Invasion of the Body Smashers

Right now, an army of exoskeleton-crushing king crabs is marching out of the depths of Antarctica’s Marguerite Bay, heading closer to shore—territory they haven’t crawled over for tens of millions of years. Until the last few decades, a curtain of near-freezing water pouring off the continent has kept the creatures from entering shallower waters, where a rich array of filter-feeding brittlestars, sea lilies, feather stars, sponges, anemones, and other invertebrates thrive on the seafloor. But now that cold-water barrier is warming, allowing the crabs to return from exile. And they arrive hungry.

As the decapods climb higher and higher up the continental shelf, scientists fear the predators will mow down vast populations of defenseless invertebrates, ripping apart the food web and devastating biodiversity one tasty morsel at a time.

On a typical coastline, you’ll see filter-feeders burying themselves in the sand to escape detection from predators. But here on the southernmost continental shelf, mollusks and other invertebrates have had little to fear for many, many millennia. The crab-free conditions have created a unique ecosystem—a sort of window into what marine communities looked like before durophagous (shell-crushing) predators started evolving 200 million years ago.

Compared to the slow-moving, frankly sort-of wimpy predators that have historically inhabited the continental shelf—starfish, ribbon worms, and the like—king crabs are chitin-plated MechWarriors. They’re big, quick, and equipped with claws that can crunch through exoskeletons like the shiny, silver crackers they give you at seafood restaurants.

The average brittlestar or sea lily is no match for these marauders who are, unfortunately, not just pillaging and passing through. In a paper published this week in the Proceedings of the National Academy of Sciences, researchers have found ample evidence that they may be here to stay.

Of nearly 500 king crabs caught in traps in Marguerite Bay and many more captured by underwater camera vehicle surveys, the scientists observed Paralomis birsteini successfully molting, several locked in “precopulatory embrace” (read: crab foreplay), and one carrying eggs so far advanced that they had fully formed eyes.

As to why the crabs have been suddenly released from Davey Jones’ locker, lead author Richard Aronson, a marine ecologist from the Florida Institute of Technology, doesn’t mince words. “This is one of many examples of the unintended consequences of climate change,” he says. “The world is changing rapidly.” According to a study published last year, the temperatures of the seabeds around Antarctica have risen by nearly 1.5 degrees Celsius over the past 50 years—approximately twice the globally averaged rate of warming.

If the king crabs and other shell-crackers are successful in their expansion, the seafloor around the Antarctic will start to look like one found everywhere else on earth. Aronson likens this trashing of our natural inheritance to throwing Michelangelo’s David in the dumpster.

But that may not be all that’s at stake. One of the coauthors of this study, James McClintock, a biologist at the University of Alabama, is testing the tissues of some animals found on the shelf for compounds that might one day help in the fight against diseases like melanoma. So with humans potentially affected by the crab invasion as well, there seem to be plenty of reasons to care about what’s crawling around at the bottom of the sea at the bottom of the world.