7. Coral Reproduction in Japan

In total, 78 genera and 415 species of zooxanthellate scleractinian corals have been recorded in Japanese waters. The waters of Japan can be broadly divided into three latitudinal regions: the coral reef region (24–30°N, coral reefs with high coral species diversity), the non-coral reef region (30–33°N, coral assemblages with moderate coral species diversity and without coral reef structure), and the peripheral region (33–35°N, undeveloped coral assemblages with low coral species diversity). In this chapter, we review the Japanese and English literatures on coral reproduction in these three regions, focusing upon the timing of spawning and fertilization within and between species. In the cases of Acropora and Montipora, the higher the latitude of a given place, the later the spawning occurs in the year. For example, spawning occurs from May to June in the coral reef region, June to August in the non-coral reef region, and August to September in the peripheral region. The date of spawning seems to be determined in part by water temperature and light intensity that decrease with increasing latitude. Conversely, coral species in the family Merulinidae spawn on similar dates (June to August) in all regions. In addition, several fertilization studies have been performed in Japan to understand the basic mechanisms of fertilization in corals, to identify species boundaries or cryptic species, and to establish efficient seeding techniques. Furthermore, hybridization studies have been conducted to clarify the basis for the high level of Acropora species diversity. Summary of these studies in Japan will contribute largely to understanding coral reproduction on other region in the world.