By Katherine Nightingale for ABC Science Online
Global warming could have an unexpected effect on the clownfish star of Finding Nemo and his kind, by making them indulge in risky behaviour, say researchers.
Previous research indicates that as carbon dioxide (CO2) levels in the atmosphere climb the surface water of the oceans could become more acidic.
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.
They publish their research this week in the Proceedings of the National Academy of Sciences journal.
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," Mr Munday said.
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.
The researchers are now trying to pin down why acidification causes the fish to behave more boldly, as well as looking at the wider effects on population balance in reef ecosystems.
Mr Munday says, for example, different species could have different tolerances, and acidification could make predators more or less inclined to eat.
Professor Geoffrey Jones, also of JCU and the ARC Centre of Excellence for Coral Reef Studies, said the research took 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," Mr Jones said.
"However, given that the rate of CO2 increase is unprecedented, there are no grounds for optimism."