Clownfish, the spectacular tropical species feted in the movie Finding Nemo, appear to lose their hearing in water slightly more acidic than normal.
At levels of acidity that may be common by the end of the century, the fish did not respond to the sounds of predators.
In this experiment, the fish could decide whether to swim towards or away from an underwater loudspeaker replaying the sounds of predators recorded on a reef, with shrimps and fish that would take a small clownfish.
In water with today’s levels of CO2, the fish spent three-quarters of the time at the opposite end of the tube from the loudspeaker. But at higher concentrations, they showed no preference.
This suggests they could not hear, could not decipher or did not act on the warning signals.
If it takes several decades for the oceans to reach these more acidic levels, there is a chance, the team says, that fish could adapt.
There appears to be no physical damage to their ears; the team suggests there could be some effect on nerves, or maybe they are stressed by the higher acidity and do not behave as they otherwise would.