Science, Tech & Environment

New Dangers for Clownfish

For our Geo Quiz, we're looking for the world's largest coral reef. It's actually made up of about 3,000 smaller reefs and 900 islands, and it stretches over 1,500 miles. It's located in warm waters of the southern hemisphere. The reef is home to an abundance of marine life: starfish and sea turtles, eels and at least a thousand species of fish, including clownfish.

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It was a little, striped clownfish that starred in the animated feature "Finding Nemo."

In the film, Nemo's dad warns his son that the ocean is not safe. In fact the oceans may not be safe for clownfish because of a new threat. The Disney characters live on a reef and our question is, which coral reef is the largest in the world?

Answer: the Great Barrier Reef. It sits along the coast of Northeast Australia in the Coral Sea. If you go diving there you're likely to see clownfish. But clownfish and other marine species may be facing trouble. Carbon dioxide released into the atmosphere from cars and trucks and power plants are making ocean water worldwide more acidic.

A couple of years ago, a scientific study found that ocean acidification may make clownfish lose their sense of smell. Now, a new study say they may lose their hearing, too. Scientists at Bristol University studied young clownfish in a tank in their lab. Some of the fish were reared in normal ocean water, others were reared in more acidic water. Lead researcher Steve Simpson explains how the study worked.

"We had underwater speaker — these are the speakers that are sold for putting in swimming pools but we were playing back the sound of a day-time recording of a coral reef that's rich in predators. So naturally fish would avoid this sound and the fish that we had reared in ambient conditions, today's environment, indeed did avoid that sound. But those who were reared in the CO2 enriched treatments showed no response to the sound," says Simpson.

The fish appeared to be deaf. Simpson says if that's so, it could have devastating consequences. Fish use the sense of sound not only to escape predators but to engage in many behaviors that are key to their survival.

"That could include detecting and finding prey, so foraging behavior: it could affect reproductive behavior; fish use sound to pick their particular mate and to indicate that they're ready to release their eggs and sperm. And so some of the real key behavioural processes that fish use sound for, could be lost".

The new research adds to a growing list of possible threats posed by more acidic oceans. In fact, some of those threats are to coral reefs themselves. They may have a harder time growing in the future. And that means a century from now, Australia's Great Barrier Reef may not be quite as great as it is today.