Increasing temperatures and carbon dioxide levels in the world’s oceans may actually speed the growth of starfish, according to research published this week in the Proceedings of the National Academy of Sciences. The results contrast with previous findings of global warming’s negative effects on the five-armed fish’s relatives.

“Mollusks, bivalves, clams and mussels respond negatively to increased carbon dioxide,” says Rebecca Gooding, a doctoral student in zoology at the University of British Columbia and lead author of the paper. On the other hand, she says, compared to their invertebrate cousins, “starfish are growing faster, getting bigger faster, and they’re eating more.”

The starfish’s saving grace, according to Gooding, is that it wears less armor than most other marine invertebrates. (One exception is soft-bodied animals like the sea anemone.) Oceans absorb about half the carbon dioxide humans release into the atmosphere, resulting in more acidic water. Many sea creatures suffer as lowered pH dissolves their calcified shells.

But the effect is not universal. “We need to be careful predicting how species are going to respond to climate change just based on which species they are related to,” says Gooding. “It’s very complex. We actually know very little.”

The researchers put starfish into tanks with carbon dioxide levels and temperatures ranging within current and future levels predicted by the Intergovernmental Panel on Climate Change. In water that contained a relatively high level of carbon dioxide, the sea star, Pisaster ochraceus, grew 67 percent more than its counterparts in tanks set at lower concentrations. An increase of three degrees Celsius (about 5.4 degrees Fahrenheit) boosted relative growth by 110 percent.

Of course, good news for one species doesn’t always apply to an entire underwater ecosystem. Starfish feed on smaller invertebrates, including species not found to do as well under changing ocean conditions.

The mismatch may have a dangerous downside. “This species of sea star just chows down on mussels,” says Gooding. “We expect mussels to grow smaller with rising carbon dioxide since they are stuck in a shell.” The starfish’s dependence on something with shrinking shells makes Gooding wary: “I think mussels are in trouble.”

Photo by Topyti via Flickr