The UN Environment Programme said in a report that "land-based pollution, reclamation, clearing of coastal vegetation and poor sewage control can damage reefs."

"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 that had a severe bleaching effect, it said.

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 that 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.

"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.

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, the report said.

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.

Coral reefs, sometimes referred to as "rainforests of the sea," 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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