Fish from acidic oceans cannot detect predators

A new study has discovered that fish from acidic ocean waters were less able to smell – and thus detect – predators than fish from normal coral reefs. The study confirms laboratory experiments that the behaviour of reef fish is seriously affected by increased carbon dioxide concentrations in the ocean.

“These results verify our laboratory findings,” said Danielle Dixson at the Georgia Institute of Technology in Atlanta. “There’s no difference between the fish treated with CO2 in the lab in tests for chemical senses versus the fish we caught and tested from the CO2 reef.” The research was published in mid-April in the scientific journal Nature Climate Change.

The pH of normal ocean surface water is around 8.14. The new study examined fish from so-called bubble reefs at a natural CO2 seep in Papua New Guinea, where the pH is 7.8 on average. With today’s greenhouse gas emissions, climate models forecast pH 7.8 for ocean surface waters by 2100, according to the Intergovernmental Panel on Climate Change (IPCC).

Previous research had led to speculation that ocean acidification might not harm fish if they could buffer their tissues in acidified water by changing their bicarbonate levels. But this latest research shows that fishes’ sensory systems are impaired by ocean acidification conditions. “They can smell but they can’t distinguish between chemical cues,” Dixson said.

Fish can smell a fish that eats another fish and will avoid water containing the scent. In Dixson’s laboratory experiments, control fish given the choice between swimming in normal water or water spiked with the smell of a predator will choose the normal water. But fish raised in water acidified with carbon dioxide will choose to spend time in the predator-scented water.

Juvenile fish living at the carbon dioxide seep and brought onto a boat for behaviour testing had nearly the identical predator sensing impairment as juvenile fish reared at similar CO2 levels in the lab, the new study found.

In future work, the research team will test if fish could adapt or acclimate to acidic waters. “Whether or not this sensory effect is happening generationally is something that we don’t know,” Dixson said.


Picture credit: Richard Ling/Creative Commons

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