Abstract
The largest seagrass bed along the coast of Okinawa Island, southwestern Japan, is located offshore from Henoko and covers 173 ha; the second largest is offshore from Awase and covers 112 ha. Both of these seagrass beds are threatened by the proposed construction of a U.S. military airport and by reclamation. To ensure that the environmental impact assessment compiled before development is fair and correct, an independent scientific survey conducted by citizens should be effective to monitor the development. Given these facts, the Nature Conservation Society of Japan decided to launch a community-based Seagrass-Watch monitoring program called "Okinawa Jangusa-Watch". In this program, volunteers were first trained to identify seagrasses and in the survey method; then, they measured the coverage of each seagrass species by snorkeling at two sites (Kayo and Henoko). After calibrating each observer's error, the distribution and abundance of seagrass were analyzed for each site. Each seagrass species had a specific distribution pattern, based on the distance from the shore. At Henoko, the seagrass coverage determined from the analysis of aerial photos was underestimated, as compared to the coverage measured in the ground survey. A mitigation plan that considers the variation in species composition and seagrass coverage obtained using the ground survey is needed to assess the effects of relocating the U S. military airport. Wide-range, long-term monitoring of seagrass beds by citizens should be effective with regard to monitoring the impact of red soil erosion and global environment change on seagrass beds, and in monitoring specific development projects.
