As the world has warmed over the past few decades, scientists have recorded fish, butterfly, and bumblebee species moving to new home ranges, seemingly in search of cooler temperatures. Yet it's still difficult for scientists to predict exactly which species will move in response to global warming, and how far they'll go. After all, it's not as if a whole ecosystem moves north or south at once; some members go and some stay, creating new dynamics between the migrants and the animals they meet when they arrive at their new destination. Now, however, a new study offers a step toward such future-telling, at least for sea animals.
In a study published this week in the journal Ecology Letters, a team of scientists from Canada, Australia, and the United Kingdom identified which traits are common to certain sea animal species that have extended their ranges further poleward, into cooler waters. It's a step toward predicting which other animals will move in response to climate change. If such predictions improve in the future, governments and other groups might better prepare for a myriad of changes, including a sudden emergence of commercially catchable fish in a nation's waters. Such changes can throw industries into "chaos," says Jennifer Sunday, the study's lead author and a research fellow in zoology at the University of British Columbia. "Instead of having a Wild, Wild West, why don't we monitor this change and think about how to help fishers transition from one resource to another?"
Species that originally lived in a large, north-to-south span along the shore were more likely to push the envelope of where they lived even further.
Sunday and her colleagues analyzed data about the home ranges of 104 fish and invertebrate species living off the coast of southeastern Australia. Using data over several points in time, they were able to see whose home ranges have changed, and by how much. From those data, the scientists gleaned which traits are common to those sea animals extending their ranges the most.
Species that originally lived in a large, north-to-south span along the shore were more likely to push the envelope of where they lived even further, the authors found. The researchers think that's because species with big ranges are likely to be generalists who are better equipped to deal with new habitats. Being able to swim—and not just crawl, or worse, not locomote at all—helps. So does being omnivorous, versus being a carnivore or an herbivore.
These traits are just a starting point. Scientists still need to answer some big questions before they'll be able to predict exactly which animals will come and go from a region when it warms. They'll have to check whether the traits that make sea animals mobile in southeastern Australia also apply elsewhere in the world. Furthermore, there's continuing debate about which traits really matter—a previous study had found that characteristics such as, say, what fish ate didn't explain their movement as much as simple water temperatures did.
Meanwhile, southeast of Australia, climate change is already affecting lobster fishers. The warming waters have lured sea urchins to the ocean floor around Tasmania, where they've eaten so much kelp, there's not enough left to support the region's large rock lobster population. Because of the unique dynamics of the water currents there, the sea southeast of Australia has actually warmed three to four times faster than average. "Because it's happening so much faster here, this is a window into what might be happening everywhere, a little bit more down the line," Sunday says.