21-year Changes of Backreef Coral Distribution: Causes and Significance
Keywords:Coral reef, decadal change, aerial photograph, typhoon, Ryukyu Islands
The distribution of corals and their decadal change were observed in Kabira Reef, Ishigaki Island, Southwest Japan. Kabira Reef has distinct topographical and ecological zonation from the shore to the ocean and in addition, ecological zonation along the shore. Coral communities on hard substratum correspond to the current gradient. By analyzing aerial photographs taken in 1973, 1977, 1983, 1986, and 1994, together with the field observations of the change of communities in 1 m- quadrats, an area with marked changes was detected in the moat. The area is composed of fragile branching Montipora digitata on thick bioclastic sediments. Supply of fragments from the upstream zone, the reef pavement, maintains the communities in this zone. Accretion and removal of coral fragments are attributed to the wind direction of typhoons: northern and eastern winds from the ocean to the shore enhance the fragmentation and the expansion of Montipora digitata habitats, whereas southern winds remove the fragments in the moat.