Ocean Acidification May Cause Sharks to Avoid Hunting Prey and Impact Sense of Smell

As climate change causes the acidity of ocean waters to increase, more and more species are being affected. Now, scientists have found that increased acidification could actually rob sharks of their ability to sense and smell food.

Carbon dioxide that's released into the atmosphere is absorbed by ocean waters. Over time, enough CO2 can lower the pH of the water and cause it to become more acidic. This can affect animals that create calcium carbonate shells, since the acidic waters partially dissolve the shells. In addition, the acidification can impact fish behavior.

Intrigued by this, scientists decided to see whether acidic waters could impact shark behavior. A total of 24 sharks from local waters around Cape Cod were studied in a 10-meter-long flume. The flume resembled two lands of a swimming pool, and odor from a squid was pumped down one lane of the flume. Normal seawater was pumped down the other lane.

The sharks, predictably, adjusted their position in the flume in order to spend more time on the side containing the squid odor. Yet all that changed when scientists changed the acidity of the waters. Sharks in normal sweater and mid-level carbon dioxide spent more than 60 percent of the time in the water stream with the squid odor. Yet sharks in water that had high levels of carbon dioxide spent less than 15 percent of their time in the water stream that smelled of squid. In fact, these sharks avoided the odor even when it was on the side of the flume that they naturally preferred.

"The sharks' tracking behavior and attacking behavior were significantly reduced," said Danielle Dixson, one of the researchers, in a news release. "Sharks are like swimming noses, so chemical cues are really important for them in terms of finding food."

The findings reveal that high acidity may just impact a shark's ability to hunt. While sharks have adapted to ocean acidification conditions in the past that are projected for the future, they've never had to adapt to changes happening as quickly as they are today.

"It's the rate of change that's happening that's concerning," said Dixon. "Sharks have never had to deal with it this fast."

The findings are published in the journal Global Change Biology.