The chemistry of the world's oceans is changing at a rate not seen for 65 million years, with far-reaching implications for marine biodiversity and food security, according to a new United Nations study released Thursday.
"Environmental Consequences of Ocean Acidification," published by the U.N. Environmental Program (UNEP)," warns that production of shellfish, such as mussels, shrimp or lobsters, could be most at risk since they will find it harder to build protective shells. It could also damage coral reefs, vital as nurseries for many commercial fish stocks.
Lead author of the report Carol Turley, from the UK's Plymouth Marine Laboratory said in a statement: "We are seeing an overall negative impact from ocean acidification directly on organisms and on some key ecosystems that help provide food for billions. We need to start thinking about the risk to food security."
Tropical reefs provide shelter and food for around a quarter of all known marine fish species, according to the U.N. report, while over one billion people rely on fish as a key source of protein.
Increasing acidification is likely to affect the growth and structural integrity of coral reef, the study says, and coupled with ocean warming could limit the habitats of crabs, mussels and other shellfish with knock-on effects up and down the food chain.
Other marine biologists studying the impact of ocean acidification, which occurs when carbon dioxide dissolves in seawater, have found it affects the ability of fish to smell.
They have discovered that young fish reared in water with elevated levels of carbon dioxide in the water become unable to distinguish the scent of predators and even seem attracted to their smell.
The researchers showed that in the wild, these fish larvae take greater risks, swimming further from shelter that might hide them from predators. More of the fish larvae also die in the wild, sparking fears that fish populations could struggle to survive and replenish themselves as oceans become more acidic.
British researchers pointed out that with an increase in the acidification of the ocean Britain’s famous salmon runs are in danger. The salmon species rely on tiny shellfish when they go out to sea and feed before returning to rivers like the Tay in Scotland or the Test in Hampshire
“One could see a reduction in salmon,” Dr. Carol Turley said. “Ocean acidification may have 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 know as ptetropods.”
The report, unveiled during the latest round of U.N. climate talks in Cancun, Mexico, says that around a quarter of the world's CO2 emissions are currently being absorbed by the oceans, where they are turned into carbonic acid.
Overall, pH levels in seas and oceans worldwide have fallen by an average of 30 percent since the Industrial Revolution. The report predicts that by the end of this century ocean acidity will have increased 150 percent, if emissions continue to rise at the current rate.
But scientists say there may well be winners and losers as acidification doesn't affect all sea creatures in the same way.
Adult lobsters, for example, may increase their shell-building as pH levels fall, as might brittle stars -- a close relation of the starfish -- but at the cost of muscle formation.
"The ability, or inability, to build calcium-based skeletons may not be the only impact of acidification on the health and viability of an organism: brittle stars perhaps being a case in point," Turley said in a statement.
"It is clearly not enough to look at a species. Scientists will need to study all parts of the life-cycle to see whether certain forms are more or less vulnerable."
Scientists are more certain about the fate of photosynthetic organisms such as seagrasses, saying they are likely to benefit from rising acidification and that some creatures will simply adapt to the changing chemistry of the oceans.
The authors identify a range of measures which policymakers need to consider to stop pH levels falling further, including "rapid and substantial cuts" to CO2 emissions as well as assessing the vulnerability of communities which rely on marine resources.
"Ocean acidification is yet another red flag being raised, carrying planetary health warnings about the uncontrolled growth in greenhouse gas emissions. It is a new and emerging piece in the scientific jigsaw puzzle, but one that is triggering rising concern," Achim Steiner, UNEP executive director, said in a statement.
"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 concluded.
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