21-year changes of backreef coral distribution: Causes and significance

The distribution of corals and their decadal change were observed in Kabira Reef, Ishigaki island, Southwest Japan. Kabira Reef has distinct topograph ical and ecological zonation from the shore to the ocean and in addition, e cological zonation along the shore. Coral communities on hard substratum co rrespond to the current gradient. By analyzing aerial photographs taken in 1973, 1977, 1983, 1986, and 1994, together with the field observations of t he change of communities in 1 m(2) quadrats, an area with marked changes wa s detected in the moat. The area is composed of fragile branching Montipora digitata on thick bioclastic sediments. Supply of fragments from the upstr eam zone, the reef pavement, maintains the communities in this zone. Accret ion and removal of coral fragments are attributed to the wind direction of typhoons: northern and eastern winds from the ocean to the shore enhance th e fragmentation and the expansion of Montipora digitata habitats, whereas s outhern winds remove the fragments in the moat.