"We were rearing larvae under different acidification scenarios and decided to test if elevated CO2/low pH could affect their ability to detect these olfactory cues," Philip Munday of James Cook University, Australia, told environmentalresearchweb. "We had no reason to think it would, but to our surprise we found that the larvae reared in acidified water were no longer able to discriminate between olfactory cues they usually avoided and cues they normally preferred."

Munday and colleagues from James Cook University, Lomonosov State University, Russia, and Norway’s University of Oslo found that larvae reared in seawater with a pH of 7.8 became strongly attracted to scents they normally avoided if reared in more standard seawater with a pH of 8.15. And larvae reared in even more acidic water – pH 7.6 – no longer responded to any olfactory cues.

The scientists believe the effect is due to a disruption of the transfer of chemical signals within the fish’s sensory system, rather than damage to the developing larvae’s sense organs.

To date, studies of the potential effects of ocean acidification have focused on calcifying creatures such as corals, shellfish and some plankton. But almost nothing is known about how acidification could affect other species, such as fish.

"Our research is unique in showing that levels of ocean acidification that could occur by 2100 under a business as usual scenario of carbon emissions can affect the behaviour of marine species," said Munday. "In this case we found that could impair the ability of fish larvae to locate adult habitat at the end of their offshore larval phase. Most benthic marine species have a pelagic [open ocean] larval phase, so the results potentially have important ramification for a broad range of marine species."

Munday believes the results show the importance of curbing carbon emissions. "There could be all sorts of impacts on marine life that we are yet to appreciate," he said. "Certainly our results indicate that proceeding on a business as usual scenario would be detrimental to reef fishes."

The researchers reported their work in PNAS.