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CANCUN, Mexico (Reuters) - Acidification of the seas linked to climate change could threaten fisheries production and is already causing the fastest shift in ocean chemistry in 65 million years, a U.N. study showed on Thursday.
Production of shellfish, such as mussels, shrimp or lobsters, could be most at risk since they will find it harder to build protective shells, according to the report issued on the sidelines of U.N. climate talks in Mexico.
It could also damage coral reefs, vital as nurseries for many commercial fish stocks.
"Ocean acidification is yet another red flag being raised, carrying planetary health warnings about the uncontrolled growth in greenhouse gas emissions," said Achim Steiner, head of the U.N. Environment Programme (UNEP).
"Whether ocean acidification on its own proves to be a major or a minor challenge to the marine environment and its food chain remains to be seen," he said in a statement.
A UNEP booklet reviewing scientific findings about ocean acidification, caused by water soaking up greenhouse gases from the atmosphere, said that it adds to threats to food security that already include overfishing and pollution.
"It's the speed of change ... that is the cause of concern," said Carol Turley, of the UK Ocean Acidification Research Programme.
"We don't think it has been experienced by the marine environment for 65 million years," when the dinosaurs vanished, she said, presenting a booklet entitled "Environmental consequences of ocean acidification: a threat to food security."
About 25 percent of the world's emissions of carbon dioxide, the main greenhouse gas, are absorbed by the seas, where it converts to carbonic acid. The pH value of the oceans, a scale from alkaline to acidic, has fallen 30 percent since the Industrial Revolution in a shift to acidity.
"We are speaking about a threat especially to the shellfish industry," said Joseph Alcamo, the chief scientist of UNEP. Aquaculture production ranges from French mussels to shrimp in Thailand.
It would also damage coral reefs, and fish that swim around reefs. About a billion people worldwide rely on fish as their main source of protein.
There was evidence that acidification had other effects, for instance impairing the sense of smell of bright-colored clown fish and making it harder for them to avoid predators.
And there were other puzzling findings. Some adult lobsters were apparently increasing shell-building even though juveniles were less able to build healthy skeletons.
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Editing by Todd Eastham