‘Faunal exchange’ underway
Some animals are showing up in unusual places, scientists say
In the spring of 2010, a lone grey whale was spotted off the Mediterranean coast of Israel, an event that sparked international interest for an important reason: It was the first North Atlantic sighting of a grey whale, a species restricted to the Pacific Ocean, in about 200 years.
The case is just one example in a recent spate of animals turning up in places they don’t belong — generally, either Pacific species showing up in the Atlantic, or vice versa. Northern gannets, a North Atlantic species, have been spotted off the coast of California several times in recent years, for instance, while several Pacific species of auks, a type of diving bird, have recently been observed in the Atlantic.
It’s a perplexing — yet apparently increasing — trend. And while animals do occasionally wander outside of their ranges, scientists are starting to believe that the recent flurry of movements between the Atlantic and Pacific Ocean basins are early evidence of yet another consequence of climate change.
They’re arguing that as sea ice continues to melt in the Arctic, passageways are opening for certain animals — previously restricted by the ice — to start moving through, enabling them to cross into new territories.
This is the focus of a new paper, released Monday in the journal Global Change Biology, that explores the recent uptick in what the authors refer to as “faunal exchange,” or the movement of wildlife between the Atlantic and Pacific Ocean basins, via the Arctic. Such movements are likely to be made possible by the opening up of passageways, including the famed Northwest Passage, a shipping route through the Arctic currently largely blocked by sea ice.
Marine mammals, such as whales or seals, are often physically prevented from moving through the Arctic by sea ice, which gets in the way of their swimming or prohibits them from coming up to breathe.
And seafaring birds, while capable of flying over the frozen ocean, frequently choose not to do so because the ice prevents them from diving for fish.
But as passageways open up in the melting ice, these animals become more free to move about as they please. Such exchanges could cause a variety of ecosystem-level changes down the road, the authors of the new paper argue, such as the potential for dramatic changes to food webs.
The paper bases its argument on the growing list of recent examples — the grey whales, the gannets and the auks, as well as unusual sightings of other birds and mammals, such as bowhead whales and shearwaters.
“Animals on occasion get lost and they show up in strange places — ‘birds have wings’ is the saying,” said the paper’s lead author, the aptly named Seabird McKeon, a research scientist with the Smithsonian Institution’s National Museum of Natural History.
“There are some species that are more prone to vagrancy than others, and so we do have this backdrop of motion.”
However, “when we’re talking about this exchange, and when the exchange starts becoming noticeable,” that’s when it becomes apparent that a pattern — likely caused by some other, external factor — is emerging.
“Some people might feel that this paper is not loaded down with evidence — they’re basically talking about 10 or 20 species that have been seen out of their geographic range — but they make a good point,” said Larry Crowder, science director for Stanford University’s Center for Ocean Solutions, who was not involved with the paper.
“If there hasn’t been a grey whale in the Atlantic in 200 years and now there is one, that’s a change,” he said, adding, “They certainly didn’t overreach.”
In fact, Kristin Laidre, a principal scientist at the University of Washington’s Polar Science Center (who was also not involved with the paper), said that the ideas in the paper have been floating around the scientific community for some time.
“I think in the kind of ecological studies that consider the consequences of ice loss, the idea that species in the Pacific may become more connected with species in the Atlantic (or vice versa) isn’t really a new idea,” she said.
Laidre was the lead author on a recent paper in Conservation Biology that explored the conservation status of Arctic marine mammals in light of the increasing effects of climate change in the region. The paper touches on the potential for increased movement of animals in the Arctic — and many of the species discussed in that paper also appear in McKeon’s new paper, where he and his colleagues have compiled a list of marine mammals and birds that they expect will move increasingly between the Atlantic and Pacific Ocean basins in the future.
The list includes bird species such as Arctic terns, common eiders, Atlantic puffins and short-tailed shearwaters and mammals such as beluga whales, ringed seals and Atlantic white-sided dolphins.
Altogether, the list contains dozens of species, including both polar species, which typically inhabit open waters above the Arctic Circle, and ice-edge species, which live south of the Arctic sea ice.
While no one can say for sure yet what consequences these types of movements could have, McKeon and his colleagues discuss a number of possible outcomes in the paper. It’s important to note that these outcomes are all speculative for now.
However, scientists can look at past examples of other faunal exchanges to get a sense of what could happen in the future.
One example the authors point to is the Great American Biotic Interchange, which occurred several million years ago when the isthmus of Panama formed, allowing land animals a bridge to cross between North and South America. As the authors note, the fossil record indicates that in this case, mammals from North America invaded South America and outcompeted many of the native species there for resources.
This type of outcome is a potential concern with species crossing from the Pacific to the Atlantic, and vice versa.
Additionally, introducing new predators into an area where they didn’t previously exist can “change food web dynamics profoundly,” Laidre pointed out, noting that the killer whale is a recent prime example. As the authors wrote, killer whales recently “expanded into ice-free areas of Hudson Bay where they were documented preying upon Arctic marine mammals including beluga (Delphinapterus leucas), narwhal (Monodon Monoceros), bowhead, and at least four species of seal.”
There could be genetic changes within migrating populations, as well, as they move and mix with one another. One consequence could be an increase in hybridization, whereby some species or subspecies could eventually be genetically phased out of existence, suggested Ryan Terrill, a Ph.D. candidate at Louisiana State University’s Museum of Natural Sciences, who served as a peer reviewer on the paper.
On the other hand, this type of mixing could add genetic diversity to small subpopulations, which could be a good thing, said Laidre. In general, Laidre said, the effects of the exchange will not necessarily be all negative.
McKeon noted, “Populations of animals have been moving as long as there have been populations of animals.” So it’s not necessarily a good idea to try and stop them. The key, he said, is rather to increase the monitoring of wildlife as they move about in the Arctic to better understand which species are ending up where and how they might be affecting their environment.
“If there hasn’ t been a grey whale in the Atlantic in 200 years and now there is one, that’ s a change.
LARRY CROWDER SCIENCE DIRECTOR FOR STANFORD UNIVERSITY’S CENTER FOR OCEAN SOLUTIONS