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[CANCUN, MEXICO] The oceans are acidifying at probably the fastest rate for 65 million years — with unknown implications for the three billion people who depend on fish for protein, a report released at the 2010 UN Climate Change Conference (COP 16), in Mexico has said.

Rising CO2 emissions, a quarter of which eventually dissolve in the oceans to produce carbonic acid, have caused a 30 per cent drop in ocean pH values, reflecting an increase in ocean acidity, according to the report, produced by the UN Environment Programme (UNEP).

"If we go on at the same rate we will have a 120 per cent increase in acidity by the end of the century," said Carol Turley, the report's lead author and knowledge exchange coordinator at the UK Ocean Acidification Research Programme.

The report reviewed scientific literature and found that the effects of acidification on the food chain are still unclear, and more research is needed.

But it outlined many potential threats.

Acidification can reduce the growth and affect the development of smaller fish. For example, it can impair orientation and sense of smell in young clownfish, making them more vulnerable to predators.

A major concern, said the report, is that corals and shellfish may find it harder to form their skeletons, resulting in "significant future impacts on catches of crabs, mussels and other shellfish; species dependent on coral reefs and ones such as salmon that feed on smaller, shell-building organisms lower down the food chain".

Fisheries and aquacultures are an important source of food and income for most of the world's poorer communities, with around a billion depending on fish as their sole source of protein.

"Fish stocks are already under threat from overfishing and habitat loss," said Turley. "I'm sorry to say that we have added another threat to fish, which is acidification."

Tim Kasten, deputy director of UNEP's division of environmental policy implementation, said: "There are some mitigation and adaptation options open to us. The seemingly most obvious one is to rapidly and substantially reduce the amount of CO2 emissions so that we have less entering the marine environment".

Additionally, Kasten suggested looking for marine species that are more flexible to the changing acidity, while working to reduce other stressors such as habitat loss and overfishing.

"Ocean acidification is one of many [stressors] that our marine environments are contending with right now. So how can we reduce some of those other stressors with the knowledge that ocean acidification is not going to go away anytime soon?"

Link to full 'Environmental Consequences of Ocean Acidification: A Threat to Food Security' report