ANALYSIS ON MANGROVES DISTRIBUTION CHANGE OVER THE LAST 40 YEARS BY USING RGB IMAGES OF AIRA RIVER MOUTH IN ITIOMOTE ISLAND, JAPAN AND EFFECT BY SEA LEVEL RISE

Abstract

 To analyze the mangroves distribution change in Aira river mouth in Iriomote Island and the effects of sea level rise, the growing ground heights of four mangroves species were measured. As a result of analyzing the tidal observation records in Ishigaki Island, the sea level rise rate was about 2.3 mm/year, and the annual inundation period of the ground height where the tallest mangroves were growing was 3288 hours for A. marina, 2424 hours for S. alba, 2040 hours for R. stylosa, and 1584 hours for B. gymnorhiza. As a result of analyzing the images of Aira river mouth taken in the past, the mangrove forest expanded from 5.24 ha in 1978 to 7.74 ha in 2017, and the R. stylosa forest transitioned to the B. gymnorhiza forest, and the S. alba growing on the tidal flat to the R. stylosa forest. By analyzing the tidal observation records in Ishigaki island and the estimated distribution of mangrove species in Aira river mouth, the sediment accumulation rate of mangrove species in Aira river mouth is about 3.85 mm/year, which is higher than the sea level rise rate of 2.3 mm/year, indicating that the distribution of mangrove species has been expanding.