Diving survey technique of coral cover as a bio-indicator of environmental changes

Coral is thought of as a sensitive bio-indicator for local and global environmental changes. Also, the coral ecosystem is important as a major producer in the ocean. A monitoring program of coral by satellite has been examined, but as yet has not been realized. Coral is patchily distributed in a small scale compared to a rough satellite eye, and is distributed on the bottom covered with sea water. Even a small change in water depth by tide or wave affects the color spectrum of coral significantly when attempting to observe it from above sea surface. As coral has been studied for long time in from an ecological point of view, distribution of live coral in a broad scale was not of interest. Sekisei Lagoon in Yaeyama Islands was selected as an examination site for monitoring coral from a satellite, and coral coverage at this area was obtained as a ground truth datum. Sekisei lagoon is the largest coral reef area in Japan that is located at 124 degrees E, 240 degrees 20'N, and is 25 x 25km in area Two survey techniques were developed. They were a 50m length diving survey method for minute survey and a cruising survey method for long line rough survey. Using these techniques, 138 diving surveys and 45 cruising surveys were carried out successfully over the entire Sekisei Lagoon between February 1996 and November 1997. Though this data is in the analysis stage, the survey technique, data processing procedure and the data at typical coral reef area are reported.