London: Carbon dioxide in the ocean acts like alcohol on fish and leaves them less able to judge risks, making them prone to losing their senses, a new study has claimed.
The intoxication caused by carbon dioxide adds to the threats posed by global warming and ocean acidification to marine ecosystems.
Almost 2.3 billion tonnes of CO2 caused by human emissions dissolves into the world’s oceans every year, turning it all the more acidic.
Philip Munday and his colleagues from James Cook University in Townsville, Queensland, Australia, had previously found that if a reef fish is put in water with more CO2 levels in it than what is normal, they become bolder and more attracted to odours they would normally avoid, including those of predators and unfavourable habitats.
Munday and his colleague Goran Nilsson at the University of Oslo, Norway, have now discovered that carbon dioxide leads to riskier behaviour by interfering with a neurotransmitter receptor called GABA-A.
They nurtured clownfish larvae in seawater with normal and elevated CO2 levels. When the Amphiprion percula reached adulthood, they were given a choice between a water stream containing the odour of common predators like the rock cod or a stream lacking predatory odours.
Those reared in high levels of CO2 swam towards rock cod’s scent almost 90 percent of the time, whereas those that had enjoyed normal levels of CO2 avoided the predator’s scent most of the time.
On treating the clownfish bred under CO2-rich conditions with gabazine, a chemical that blocks the GABA-A receptor helped them regain their senses.
Fish treated this way swam towards the predatory smell only 12 percent of the time.
“The fact that we could use a specific blocker for the GABA-A receptors to reverse the behavioural alterations proves that this receptor is involved in the CO2 effects,” New Scientist quoted Nilsson as saying.