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Coral reefs are tending toward extinction in the world because of coral bleaching, discharge of mud and sand from inland areas, nutrient loads, damage by predators such as starfish, and characteristics of the topography. The coral bleaching event of 1998 was especially strong world wide and was caused by high water temperatures. In Japan's Okinawa Prefecture 80% of all corals were killed. However, in Sekisei lagoon, the largest coral reef region in Japan at 400km/sup 2/ (20km long and 20km wide) the effect was weaker, with about 30% coral mortality. Therefore, Sekisei lagoon can be considered a source of coral supply to Okinawa Island. However, it is not clear how coral eggs and larvae are transported from coral reef regions, such as Sekisei lagoon, to offshore. It is also not clear how coral eggs and larvae released to the offshore waters are transported to other coral reef regions.