STUDIES ON CONSERVATION OF LOCAL CORAL COMMUNITIES UNDER THE PROGRESSIVE GREEN HOUSE EFFECT

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1. Recovery of coral communities around Okinawa Island: Recovery processes of coral communities after mass coral bleaching occurred in 1998 were monitored at 10 stations established on coral reefs along mid-west coast of Okinawa Island. Settlement panels for coral larvae were set at each station, and settled corals were examined after collection. Survey of coral communities was also conducted at each station. There were very few mature Acropora colonies, but recruitment of Acropora was large at stations that are located near Kerama Islands. It is suggested that coral populations at Kerama Islands are the source of coral larvae for the recovery of coral communities in Okinawa Island.2. Population genetics of coral populations in the Ryukyu Archipelago: Gene flow of coral populations among Okinawa Is., Kerama Is., and Ishigaki/Iriomote Is. was investigated in eight species of hermatypic corals by allozyme electrophoresis. Laboratory experiments to estimate settlement competency periods of coral larvae were also conducted in three of the eight coral species. The degree of gene flow was similar among the three regions in species having long settlement competency periods (broadcast spawning corals such as Acropora digitifera), but was greater between Okinawa Is. and Kerama Is. than between Okinawa-Kerama and Ishigaki/Iriomote in species having short settlement competency periods (planula brooding corals such as Stylophora pistillata).3. Genotypic diversity of coral symbiotic zooxanthellae among the sites with different coral mortality due to bleaching: Genotypic diversity of symbiotic zooxanthellae in six coral species was compared among three sites that suffered from different degree of coral bleaching in 1998 by DNA analysis using SSCP method. The genotypic diversity of the zooxanthellae was the highest at a site that suffered from the lowest coral mortality due to bleaching, and the lowest at a site that suffered from the highest coral mortality.