Fish from acidic ocean less able to smell predators

Researchers have said that fish living on coral reefs where carbon dioxide seeps from the ocean floor are less able to detect predator odor than fish from normal coral reefs.

Danielle Dixson, an assistant professor in the School of Biology at the Georgia Institute of Technology in Atlanta, said there's no difference between the fish treated with CO2 in the lab in tests for chemical senses versus the fish they caught and tested from the CO2 reef.

Philip Munday, from James Cook University in Australia, was the study's lead author.

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.

Carbon dioxide released into the atmosphere is absorbed into ocean waters, where it dissolves and lowers the pH of the water. Acidic waters affect fish behavior by disrupting a specific receptor in the nervous system, called GABAA, which is present in most marine organisms with a nervous system. When GABAA stops working, neurons stop firing properly.

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.

The research has been published online of the journal Nature Climate Change.