Climate change affecting fish hearing

ABC News, 9th March 2007

Marine scientists have found that once fish hatch they use sound to find a home on a coral reef.

But the scientists say warming sea temperatures are affecting the hearing of fish and making them lose their way home.

Dr Steve Simpson from the University of Edinburgh recorded sounds on a reef in Oman and played it to a group recently hatched fish in traps.

He says as coral reef fish move very little after they’ve settled on a reef, finding a good home is crucial to their survival.

“If you’re a centimetre long and you are trying to pick a home, a reef is a pretty dangerous place to arrive at,” Dr Simpson said.

“We’ve described it as having the wall of mouths waiting to receive you. So, you don’t want to get it wrong and have to visit several reefs.

“So, we think that in the same way as say when you are choosing a house, you’d go walking around local areas.

“This gives fish the ability to preview different reefs and make a decision based on those previews. So, they only actually have to take on one wall of mouths.”

Australian fish ecologists then looked at what impact climate change may have on the development of the ear bones on a young reef fish.

Dr Martial Depczynski from the Australian Marine Institute of Science says fish with asymmetrical ears struggle to return to the reef.

“If their hearing is compromised because they have asymmetry, both of their oscillates, or both of their ear bones, are actually a little bit different in size,” Dr Depczynski said.

“If that affects their ability to actually hear, well, it’s going to affect their ability to navigate back to the reef and they’ll just get lost out in the open ocean.”

The research is published in the latest edition of the scientific journal Proceedings of the Royal Society.

It describes how oceans absorb more carbon dioxide due to global warming, changing the pH level of the water and affecting the bone development of fish.

Dr Monica Gagliano from James Cook University says fish are less able to absorb calcium when water is too acidic.

“Fish, like other calcifying organism like corals, need to extract the calcium from the water to be able to build their skeletons, their bones structure, and of course ear bones are made of calcium as well,” Dr Gagliano said.

“And if they can’t extract their proper amount, they might not be able to build those structures properly.”

But Dr Simpson says fish are already affected by other environmental stresses such as underwater noise pollution from shipping, small boat traffic in coral areas plus the sound of drilling and mining.

“We don’t know whether those sounds are scaring fish away from natural habitats or maybe even are attracting them to the wrong habitat,” Dr Simpson said.

“But what they must certainly be doing is producing a lot of background noise that means that then the fish aren’t able to pick out these biological noises that they’re particularly interested in.”

“So, it reduces the range that they can do anything using sound.”

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