Increased Carbon Dioxide Levels Debilitating Sea Fishes

A new study has found that rising human carbon dioxide emissions may in fact be affecting the brains and central nervous systems of sea fishes, decreasing their inherent ability to survive.

Carbon dioxide concentrations predicted to occur in the ocean by the end of this century will interfere with fishes’ ability to hear, smell, turn and evade predators, says Professor Philip Munday of the ARC Centre of Excellence for Coral Reef Studies and James Cook University in Townsville, Australia.

“For several years our team have been testing the performance of baby coral fishes 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,” Prof. Munday says.

The study, entitled  “Near-future CO2 levels alter fish behaviour by interfering with neurotransmitter function” and published in the journal Nature Climate Change, Professor Munday and colleagues report on their findings which show that high levels of carbon dioxide in sea water disrupts a key brain receptor – GABA-A – leading to a reversal in their behaviour and sensory abilities.

“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,” Prof. Munday says.

The researchers studied how baby clown and damsel fishes performed alongside their predators in water saturated with carbon dioxide. The predators were somewhat affected, but the baby fish suffered much higher rates of attrition.

“Our early work showed that the sense of smell of baby fish was harmed by higher CO2 in the water – meaning they found it harder to locate a reef to settle on or detect the warning smell of a predator fish. But we suspected there was much more to it than the loss of ability to smell.”

The team the looked at whether a fishes’ sense of hearing was affected by the increased carbon dioxide levels. They fond that the fish were confused and no longer avoided reef sounds during the day, making them easy prey for predators.

Their research also showed that the fish tended to lose their natural instinct to turn left or right, an important factor in schooling behaviour which, again, only served to increase their risk of being 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.”

Prof. Munday said that around 2.3 billion tonnes of human CO2 emissions dissolve into the world’s oceans every year, causing changes in the chemical environment of the water in which fish and other species live.

“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.”

Source: ARC Centre of Excellence for Coral Reef Studies

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