"More importantly," it said, "they demonstrate that protection of coastal land area around marine protected areas is essential for reducing local pollution and facilitating re-colonization of corals."

Coral reefs sustained widespread damage in the late 1990s due to higher than normal surface temperatures caused by global warming, it said.

In 1998, temperatures reached as high as 34 degrees Celsius (93 degrees Fahrenheit), severely bleaching reefs worldwide.

Reef recovery is essential to preserving oceanic eco-systems but is jeopardized by rapid coastal development, UNEP said in the report, entitled "Our Precious Coasts: Marine Pollution, Climate Change and Resilience of Coastal Ecosystems."

It found an estimated 70 percent of the world's tropical coasts have been developed and projected that 90 percent would be developed by the year 2030.

The findings, presented at an international marine pollution conference in Beijing and in a statement from UNEP headquarters in Nairobi, were released ahead of a major climate change summit in the Kenyan capital next month.

"Nature can always recover, but the domino effect of bleaching events caused by global warming with pollution has significantly altered the ability of coral reefs to do so," said UNEP Executive Director Achim Steiner.

He urged nations to boost marine protected areas to help corals regrow.

Currently, about 23 percent of reefs worldwide are located in marine protected areas, he said.

Damaged reefs in waters surrounding Mahe, the main island of Seychelles in the Indian Ocean, are recovering at rates ranging from five to 70 percent but those in protected areas are generally recovering faster, according to the report.

In Asia, the removal of mangrove trees to make room for development is polluting coastal waters, where 92 percent of the world's coral is located, the report found.

"Corals are sensitive; they may react to just a few percent of what we consider unhealthy nutrients in water," it said, warning the combination of pollution, sediment and over-fishing may kill some coral entirely.

Coral reefs support over one million plant and animal species and are popular snorkeling destinations.

Sometimes referred to as "rainforests of the sea," they bring an estimated 30 billion dollars (24 billion euros) in revenue to local fishing and tourism industries around the world, the report said.

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