The Next Threat to Antarctica Is Coming From the Deep

King crabs are starting to creep onto the continental shelf in Antarctica, which could create a dire situation for the creatures living there.

King crab. (Photo: National Oceanic and Atmospheric Administration/Flickr)

Sep 28, 2015· 2 MIN READ
Katharine Gammon has written for Nature, Wired, Discover, and Popular Science. A new mom, she lives in Santa Monica.

Antarctica’s shallow continental shelf is home to brightly colored brittle stars, purple urchins, and many other weird and wonderful creatures. Now, for the first time in around 30 million years, the fragile ecosystem may also be home to some destructive predators: king crabs.

They’re rising from the region’s deeper waters, and it’s thanks to climate change.

Because of the ice, the shelf’s shallow waters have typically been a few degrees colder than deep waters off Antarctica, which has kept the crabs from invading. But over the past 50 years, Antarctica’s water temperatures have increased 1.5 degrees Celsius—more than twice the global average—leaving space for king crabs to move up the water column.

The problem with that, said Florida Institute of Technology biologist Richard Aronson, is that the sea stars, urchins, and snails living on Antarctica’s shelf don’t have the specialized defenses to ward off the shell-crushing predators.

RELATED: Antarctica’s Ice Shelves Are Vanishing, and That Could Mean Higher Sea-Level Rise

“Predators have been absent from these communities for a long time—possibly tens of millions of years—and those communities have evolved to be rather different than a clam bed in Cape Cod,” Aronson said. “If the crabs move, they could knock down these populations of their prey that have been sitting around in their splendid protection for a long time.”

The findings come in a study, published Monday in the journal Proceedings of the National Academy of Sciences, for which Aronson and his colleagues towed a camera rig behind an underwater vehicle to observe king crabs on the continental slope. At depths between 2,800 and 7,500 feet, they found an average of 4.5 crabs per 10,000 square feet—enough to be considered a large population.

The team also found female crabs that were filled with eggs, which shows it’s not just a few explorers but a sustainable population, Aronson said. When the researchers probed the bellies of the crabs, they found they were eating the mollusks and sea stars endemic to the continental shelf.

“The outer parts of the shelf, between 450 and 550 meters [1,400 to 1,800 feet] of depth, are already OK for crabs to survive,” said Aronson. “Where the crabs are, we see fewer fragile creatures. So it’s hard not to say that the crabs are eating this stuff.”

It’s difficult to say how fast the crabs are moving, though until 2003, scientists had never recorded any king crabs on the continental shelf. For now, Aronson said, Antarctica’s top layer of water remains too cold for the crabs to survive.

So what other threats do crabs bring to the Antarctic seafloor? Aronson said the unique environment could hold a treasure trove of discoveries, if we can get to them before the crabs do.

Scientists are looking into bioprospecting—finding useful compounds to treat human diseases. One anti-melanoma compound found in polar sea squirts may hold the potential to save human lives.

There’s also an ethical and aesthetic argument for saving the environment.

“What kind of world do you want to live in?” Aronson asked. “Do you want a less exuberant world or one that is lively and full of differences?”

The key to holding back the onslaught of crabs rests in keeping the Antarctic’s ocean temperatures from rising—and the key to avoiding a warming ocean is reducing greenhouse gas emissions. “We need to modify our lifestyles in a reasonable way to control emissions, or we are going to be in a lot of trouble,” said Aronson. “Climate change is going to continue to be full of surprises, and most of them are nasty surprises.”