For years, images of golden beaches overhung by palm trees have been used to attract tourists to Okinawa, Japan's most southerly prefecture.

Coral reefs teeming with fish and water that is a dazzling turquoise have lured millions to an island that relies heavily on its natural attributes for economic survival.

But the ocean on which it depends is also bringing an invader that threatens to ruin these picture-postcard islands.

"The amount of rubbish that is building up on many of the islands in the Okinawa group is very worrying," said Hareyuki Yamaguchi, a professor at the National Defence Academy.

"I cannot emphasise enough how serious the pollution problem is becoming, and that is a change I have seen in the space of less than 10 years."

For the last decade, the professor has focused his attention on the outlying island of Iriomote, visiting twice a year, in the spring and summer, to conduct research on the scale of the pollution problem.

Unique flora, fauna

And while other islands in Okinawa prefecture - spread over several thousand square kilometres in the Pacific Ocean between Japan, China and Taiwan - are experiencing a similar accumulation of rubbish, Iriomote is causing concern because of its unique flora and fauna.

"The mangrove swamps act as a huge natural barrier and it is impossible to [over] emphasise its importance. But now rubbish is putting this all at risk"

Hareyuki Yamaguchi, National Defence Academy professor

Often referred to as the Galapagos of East Asia, Iriomote is the second largest island in the chain yet has a mere 2000 residents.

More than 90% of the island is tropical jungle, much of which has been designated as a national park by the Japanese government.

As recently as 1965, a new breed of animal was discovered on the island. Experts believe that about 100 Iriomote lynx inhabit the rugged interior, while the crested serpent eagle and yellow-margined box turtle are also listed as protected species.

To some degree, all three of these relatively shy species depend on the mangrove swamps that are interspersed with the beaches around the island and are at greatest risk because of the vast amounts of trash that is being washed up, according to Yamaguchi.

"There are some places where you can hardly put a foot between the rubbish that has washed up," he said.

Foreign origins

"Typically the rubbish that we find falls into several distinct categories: There are the styrofoam buoys, rope, fishing nets, oil drums and plastic sheeting that are from fishing boats; plastic bottles, tin cans, light bulbs and other forms of domestic rubbish - including heavy items such as TVs and refrigerators - and then hospital waste like used syringes and medicine bottles." 

Rope and fishing nets get
deposited on Okinawa's shores

From labels and other marks that his team have been able to identify, about 10% of the trash is Japanese and 30% is Korean.

The remaining 60% bears Chinese characters, meaning it has come from Taiwan, Hong Kong or the Chinese mainland.

The majority of the waste is apparently brought to Okinawa's shores by the Kuroshiro current flowing northwards up the coast of mainland Asia and swirling around the islands of the Japanese archipelago.

In addition, Yamaguchi believes, winds generated over the continent blow offshore during the winter and spring seasons and are followed by powerful typhoons in the late summer that are also able to push debris many hundreds of kilometres.

Affecting ecosystem

And the plastic, steel, paint, styrofoam, nylon and other man-made materials have begun to affect the ecosystem of the islands, he believes. 

"Iriomote's mangrove forests are very important for all the flora and fauna of the island," Yamaguchi said.

"Mangrove leaves fall in the water, are broken down and become the breeding ground for the plankton that are the food for crabs and small fish.

"Those creatures in turn are eaten by larger fish and so on up the food chain. In addition, the soft mud and wetlands are the habitats for these organisms and others, such as snakes, frogs and lizards.

Mangrove swamps are crucial to
the prefecture's ecosystem

"Mangroves are feeding places for larger mammals and birds, while the crustaceans help to filter the water and make it clean again.

"This all works together, naturally, and it is very effective in keeping the water clean and the offshore coral reefs pristine," he said. 

"The mangrove swamps act as a huge natural barrier and it is impossible to [over] emphasise its importance. But now rubbish is putting this all at risk," he added.

Government action

According to Saneo Tamaki, of the Nature Conservation Division of the Okinawa prefectural government, officials are aware of the problem and a dedicated division has been set up to consider ways to combat it.

In recent months, volunteer groups of local residents have held beach clean-up campaigns, although only 50 of the archipelago's 160 islands and smaller reefs are inhabited and those that are more remote are at the mercy of the waves and the waste that they bring. 

"These efforts are obviously important but the clean-up efforts can't keep up with the rate at which the rubbish is being deposited," said Yamaguchi.

"We need to show just how bad the problem is in Okinawa and develop new ways of reversing it as it's a tragedy for nature"

Yamaguchi

"What is more important is to find out exactly where it is coming from and try to stop it arriving in these waters in the first place.

"That is the task of the national government and prefectural governments," he added.

Tourist involvement

"Countries that have coastlines on the East China Sea or the Sea of Japan must hold discussions on how to best protect their oceans as it needs to come from the national level." 

Alternatively, he suggested, the companies that rely on Okinawa as a tourist destination, such as the airlines and large hotel chains, should offer reduced rates for eco-friendly holidays for young people that would combine some days in the sun with expeditions to collect trash from some of the worst affected areas. 

"We need to show just how bad the problem is in Okinawa and develop new ways of reversing it as it's a tragedy for nature," said the professor.

He added that he would continue to seek a way to stop the next wave washing up a rusting oil drum or length of chemical-laden plastic on Okinawa's shores.