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9,080,000 Yen (FY1996 2,736,000 Yen)
Since 1970's, catastrophic events such as sedimentation, crown-of-thorns starfish plague and coral bleaching severely affected coral reef ecosystems in Okinawa, Japan. Therefore it is important to assess the health of Scleractinian corals. RNA/DNA ratio is known as an index metabolic intensity of larval fishes, copepod, oyster and so on and has been used to measure nutritional condition. In the present study, we tested whether RNA/DNA ratio can be used as an index of the nutritional status of corals. For the extraction and quantification of nucleic acids of corals, we used the Clemmesen's method with slight modification. We extracted nucleic acids from Galaxea fascicularis with this technique, and confirmed the purity of the nucleic acids using agarose gel electrophoresis. We found that RNA/DNA ratio was positively correlated with tissue dry weight/DNA content in Galaxea fascicularis and Montipora digitata. Tissue dry weight/DNA is considered to reflect nutritional condition of corals, therefore it is also considered RNA/DNA ratio can be used as an nutritional index of corals. We investigated the effect of continuous darkness on RNA/DNA ratio of G. fascicularis. After rearing under continuous darkness for 4 days, RNA/DNA ratio, tissue dry weight/DNA and number of zooxanthellae in the tissue of the corals were statistically lower as compared with the corals reared in an aquarium receiving full sunlight. Under continuous darkness, it is considered that the protein synthesis of the corals is restrained.
Coral, Nutritional Condition, RNA/DNA ratio, Tissue dry Weight/DNA