When ocean temperatures start to rise, fish hightail it to cooler water
Photo credit: Simon Thorrold, Woods Hole Oceanographic Institution
Scientists have new evidence that as ocean temperatures continue to rise, coral-reef fish will probably opt instead to relocate to cooler water.
In a study using a fish found in coral reefs around the world, the blue-green damselfish, Chromis viridis, researchers found that the fish were capable of adapting to living in water 2-4 degrees Celsius above their normal summer temperatures; however, when given the slightest chance, the fish moved to cooler water.
“When fish have to adapt to increased temperature, there are physical consequences. They may not be able to handles stress, or reproduce, or even grow,” said marine scientist Dr. Jacob Johansen from The University of Texas at Austin. “But, when they seek out temperatures that they’ve evolved to be in over thousands of years, they can mitigate the impact of increasing temperatures and not sacrifice critical physiological processes.”
Johansen and fisheries biologists from the University of Copenhagen and James Cook University collaborated on the study, published in the journal Global Change Biology. The blue-green damselfish, Chromis viridis. Credit: Jodie Rummer
Historically fish have adapted to changes in temperature over a long evolutionary timescale, roughly one degree Celsius temperature increase per million years. Current predictions for rising temperature are much greater, with sea surface temperature predicted to increase by 2-4 degrees Celsius by the end of the 21st century.
Instead of looking into how fish can adapt, the new research took a different approach by asking, what if fish moved? In fact, what if entire ecosystems were capable of moving to the cooler temperatures, towards the poles or in deeper water?
There is already evidence that many coral reef fish and pelagic fish, like tuna, have moved in response to warmer ocean waters. The researchers found evidence that this also might occur with blue-green damselfish, and they stressed the need to investigate more fish species, including commercial fish species that economies rely upon.
“This study shows, that there is a mechanistic explanation for why fish may move, faced with a choice, and now we have a way of testing it,” Johansen said.
