Are King Crabs Invading Antarctic Seas?

A new study suggests not, and points to a paucity of scientific knowledge of life undersea
king crab

The Children’s Museum of Indianapolis

A study published last week challenges the popular academic claim that crabs may have disappeared from Antarctica millions of years ago only to return thanks to warming seas, and one of the authors believes the finding indicates how unprepared scientists are to track the effects of global warming on Antarctic species.

The study, published in the journal PLOS ONE, says previous theories of a recent king crab "invasion" were based on a poor fossil record and an insufficient number of samples. The study argues instead that the crabs never left Antarctica.

"There's nothing unusual about these animals; it's just no one had looked in that part of Antarctica before," said Huw Griffiths, lead author of the study and a marine biogeographer for the British Antarctic Survey.

The theory first emerged in 2005 and was reinforced in 2011 with the discovery of a colony of king crabs in the Palmer Deep, a basin in the continental shelf off the western Antarctic Peninsula. The 2005 study, published in the journal Ecology, said the crabs had gone extinct at least 15 million years ago.

"The west Antarctic Peninsula shelf is warming rapidly and has been hypothesized to be soon invaded by lithodid [crabs]," said a 2011 study published in Proceedings of the Royal Society B.

Deepwater crab fossils are extremely rare, with most decaying deep under ice or destroyed. There are only two king crab fossil records in the world, and none in Antarctica. Griffiths and his team were able to build a more comprehensive sample with the help of modern technology, like underwater vehicles and sensory technology.

"It's very difficult to tell if something's turned up or if it's always been there. You can't see if it's new because it can be living a thousand meters down," Griffiths said. "You could put net down and miss it by a few inches, but it's still always been there."

Scientists unsure how global warming affects Antarctic species
A more worrisome conclusion he has drawn from his findings, however, is how little scientists know about the marine ecosystem of one the fastest-warming areas on the planet.

"If we don't know what's going on with animals as big as king crabs with the current setup and information we have, are we ever going to really be able to stop a true invasion of species when it turns up?" Griffiths asked.

"The only option you really have if you live in cold seas and they're warming up is to go south and go colder, and there's only a certain amount of distance you can keep going south before you hit land," he added.

And the arrival of actual invasive species is looking increasingly likely as ocean temperatures rise. While the rapid melting of the more populated Arctic grabs the most headlines, scientists have been tracking air and ocean temperature in Antarctica since the 1950s. Since then, Griffiths said, they have recorded a 3-degree-Celsius atmospheric temperature rise and a 1-degree ocean temperature rise in the western peninsula, enough to break up sea ice and disrupt plankton blooms, the bedrock of the ecosystem's food chain.

The irony of Griffith's discovery is that, instead of king crabs being the most threatening species in Antarctica, they may be the most threatened.

"Global warming could have already changed these populations, but we don't know because we've only just started to track these changes," he said.

Griffiths acknowledged that, although scientists are now sure the crabs are native to Antarctica, they still don't know what the crabs eat or how they breathe. He added that, of the 17,000 to 20,000 seafloor species in Antarctica, only about 10,000 have names, and about a quarter have only been seen once.

The only way scientists will be able to grasp how climate change is affecting Antarctic marine life, he said, is through a large-scale international effort to collect samples. He said it would take an effort on the scale of the International Polar Year, which involved 16 countries, or the Census of Marine Life, which involved more than 80.

"Given our current understanding," he said, "we won't be able to spot it when climate change is affecting things."


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