Rising levels of CO2 dissolved in oceans are compromising the survival skills of fish, according to Australian researchers. By the end of the century, the levels predicted for the oceans will interfere with fish’s ability to hear, smell, turn and evade predators, claimed Professor Phillip Munday of the ARC Centre of Excellence for Coral Reef Studies and James Cook University.
“For several years our team has been testing the performance of baby coral fish in sea water containing higher levels of dissolved CO2 – and it is now pretty clear that they sustain significant disruption to their central nervous system, which is likely to impair their chances of survival,” he explained, TG Daily reports.
The reason is that high CO2 levels in the sea disrupt a vital brain receptor in fish and alter their behaviour and sensory ability.
“We’ve found that elevated CO2 in the oceans can directly interfere with fish neurotransmitter functions, which poses a direct and previously unknown threat to sea life”, he says.
The researchers examined how baby clown and damsel fish fared alongside their predators in CO2-enriched water and found that the baby fish suffered much higher rates of attrition than the predators. The baby fish had a harder time locating a reef to settle on and detecting the warning smell of a predator fish.
The frightening scent of predators could suddenly become alluring to fish, neurobiologist Andrew Dittman of the National Oceanic and Atmospheric Administration’s (NOAA) Northwest Fisheries Science Centre in Seattle, US pointed out, Science News reports.
“But we suspected there was much more to it than the loss of ability to smell”, said Munday.
It was also determined that the fishes’ sense of hearing was impaired — so they no longer avoided reef sounds during the day and became much more vulnerable to predators.
The fish lost their natural instinct to turn left or right – an important factor in schooling behaviour, which is important because lone fish are easily eaten by predators.
“All this led us to suspect it wasn’t simply damage to their individual senses that was going on – but rather, that higher levels of carbon dioxide were affecting their whole central nervous system”, Munday told.
It appears that high CO2 directly and harmfully stimulates a receptor in the fish brain called GABA-A. The main impact is likely to be felt by some crustaceans and by fish, especially those which use a lot of oxygen.
“We’ve now established it isn’t simply the acidification of the oceans that is causing disruption – as is the case with shellfish and plankton with chalky skeletons – but the actual dissolved CO2 itself is damaging the fishes’ nervous systems”, he concluded.
Around 2.3 billion tonnes of human CO2 emissions dissolve into the world’s oceans annually, spawning changes in the chemical environment of fish and other species, Munday added. (Source: FIS.COM)