Ogasawara Islands:a unique ecosystem..[ 1722 ]

The Ogasawara Islands: Maintaining the balance of a unique ecosystem

The Ogasawara okamono aragai, with its semi-translucent body and small shell.

(Mainichi Japan) August 30, 2010
The Ogasawara Islands, a subprefecture of Tokyo floating in the Pacific, has attracted much attention this year because of the possibility that it may be registered as Japan's fourth Natural World Heritage site in the summer of next year. Believed never to have been contiguous with any other land mass, the Ogasawara Islands have fostered the evolution of unique organisms only found on the islands. However, the islands are rapidly losing diversity. Ahead of the October meeting of the 10th Conference of the Parties (COP10), a U.N. conference that will discuss how to best protect biodiversity, I visited the Ogasawara Islands to see some of the unique creatures there myself.

The light-pink blossom of a Hahajima nobotan.

In July, I climbed 463-meter-tall Mount Chibusa, the tallest peak on the inhabited island Hahajima. Even among the lush nature of the Ogasawara Islands, Mount Chibusa has a particularly large number of unique plants and animals.
Near the top of the mountain, atop the lustrous leaves of Ogasawara Biro palm trees, there was a snail carrying an extremely small shell upon its back. Hideaki Mori, a 29-year-old member of the foundation Japan Wildlife Research Center identified the snail as an Ogasawara okamono aragai. Only about half the size of an adult human's thumb and semi-transparent, I probably wouldn't have ever noticed the snail if it hadn't been pointed out to me. Mori said that the snail only lives in high-humidity areas of Hahajima.

A meguro sparrow, a designated national treasure. It's name means "black eyes."

Other unique species I saw here were wadan no ki, chrysanthemums that have evolved to be almost three meters tall, and Hahajima nobotan, a type of melastome with light pink blossoms. Both grow naturally only in the foggy, high-moisture environment of Hahajima. Additionally, I was able to see the Ogasawara lizard, and the hishikata maimai, a snail. At the foot of the mountain, I found a meguro, a type of sparrow that is black around its eyes and is designated a special natural treasure by the government.
Chichijima, an island with about 2,000 people -- five times the population of Hahajima -- is another island with many unique species. Here, on 302-meter-tall Mount Tsutsuji, a type of azalea called munin tsutsuji grew with white flowers, while a type of buzzard and the only bird-of-prey unique to the Ogasawara Islands, an Ogasawara nosuri, flew the skies. Additionally, on Chichijima, there are estimated to be about 150 of the Ogasawara okomori or the Bonin flying fox, a fruit bat and the only mammal unique to the Ogasawara Islands. The sizable bats have bodies 25 centimeters long and a wingspan of one meter. When the islands were under the control of the army of the United States, the bat was hunted for food and came close to extinction.

An Ogasawara nosuri, a buzzard unique to the Ogasawara Islands.

These islands are sometimes called "evolution's laboratory." Of the plants that grow here, 36 percent are unique to the islands, and of the insects that have been catalogued, 24 percent are unique. A dramatic example is found in land snails, with 114 of the 120 species catalogued here being unique to the islands. While generally not very mobile, it is thought that the snails made it onto the islands thanks to their ancestors being carried by birds from elsewhere. The snails then evolved into new species in response to their environments. The Ogasawara Islands even have a greater number of unique species than the similarly isolated Galapagos Islands of Ecuador, despite the latter having over 70 times the land area. If you compare the number of unique species per unit of area, the Ogasawara Islands have dozens of times more than the Galapagos.
"In the Ogasawara Islands, there are no earthworms or other such competitors in the soil, and there are few natural predators. It's a different environment to what is found on the mainland, and evolution in response to that environment proceeded at a rapid pace," says Satoshi Chiba, associate professor of ecology at Tohoku University.

An Ogasawara okomori, a large fruit bat native to the islands that was nearly hunted to extinction.

Gene analysis has found that the Ogasawara okamono aragai is a descendent of a snail found on the Marquesas Islands, located in French Polynesia. It is unknown when the snail arrived on the Ogasawara Islands, but over a long period, the snail lost much of its shell and evolved into its current form. Chiba infers that, being in a humid environment, the snail no longer had to protect its body from dehydration with a shell. The snail also shows a behavior of hiding in narrow spaces between plants, which may have reduced the need of the shell for protection from predators.
Even now, it seems every year new species are discovered on the Ogasawara Islands. There has even been discovered a species that only lives on the leaves of the agave plant, a foreign species thought to have been introduced since humans settled on the islands 180 years ago. (By Kosuke Hatta, Science and Environment writer)

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