Degradation and restoration of coral reefs: Experience in Okinawa, Japan

Coral reefs in Okinawa, Japan, have declined due mostly to human pressures. There are still possiblities to restore coral reefs locally by amelioration or removal of the local chronic stressors. Political support, scientific information, and the will of local stakeholders are crucial for successful amelioration. Development of techniques for restoration by artificial efforts such as underwater silviculture and transplantation are definitely required. Coral propagules for transplantation may be cultured by either of two approaches: asexual or sexual propagation. The rehabilitation of coral reefs by means of asexual propagation is simple and less labour-intensive compared to sexual techniques. However, most of the transplanted pieces share the donors' limited DNA, giving the reef a smaller gene pool. On the other hand, sexual propagation may result in genetically more diverse corals, but is labour-intensive and more expensive. Both techniques require devices for rearing after transplantation. This will become one of the key areas of research in the near future. Some 4-year-old colonies of Acropora tenuis, cultured from eggs and transplanted to the seabed at Akajima, Okinawa, had grown to 20–25 cm in diameter and initially spawned in June 2009. This indicated the possibility of using this technique to assist local coral reef restoration. Although the small scale of success so far may not be significant, given the wide range of degradation of coral reefs, certain methods of rehabilitation have proved promising enough to continue our endeavour.