Water circulation and its relation to carbon production are studied in a preliminary investigation on the fringing reef of the Ryukyu Islands. Arrangement of the coral patches on the reef flat reflects the water circulation. The time series of current velocities indicates that water flux is 2.24 × 106 m3 day-1, which is about twice as much as the volume on the reef flat. Tentative biogeochemical studies suggest the net production rate of organic matter and carbonates of the whole reef ecosystem. It appears that about 3% of ΣCO2 in the sea water could be consumed while the water mass moved through Shiraho system.