According to latest significant findings of a breakthrough research in Australia, baby fish may become easy meat targets for predators as the world's oceans become increasingly acidic due to rising carbon dioxide emissions from human activity.
The behavior of baby fish changes drastically in ways that cut down their survival chances by 50 to 80 per cent, scientists have found based on a series of experiments published in the recent issue of the Proceedings of the National Academy of Science (PNAS).
Professor Philip Munday from the Australian Research Council's Centre of Excellence for Coral Reef Studies (CoECRS) at James Cook University said as carbon dioxide increases in the oceans, the water becomes slightly more acidic.
The acidification of the ocean reaches to a point that it substantially changes the sense of smell and behavior of larval fish.
He said, Instead of avoiding predators, they become attracted to them. They appear to lose their natural caution and start taking big risks, such as swimming out in the open - with lethal consequences.
The change in fish behavior could have serious consequences on the sustainability of fish populations as fewer baby fish will survive to replenish adult populations, said Dr Mark Meekan from the Australian Institute of Marine Science, who is also co-author of the paper.
Dr Meekan said, Every time we start a car to turn on the light part of the resulting carbon dioxide is absorbed by the oceans, turning them slightly more acidic.
The ocean pH could fall further if humans continue emitting carbon dioxide at the current increasing rate.
Dr Meekan said the adverse effects on corals, shellfish, plankton and other organisms with calcified skeletons have already been observed, and now we are starting to see the effects on other marine life, such as fish.
The previous research by Prof Munday and colleagues discovered that baby Nemo clownfish were unable to find their way back to their home reef under increasing acidic conditions.
The recent experiments involve a broader range of fish species and show that acidified sea water causes a fish to adopt a dangerous behaviour change.
In the experiments, they exposed baby fish to the created sea water that we will have in the latter part of this century -if we keep burning coal and coil at current rates, which will result in atmospheric carbon dioxide levels of 750-1,000 parts per million - and returned them to the sea to observe their behavior.
Upon their release on the reef, it was noted that they swam further away from shelter and their mortality rates were five to eight times higher than those of normal baby fish, said Prof Munday.
The study findings demonstrate that additional carbon dioxide absorbed into the ocean will reduce recruitment success and have far-reaching consequences for the sustainability of fish populations, concluded the team of scientists.