Sure, the planet’s increasing carbon dioxide levels are making the oceans more acidic, but what does that really mean for sea life? We’ve already heard that the ocean’s changing chemistry is damaging corals and interfering with mussels, but that’s just the beginning. It turns out things could get seriously weird.

In a paper published this week in The Proceedings of the National Academy of Sciences, researchers led by Philip L. Munday of James Cook University have given us a concrete example: the increased CO2-levels make some fish purposely swim towards predators.

As part of his experiment, Munday used a Y-shaped maze to force baby clownfish to choose between two paths. One path reeked of rock cod, a natural predator; the other had no danger scents. Munday’s team compared the choices of fish raised in water of varying carbon dioxide concentrations, from today’s levels of 390 parts per million up to future expected levels of 850 ppm.

Those clownfish raised in today’s CO2 concentrations behaved as you might expect: ninety percent of the time, they avoided the rock cod stink and, after little more than a week of training, they always chose the safe path. But at 700 ppm, something alarming happened. The fish headed straight for the predator’s smell 74 to 88 percent of the time. At 850 ppm, after about eight days, every single fish chose the path to death.

The scientists speculate that the acidic waters damage the fishes’ sense of smell, which along with avoiding predators, they must use to find family and home:

“They can’t distinguish between their own parents and other fish, and they become attracted to substances they previously avoided. It means the larvae will have less opportunity to find the right habitat, which could be devastating for their populations,” said Kjell Døving, a co-author from the University of Oslo. [Guardian]

For all the details, check out Ed Yong’s post in Not Exactly Rocket Science.

Related content:
80beats: No More Speculation: Scientists Prove Ocean Acidification is Already Underway
80beats: Ocean Acidification: Worse Than the Big Problem We Thought It Was
80beats: Ocean Acidification Could Leave Clown Fish (Like Nemo) Lost at Sea
80beats: A Glimpse Into a Future With Acidic Oceans
80beats: In a More Acidic Ocean, Coral Reef “Skeletons” May Crumble

Image: flickr / Sean McGrath