Restoration of heavily denuded reefs is dependent on the recruitment of coral larvae from 'source' reefs where coral populations are capable of producing large numbers of drifting larvae by sexual reproduction. For example, reefs around Okinawa's main island have been seriously damaged in decades, especially in the mass-bleaching event in 1998, and signs of recovery have not been observed yet. Coral larvae are thought to be conveyed from Kerama Islands to Okinawa's main island by the strong current Kuroshio, and this flow pattern was recently confirmed by following slicks (Nadaoka et al., 2001). Reefs around Kerama Islands could act as the source of coral larvae for Okinawa's main island. Nonetheless, few larvae are likely to succeed in traveling 30 km distance through the ocean, even if enormous quantities of gametes were released in mass spawning events. Transportation of slicks through human intervention would be an effective way of enhancing restoration of reefs around Okinawa's main island. Further, if coral larvae collected from slicks were transformed to polyps under controlled conditions, greater successes at coral propagation would be expected than simple transportation of larvae accompanied by low frequencies of settlement and metamorphosis in natural conditions. Controlled induction of metamorphosis will also aid efforts to increase corals within specific reefs, since most of larvae are lost and only a very small fraction of them settle and accomplish metamorphosis in nature.

　

In this study, we demonstrated that the Hym-248 peptide induces metamorphosis in nearly 100% of larvae from slicks (Fig.1). Although this peptide is only effective for acroporids (Iwao et al., 2002), it could be applied to produce polyps from slicks because major mass spawners are acroporids and their larvae dominate slicks (data not shown). Some calcareous algae and marine bacteria can also be used to induce metamorphosis in acroporids (Morse et al., 1996; Negri et al., 2001). However, the efficiency of metamorphosis induction by these organisms is lower and induction takes longer than with the peptide (Fig.2). Another advantage of the peptide is its availability; anyone can obtain peptides by ordering them from reagent companies. In addition, we recently succeeded in culturing over 250,000 larvae from slicks collected in the field in a 1,000 liter-tank till they gain competence of metamorphosis (data not shown). We believe that these results pave the way for 'coral seedlings production', production of a large number of primary polyps as donors for transplantation without damaging existing coral colonies.

　

Coral bleaching events may be becoming more frequent, and it has been suggested that such events will become even more common if global warming persists and summer SSTs increase (Glynn, 1991). Active restoration efforts will become more and more desirable in the future. We hope that this study will be applied to restoration of coral reefs worldwide.

　

　

This study was supported by Yamada Science Foundation and Grants-in-Aid for Scientific Research by the Ministry of Education, Culture, Sports, Science and Technology in Japan.

　

Babcock, R. C., G.D. Bull, P. Harrison, A.J. Heyurard, J.K. Oliver, C.C. Wallace, and B.L. Willis. 1986. Synchronous spawning of 105 scleractinian coral species on the Great Barrier Reef. Mar. Biol. 90:379-394.

　

Glynn, P.W. 1991. Coral reef bleaching in the 1980's and possible connections with global warming. Trend. Ecol. Evol. 6:175-179.

Hayashibara T., K. Shimoike, T. Kimura, S. Hosaka, A. Heyward, P.L. Harrison, K. Kudo and M. Omori. 1993. Patterns of coral spawning at Akajima Island, Okinawa, Japan. Mar. Ecol. Prog. Ser. 101:253-262.

Huppert, A. and L. Stone. 1998. Chaos in the Pacific's coral reef bleaching cycle. Am. Nat. 152:447-459.

Iwao, K., T. Fujisawa and M. Hatta. 2002. A cnidarian neuropeptide of the GLWamide family induces metamorphosis of reef-building corals of the genus Acropora. Coral Reefs 21:127-129.

　

Morse A.N.C., K. Iwao, M. Baba, K. Shimoike, T. Hayashibara and M. Omori. 1996. An ancient chemosensory mechanism brings new life to coral reefs. Biol. Bull. 191:149-154.

　

Nadaoka K., Y. Nihei, K. Wakaki, R. Kumano, S. Kakuma, S. Moromizato, T. Omija, K. Iwao, K. Shimoike, H. Taniguchi, Y, Nakano and T. Ikema. 2001. Regional variation of water temperature around Okinawa coasts and its relationship to offshore thermal environments and coral bleaching. Coral Reefs 20:373-384.

　

Negri A.P., N.S. Webster, R.T. Hill and A.J. Heyward. 2001. Metamorphosis of broadcast spawning corals in response to bacteria isolated from crustose algae. Mar. Ecol. Prog. Ser. 223:121-131.

Takahashi T., Muneoka Y., Lohmann J., Lopez de Halo M. S., Solleder G,, Bosch T. C. G., David C. N., Bode H. R., Koizumi O., Shimizu H., Hatta M., Fujisawa T., and Sugiyama T. 1997. Systematic isolation of peptide signal molecules regulating development in hydra: LWamide and PW families. Proc. Natl. Acad. Sci. 94:1241-1246.

Tsuchiya, M. 1999. Warning from the coral reefs. Galaxia 1:27-29 (In Japanese and English).