Previous studies have shown that ocean acidification causes some fish to lose their sense of smell, but the new study is the first to demonstrate that it may also affect their hearing.
Juvenile clownfish use hearing to detect and avoid predator-rich coral reefs during the daytime, but new research from the University of Bristol demonstrates that ocean acidification could threaten this crucial behaviour within the next few decades.
Dr Steve Simpson, of the School of Biological Sciences at the University of Bristol, carried out a series of experiments where he reared the larvae of clownfish in different levels of carbon dioxide (CO2) as soon as they hatched.
Several experimental scenarios were designed to reflect current and future ocean acidity, which is expected to increase as seawater absorbs more CO2 from the atmosphere.
Some of the juvenile clownfish were kept in conditions which matched the level of CO2 in today’s oceans, in seawater containing about 390 parts per million (ppm) of CO2.
Three other environments were also simulated based on predictions made by the Intergovernmental Panel on Climate Change (IPCC) for 2050 and 2100, with tanks containing added CO2 to 600, 700 and 900 ppm.
Exposure to daytime reef noise
Dr Simpson then exposed the young clownfish to the sounds of a predator-rich coral reef.
The fish were kept in an ‘experimental choice chamber’ that allowed the researchers to play reef noise through an underwater speaker and watch how the fish responded.
The research team observed that clownfish reared in conditions similar to those in today’s oceans swam away from the noise of predators. However, those clownfish reared in conditions similar to those that may be seen in 2050 and 2100 showed limited or no response, suggesting that they could not hear, could not decipher or did not act on the warning signals.
Potentially devastating effects on fish survival
The ability of fish to adapt to rapidly changing environmental conditions is not yet known.
“What we have done here is to put today’s fish in tomorrow’s environment, and the effects are potentially devastating,” says Dr Simpson. “What we don’t know is whether, in the next few generations, fish can adapt and tolerate ocean acidification.”
Ocean acidification may have profound impacts on the ability of fish to sense and avoid predation. The study demonstrates that CO2-enriched seawater not only affects the external sensory systems of fish, but also those within the body, thereby changing the entire functioning of the sensory system and potentially having a detrimental affect on early survival.
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Helen Roddis, ARKive Species Text Author