酸素・炭素安定同位体比・Mn/Ca比を用いた石垣島轟川河口付近のハマサンゴの壊死研究

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Coral reefs are increasingly faced to the crisis of decline and death caused by climate changes and anthropogenic influence. These crises were reported in Shiraho coral reefs, the Ishigaki Island, Southwestern Japan, caused by the red soils runoff through the Todoroki River. In order to evaluate the influence of terrestrial inputs on coral skeletal growth and coral death, we have analyzed oxygen and carbon isotopic ratios, as well as Mn/Ca ratio, of coral Porites, skeleton collected from Shiraho reef. The coral colony used in this study was still alive but partly dead when the samples were recovered in 20th September 2006. Oxygen isotopic profile of necrosis part indicates that the death may have occurred in winter 2005 when a strongly positive peak of Mn/Ca ratio was observed in the same growth layer of living part, suggesting that increased terrestrial input during sugar cane harvest and closed water system during lower tide level in winter are a possible cause of coral necrosis in the Shiraho coral reefs.
2009-03-30