26 January 2006The Yomiuri Shimbun
This is the third installment of Part 1 of a series titled "Environmental Challenges." Part 1 mainly covers problems involving global climate change.
Hiroshi Misaki, director of Kushimoto Marine Park in Kushimotocho, Wakayama Prefecture, laments the huge losses to the coral reef off the Kii Peninsula.
"More than half of the coral has been eaten by crown-of-thorns starfish," Misaki said.
About 120 species of coral live in the waters off the Kushimoto area, which was registered as a Ramsar wetland in November.
Coral reefs, often called "underwater tropical forests," support marine ecosystems with nutritious seaweeds that live inside.
Though located at a relatively high latitude--33 degrees north--the temperature of the water of the reef habitat off the Kushimoto area is nearly 20 C, even in winter, because of the Kuroshio Current that flows nearby.
A large number of crown-of-thorns starfish started to appear in the waters off Kushimoto in 2004. In cooperation with local divers, Misaki has removed more than 30,000 of the creatures, which average 30 centimeters in diameter. On Jan. 17, in just one hour, seven divers caught nearly 500 starfish in waters six to seven meters deep.
Many seas around the globe have been assaulted by armies of crown-of-thorns starfish. There are said to be several causes: rises in water temperature; an overexploitation and a consequent decrease in the number of shellfish that are predators of the starfish; and the depletion of oxygen in the water due to excess plant growth, known as eutrophication.
In Japan, almost all the water surrounding Okinawa Prefecture suffered from an explosion in the number the of starfish in the 1970s. The phenomenon subsided for a while, but has reemerged in recent years.
Before the 1990s, the water temperature off Kushimoto in winter commonly fell below 15 C, making it difficult for tropical creatures to survive.
"At that time, crown-of-thorns starfish soon died when winter came, with only a few appearing," Misaki said.
In recent years, however, the temperature has often stayed over 16 C, even in winter. As a result, 20 species of coral that generally live in warmer parts of the globe have been discovered in the area.
Though the water temperature fell under 15 C last winter for the first time in 15 years, the starfish population did not significantly decline. The starfish had apparently acquired greater resistance to cold temperatures.
In an experiment in which Misaki put a starfish in water with a temperature of 13 C, the creature did not stop eating coral.
A recent drastic increase in the number of Echizen jellyfish, which have caused great damage to fisheries along the Sea of Japan coast, is also said to be the result of rising water temperature.
Scientists agree that the rise in air temperature due to global warming helps raise ocean temperatures.
According to the Meteorological Agency, the average temperature in Japan rose 1.06 C over the 20th century. As a result, compared with 50 years ago, cherry blossoms now bloom five days earlier and leaves start to change color two weeks later on average. The agency predicts the average temperature in the nation will rise another few degrees over the next 100 years.
"The influence of global warming first appears in animals and plants vulnerable to slight temperature changes," said Hideo Harasawa, chief of the National Institute for Environmental Studies' Social and Environmental Systems Division.
According to Harasawa, wild animals and plants move to places that have become more comfortable for them to live. For example, the Great Mormon butterfly, called the Nagasaki Ageha in Japan, whose northern limit of habitat was the Kyushu and Shikoku regions, has recently been observed in the Kanto area.
"In urban areas, the influence of the heat island phenomenon should be taken into consideration," Ryukoku University Prof. Keiko Masuda said.
In Kyoto, an area famous for its beautiful foliage, it was not just that the leaves started to color later than usual last autumn, according to Masuda, many leaves fell even before changing color.
"Global warming will change seasonal landscapes," the Kyoto-based professor said.
Changes have been observed in other parts of the globe. Red foxes on the North American Continent, have started migrating into Arctic areas, threatening the habitat of Arctic foxes.
British researchers have said more than 1 million kinds of terrestrial animals and plants might become extinct by 2050 if global temperatures continue to rise.
The behavior of animals and plants sensitive to changes in their habitats can be a warning signal to humans.
