By Isabel Dayman

Baby fish may lose their ability to find their way home in the future due to rising CO2 levels in the ocean, a marine ecology expert has found.

University of Adelaide Professor Ivan Nagelkerken said some species of fish larvae relied on sounds in the ocean to find their way between open areas and shallow water.

When larvae grow big enough, they find their way to their natural habitats along the coastlines.

“A lot of larvae have evolved to use certain cues to help them find their new homes … including sounds,” Professor Nagelkerken said.

“It’s a very reliable, directional cue that can help them to navigate to find these homes.”

All the wrong noises

Coastal areas are actually very loud if you are an underwater creature.

“They harbour a lot of snapping shrimp and a lot of animals that can produce sounds, and sound can travel a long way in water,” Professor Nagelkerken said.

What the study found was that fish larvae were not paying attention to the right noises.

The research compared the behaviour of barramundi larvae in normal water to water with elevated CO2 levels similar to those predicted for the end of the century.

The right sounds would have led the barramundi to their natural habitat — tropical estuarine mangroves.

Instead, they were attracted to different sounds and white noise, leading them to habitats that were not beneficial to their survival.

Consequences could be devastating

Professor Nagelkerken said the results indicated rising CO2 levels disrupted the ability of larvae to use sound as a guiding tool when moving around the ocean at critical life stages.

“When we raised these larvae under elevated CO2, we saw that those larvae were no longer attracted — and worse, they were deterred by — the natural sounds of their natural habitat,” he said.

“Lower pH levels, acidity levels or higher CO2 levels interfere with the neurotransmitter function in their brain, and as a result, normal behaviours are being altered.”

And that will have devastating consequences because there will be no “recruitment”, or returning larvae, Professor Nagelkerken explained.

External Link:

Lost at sea: the effect of ocean acidification on fish behaviour

He said the findings held concerning implications for fish populations in the future if species failed to adapt to elevated levels of CO2.

“The question is, what proportion of species will show this response — is it 10 of the fish species? Is it 50 per cent or 80 per cent?” he said.

But there is hope for the future of barramundi and other fish species.

“If you have an experiment where you’ve raised larvae in elevated CO2 and you put them back into normal water, after a few days they start behaving normally again,” Professor Nagelkerken said.

“So there is a chance at reversal, but we need to reduce our CO2 emissions.”

The study has been published in the Nature journal, Scientific Reports.

Source:: ABC News Australia

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