Ocean Acidification Makes Clownfish Go Deaf (Poor Nemo Can't Hear Predators Anymore...)

Two clownfish in Magnificent Anemone.

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Another Unforeseen Consequence of Global Warming

A clownfish swimming in an anemone on the Great Barrier Reef.

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The planet's oceans absorb a lot of CO2 from the atmosphere, slowly turning them more acidic than they would otherwise be. This can be a big problem for many species that haven't evolved in these conditions, including coral reefs and, scientists have now found, the clownfish (popularized by Pixar's Finding Nemo). Apparently, it's the clownfish's hearing that is most affected by acidification...

What Did You Say?

A clownfish swimming among a pink anemone coral.

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Indeed, researchers found that the clownfish appears to be losing its hearing in water only slightly more acidic than what is normal in the ocean.

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.

But the clownfish in more acidic water showed no preference for moving away from the threatening sound, while those exposed to normal levels of acidity move away from the perceived danger source. This could seriously impact clownfish survival in the long term.

"Avoiding coral reefs during the day is very typical behaviour of fish in open water," said researcher Steve Simpson from the School of Biological Sciences at the UK's Bristol University. Indeed, coral reefs are home to many species that can feed on small clownfish.

"They do this by monitoring the sounds of animals on the reef, most of which are predators to something just a centimetre in length. But sounds are also important for mate detection, pack hunting, foraging - so if any or all of those capacities are gone, you'd have a very lost fish," he told BBC News.

Not Sure Yet What is Causing the Impaired Hearing

Two Clownfish at the Great Barrier Reef, Australia

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The acidity doesn't seem to physically damage the fish's ears, so maybe the damage is neurological, or maybe they are "stressed by the higher acidity and do not behave as they otherwise would."

Look at the Bigger Picture

Clownfish in a coral garden in Asia.

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But the bigger lesson here is that if this happens to clownfish, there are probably all kinds of other hard-to-foresee impacts on other species. We must get CO2 emissions under control and stop ocean acidification before marine ecosystems are more damaged than they already are...