Ocean Acidification Makes Oceans Smell Funny

As rising levels of atmospheric carbon dioxide create more acidic oceans, their waters may start to smell funny and that change could prove possibly fatal to fish.

New research has found that the larvae of two kinds of coral reef fish -- clownfish and damselfish -- lose the ability to distinguish the smell of predators from non-predators and fail to avoid the smell of predatory fish when raised in waters at acid levels predicted for the end of this century.

As a consequence, these bold-acting, acid-exposed fish suffered five to nine times more deaths in the bellies of predators than their counterparts raised at today's acid levels, the researchers reported today at a meeting of the Ecological Society of America in Pittsburgh, Penn.

A disrupted sense of smell as the ocean acidifies may affect fish of many types, researchers believe, though more study is needed.

"Chemical signals are probably dominating the lives of most animals in the water. If they can no longer discriminate between chemical signals, that's bad news," said Jelle Atema of Boston University, who was not a part of the study, but who hopes now to explore the effect in sharks.

"What we don't know is how it will play out over a much longer time scale," Atema added. "If these effects persist, it would create total havoc with the natural interactions between fish and presumably also with crustaceans, including their ability to find food and homes and everything."

The fish may have time to adapt, depending on how fast ocean acidification happens, said Danielle Dixson of James Cook University in Townsville, Australia, who led the study.

"There does appear to be some room for natural selection to select for the tolerant larvae," she said. Dixson found that at intermediate acid levels, a proportion of larvae could still distinguish and avoid the smell of predators.

Exactly how acidic waters create this disorienting effect is not yet certain.

"It's not an inability to smell, it's more like an inability to process the smell correctly," Dixson said.

When presented with water carrying a predator's smell and water with no smells of other fish, the acid-reared larvae were attracted to the predator's smell.

When offered either predator-smelling water or water with the smell of a non-predatory fish, the larvae were equally attracted to both smells. "(Acid)-treated fish larvae were attracted to everything." Dixson said.

"A lot of signals in the body are passed through pH gradients. (Increased acidity) could be affecting the processing of the information," she said. This idea is consistent with her finding that the damage is not permanent -- it's reversed after a few days in normal waters.