Rising levels of dissolved carbon dioxide in the world’s oceans could drive fish “crazy,” seriously threatening their survival, according to Australia’s ARC Centre of Excellence for Coral Reef Studies.

Earth’s oceans are currently the largest natural “sink” for carbon dioxide emitted into the atmosphere, and the amount of CO2 they absorb is rising along with atmospheric levels of the greenhouse gas. The more carbon dioxide seawater absorbs, the more acidic it also becomes.

That increased acidity poses a threat to shellfish, because more acidic water can dissolve the calcium carbonate that makes up their shells. But now it looks as if dissolved carbon dioxide itself is also bad for sealife, by affecting their brains and central nervous systems.

In fact, the carbon dioxide levels predicted for the oceans by the end of this century could make fish “crazy,” affecting how they hear, smell, turn and avoid danger, researchers at the Arc Centre say. Young fish appear to be particularly vulnerable, losing a significant amount of their ability to hear predators or to move left and right in a school.

“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,” said Philip Munday, who is also a professor at James Cook University.

While the research team studied the impacts of CO2 on clown fish and damsel fish, their study indicates that other fish with high oxygen consumption levels — including some important to the fishing industry — could be similarly affected.

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