The Yomiuri Shimbun 20 Oct 11;
On the famous coral reefs off Ishigakijima island, Okinawa Prefecture, the size of coral colonies has sharply decreased to about a quarter of their size about 10 years ago, according to research by a national environment institute.
The National Institute for Environmental Studies in Tsukuba, Ibaraki Prefecture, an independent administrative institution, conducted the research off the island's Shiraho beach.
The institute believes the decrease is caused by "coral bleaching," a phenomenon in which rising seawater temperatures kill coral; poor behavior by careless tourists who damage coral; and an inflow of red soil erosion into the ocean.
According to the research, the percentage of coral per square meter dropped from 11.9 percent in 1998 to 3.1 percent in 2010.
Some stony corals, known in Japanese as midori-ishi (acropora coral) and komon-sango (montipora coral), are particularly prone to environmental changes, and have decreased drastically to one-hundredth of former levels in some places, according to the institute. Coral bleaching has been observed for more than 10 years. But, red soil erosion from sugarcane and pineapple farms is also contributing to the decrease.
Additionally, the number of tourists visiting the island has increased, rising to about 873,000 last year, or 1.2 times the number from 10 years ago. Many tourists have stepped on or otherwise damaged the coral off Shiraho beach while scuba diving. Ishigakijima island is home to a number of popular diving spots.
