Coral distribution and health at Sekisei Lagoon, Yaeyama Islands
Mineo Okamoto1), Satoshi Kato1) and Satoshi Nojima2)
1) JAMSTEC, 2-15 Natsushima Yokosuka 237-0061, Japan. 2) Amakusa Marine Biological Laboratory, Graduate School of Kyushu University, Japan
Coral is thought as a sensitive bio-indicator for local and global environmental changes. Also, coral ecosystem is important as a big primary producer in the ocean. A monitoring program of coral by satellite has been examined, but it is not realized yet. Coral patchily distributed in a small scale compared to a rough satellite eye, and is distributed at the bottom covered with sea water. Even a small change in water depth by tide or wave affects the color spectrum of coral extremely when observe it above sea surface. As coral has been studied for long time in ecological point of view, distribution of live coral in a broad scale was out of interest. Sekisei Lagoon in Yaeyama Islands was selected as an examination site for monitoring coral from satellite, and coral coverage at this area was obtained as a ground truth data.
Sekisei Lagoon is the largest coral sea area in Japan that locates at 124°E, 24°20'N, 25 x 20 km in width. Two survey techniques were developed. They were 50 m length diving survey method for minute survey and cruising survey method for long line rough survey. Using this technique, 138 diving survey and 45 cruising survey were carried out successfully over whole Sekisei Lagoon between February 1996 and November 1997. By analyzing these data, coral cover around whole Sekisei Lagoon was examined as a basic data. Since 1998, periodical monitoring of coral distribution was started at 10 cruising survey lines and 26 diving survey site. Also, water quality, number of zoo-plankton, chlorophyll etc. were measured around whole Sekisei Lagoon. Additionally, two typical patch reefs (Stations A and C) in 26 were selected for precise monitoring of coral ecosystem. Effect of bleaching event in last summer, recovery of bleached coral, spawning and settlement of larva have been monitored at two Stations. Death rate of corals during bleaching event was estimated within 10% at Sekisei Lagoon. These preliminary data will be presented.
