    • Seed production by asexual reproduction cost JPY2,000 (US$39) per seed colony compared with JPY2,700 (US$24.82) – JPY3,500 (US$32.18) for seed produced by sexual reproduction.
    • Improving the cost-effectiveness of seed production would require simplifying and optimizing the techniques for both sexual and asexual reproduction, and improving survival after outplanting.
  1. Importance of sustainable system on reef management at the local level
    • Onna village showed successful restoration led by the Fishery Cooperatives during the project. That village has had strong enthusiasm and policy for sustainable development since coral conservation efforts started in 1998 after they experienced mass coral bleaching. The Fisheries cooperative from the village has had many projects to prevent soil erosion, eutrophication and predation of Acanthaster solaris, and protect not only their fisheries resources but also tourist resources. In 2018, the village was declared a “coral village” to respond to another mass coral bleaching event that occurred in 2016, and continue to address challenges of reef conservation for sustainable development. These experiences have accelerated their conservation policy and activities on sustainable use of natural resources and led to long term reef restoration actions.
    • Local community development for sustainable resource management should be emphasized in the context of the reef restoration.
    • Public awareness and education for the community would support long-term and sustainable actions on reef restoration and integrated management along the coast.
  1. Need countermeasures against coral bleaching induced by high water temperatures.
    • Both outplanted and natural coral colonies had severe damages from the mass bleaching in 2016.
    • More research on vulnerable sites, genetic strain of resistance for high water temperature and technical development of shading of natural sunlight would provide possible countermeasures against coral bleaching.

To follow-up on these lessons, a new project is underway until 2022 to tackle the challenges of enhancing seeds’ survival and growth, increasing research on larval dispersal and population dynamics of the outplanted colony, and the effectiveness of ecological, economic and social values, of reef restoration for local communities.


Funding summary

Okinawa prefecture, Japan


Lead organizations

Nature Conservation Division, Department of Environmental Affairs, Okinawa Prefectural Government




This case study was developed in collaboration with the United Nations Environment Programme (UNEP) and the International Coral Reef Initiative (ICRI) as part of the report Coral Reef Restoration as a Strategy to Improve Ecosystem Services: A Guide to Coral Restoration Methods.




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