Global warming could lead small fish to engage in 'risky' behaviour

Melbourne, July 7: A study has suggested that global warming could have an unexpected effect on small fish, like the clownfish, by making them indulge in risky behaviour.

A previous study had shown that as carbon dioxide (CO2) levels in the atmosphere climb, the surface water of the oceans could become more acidic.

And scientists have already shown that this acidification interferes with fish larvae's sense of smell and ability to find a suitable home.

Now research led by marine researcher Professor Philip Munday of James Cook University (JCU) has found it could also make fish less aware of - and even attracted to - predators.

As part of the study, the researchers put clownfish and damselfish larvae into seawater equivalent to that which would be found if the atmosphere contained 700 ppm and 850 ppm of CO2 - levels that could be reached by the end of the century.

They found that after four days, half of the larvae in the 700 ppm group were less able to detect the smell of a predator, while all the larvae in 850 ppm group were actually attracted to the predator scent.

Damselfish larvae that were then released onto a reef were more active and behaved more boldly than normal, spending less time near shelter and more time near predators.

They were also five to nine times more likely to die than 'normal' fish born in 390 ppm conditions.

The results suggest this could have a huge impact on ocean biodiversity.

"Being attracted to the smell of a predator isn't likely to be a very good thing," ABC Science quoted Munday, who is a professorial research fellow at JCU's School of Marine and Tropical Biology and the Australian Research Council's Centre of Excellence for Coral Reef Studies.

Professor David Booth, a marine ecologist at the University of Technology Sydney who was not involved in the study, says the behavioural choices made by young fish are thought to strongly affect populations.

"This finding of negative effects on such choices could have profound implications for the dynamics of fish populations," he said.

Professor Geoffrey Jones, also of JCU and the ARC Centre of Excellence for Coral Reef Studies, says the research takes the level of concern about the effects of climate change on coral reef fish "to a whole new level".

"Without drastic action to cut emissions, all we can do is hope that fish will be able to adapt," Jones said.

"However, given that the rate of CO2 increase is unprecedented, there are no grounds for optimism," he added.

The research has been published in the Proceedings of the National Academy of Sciences journal.

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