Ocean Acidification Changing Fishes' Sense of Smell, Predators' Scent Becomes Irresistible

clownfish photo

Photo via National Marine Sanctuaries via Flickr CC

As the ocean absorbs more of the carbon dioxide we're pumping into the atmosphere, its chemistry changes and it is becoming much more acidic. This ocean acidification is causing problems from bleaching coral reefs to altering the make-up crustacean's shells. But for the first time, scientists are finding that it is also playing havoc with fishes' sense of smell. More acidic oceans is making it harder for fish to smell when predators are nearby, making them more likely to end up as prey. According to the Telegraph, marine biologists have found that fish growing up in water with high levels of CO2 are not only unable to smell predators, but are sometimes even attracted to their scent. The younger fish tend to take greater risks like swimming farther from shelter, and biologists worry that fish populations could further decline as oceans become more acidic.

To test their findings, researchers looked specifically at clown fish and damselfish larvae in a lab. After just a few days living in water with heightened CO2 levels, the fish had marked changes in their ability to smell and when given the choice of two flow chambers -- one with and one without the scent of predators -- the fish larvae spent 93% of their time in the flow with the predator's scent. Fish that were not exposed to acidic water avoided the flow that carried the scent of predators.

What's worse, when the fish were released, those that were raised in the acidic water had mortality rates between five and nine times higher than fish raised in normal water. Though the exact reason why the heightened CO2 changes a fish's ability to detect predators or causes them to be attracted to their smell, the riskier behavior exhibited could mean various fish species will struggle to survive as oceans acidify.

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