Rising CO2 levels leave clownfish deaf to reef noise

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If CO2 levels continue to rise in our oceans, juvenile clownfish are in danger of exposing themselves to predators, by becoming deaf to predator sounds, according to research published in Biology Letters.

Researchers reared larvae of the popular aquarium fish, Amphiprion percula, in water with differing CO2 concentrations for a period of 17-20 days.

Lead author, Dr Steve Simpson of the School of Biological Sciences at the University of Bristol says: "We kept some of the baby clownfish in today's conditions, bubbling in air, and then had three other treatments where we added extra CO2 based on the predictions from the Intergovernmental Panel on Climate Change for 2050 and 2100."

Daytime reef sounds – which consist primarily of the clicks and chirps of crustaceans and fish – were then played to each of the clownfish groups.

"We designed a totally new kind of experimental choice chamber that allowed us to play reef noise through an underwater speaker to fish in the lab, and watch how they responded," Dr Simpson states. "Fish reared in today's conditions swam away from the predator noise, but those reared in the CO2 conditions of 2050 and 2100 showed no response."

Since the Industrial Revolution, over half of all CO2 produced by humans has been absorbed by the ocean, causing the pH to drop faster than any time in the last 650,000 years, resulting in ocean acidification. Studies show that ocean acidification causes negative effects on the sense of smell and this new study demonstrates that acidification may also have an effect on the internal senses of the fish, and possibly the sensory system overall.

However, the ability of fish to adapt to rapidly changing conditions is not known. Dr Simpson said: "What we have done here is to put today's fish in tomorrow's environment, and the effects are potentially devastating. What we don't know is whether, in the next few generations, fish can adapt and tolerate ocean acidification. This is a one-way experiment on a global scale, and predicting the outcomes and interactions is a major challenge for the scientific community."

For further information see the paper: Simpson SD, Munday PL, Wittenrich ML, Manassa R, Dixson D, Gagliano M & HY Yan (in press) Ocean acidification erodes crucial auditory behaviour in a marine fish.

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