As greenhouse gases build up in the atmosphere and are absorbed by the world’s oceans, the resulting acidification is having a disturbing effect on fish that rely on smell to sense predators.

A team from James Cook University in Queensland, Australia, found that young clownfish reared in acidified water became attracted to the chemical signals released by their predators.

The resulting behavior leads a fish to unwittingly put itself directly in the path of danger, says team leader Danielle Dixson.

The group’s study involved two groups of orange clownfish larvae: some raised in water with roughly the same pH as their natural reef habitat and others raised in more acidic water.

Each group was released into a “flow chamber” in which two parallel water sources were flowing, one drawn from the tanks of the clownfishes’ natural predators and one drawn from tanks in which non-predatory fish were swimming.

"The flow rates are identical, so the water won't mix," Dixson told the BBC. "This allows the fish in the chamber to choose which water cue they prefer or dislike."

The results, which show that fish reared in acidic water were strongly attracted to the predatory stream of water while the other group avoided it, illustrate what could be a growing problem in the world’s oceans.

"Ocean acidification has the potential to become a widespread problem, and it's unknown how many organisms and ecosystems will cope with the decrease [in] pH. This study shows that ocean acidification could lead to an increase in the mortality of larvae."

Ocean acidification causes fatal attraction among fish
Change in pH leads small fish to become attracted to their predators, removing their ability to ‘smell danger’.