The report, released on Monday, found that these island nations could lose more than half their mangroves by the end of the century.

"The true economic value of ecosystems like mangroves is now starting to emerge," said report coordinator Kitty Simonds.

"Mangroves are important nurseries for fish, act to filter coastal pollution and are important sources of timber and construction materials for local communities," she said.

"Pacific islanders also harvest dyes from mangroves to treat textiles, nets and fish traps."

The report said goods and services generated by mangroves may be worth an average of US$900,000 per square km, depending on their location and uses.

An estimated 75 percent of commercially caught prawns in Australia's tropical state of Queensland depend on mangroves. In Malaysia, a 400 sq km (154 sq miles) managed mangrove forest in Matang supports a fishery worth US$100 million a year.

Mangroves also protect islands from flooding during storms, with mangroves estimated to reduce wave energy by 75 percent, said the report.

For example, mangroves proved crucial in limiting damage to some sections of coast during the 2004 Indian Ocean tsunami.

The report called for a reduction in pollution from land-based sources to make existing mangroves more healthy and resilient to rising seas caused by a warming atmosphere.

Most scientists say burning fossil fuels such as oil, coal and gas is leading to a rapid rise in greenhouse gases that are warming the atmosphere, melting glaciers and causing oceans to expand. Global warming is also expected to lead to more extreme weather, including stronger cyclones in the Pacific.

The report said roughly half the world's mangroves have been lost since 1900 as a result of clearing for development.

"There are many compelling reasons for fighting climate change -- the threats to mangroves in the Pacific underline yet another reason to act," said UNEP executive director Achim Steiner in a statement.