About a fifth of the colourful marine reefs have already been destroyed and half are threatened with destruction because of the impact of climate change, including increased sea temperatures, according to the IUCN.

New reports by the organisation on coral bleaching and on mangroves showed that attempts to fight other problem areas improve the health of reefs, which are home to about one quarter of known marine species, and make them more resilient to climate change.

"The two reports give a clear positive message: while we cannot stop climate change in the short term, we can help tropical marine ecosystems survive," Carl Gustaf Lundin, head of the IUCN's Global Marine Programme said.

Greater acidity of the oceans, caused by higher levels of dissolved carbon dioxide from emissions, is adding to mass coral bleaching caused by higher sea surface temperatures as well as other forms of pollution, the reports said.

Overfishing also undermines the complex balance of marine life that creates and sustains the reefs, said Gabriel Grimsditch, one of the authors.

Mangroves, which are often directly next to reefs, are part of the same ecosystem, providing a protective nursery for juvenile fish, nutrients for corals and trapping damaging sediments from land, he explained.

Mangroves are threatened by rising sea-levels, more violent tropical storms caused by climate change, as well as clearance during coastal development for tourism or expanding urban areas, the IUCN said.

"We need to minimize human impacts such as pollution, overfishing or unsustainable coastal development," Grimsditch said.

"Then the coral reefs have a bigger chance of coming back after bleaching and of adapting to rising sea temperatures or more acid waters," he added.

Coral reefs provide livelihoods for 100 million people and form the basis for industries such as tourism and fishing, worth 30 billion dollars a year, according to the IUCN.

One hectare of mangroves can deliver products and services worth up to 900,000 dollars in products, including timber and wood chips, and as an environment for fish spawning, it added.

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