|Budget Amount *help
¥1,700,000 (Direct Cost : ¥1,700,000)
Fiscal Year 1992 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1991 : ¥300,000 (Direct Cost : ¥300,000)
Fiscal Year 1990 : ¥1,100,000 (Direct Cost : ¥1,100,000)
The distribution, abundance, and composition of rhodoliths are investigated on the basis of 119 grab samples taken around Okinawa-jima, Ryukyu Islands, covering the deep fore reef to island shelf, which ranges in depths from 50 to 200m. The rhodoliths are found from 70 sites at depths shallower than 135m. Coverage of the rhodoliths is about 75% at its maximum, where about 300 rhodoliths larger than 3cm in diameter occur in 1m^2. These rhodoliths are spheroidal, ellipsoidal or rarely disk-like in shape, 50-10cm in mean diameter, and composed of mainly of thin crustose forms of nonarticulated coralline algae and the encrusting foraminifer Acervulina inhaerens, both of which form more or less concentric or irregular internal structure. Bioerosion is frequent, making the rhodoliths porous. Twenty seven species of the nonarticulated coralline algae have been identified, coming under the genera Spongites, Lithoporella, Lithophyllum, Mesophyllum and Lithothamnion. of these genera, Lithothamnion is the most dominant and diverse, reaching 11 species. The nonarticulated coralline algae grow in common to abundance on the surface of the rhodoliths at depths less than 120m, while A.inhaerens predominates at depths exceeding 120m. The presence of a large quantity of rhodoliths on the deep forereef to island shelf mirrors the on-the-spot production of critical amounts of organic and inorganic carbon.
Carbon production of Lithophyllum pallescens, which is luxuriating in the shallow coral reef environment of Ishigaki Island, is mesurerd by alkalinity anomary method. The net organic production / inorganic production ratio of the species is 1/0.9.