A warmer Antarctica makes a hospitable home for these crabs, endangering an entire ecosystem that has no defenses against them. A crab, Paralomis birsteini, lies on the seafloor some 1,200 meters (3,937 feet) below the surface. Warming waters along the Antarctic peninsula have opened the door to shell-crushing king crabs that threaten a unique ecosystem on the seafloor. Courtesy Richard B. Aronson, Florida Tech

By Eric Niiler
Tue Feb 8, 2011 07:00 AM ET McMURDO STATION, Antarctica — Warming waters along the Antarctic peninsula have opened the door to shell-crushing king crabs that threaten a unique ecosystem on the seafloor, according to new research by a U.S.-Sweden team of marine researchers. On a two-month voyage of the Swedish icebreaker Oden and U.S. research vessel Nathaniel B. Palmer, marine biologists collected digital images of hundreds of crabs moving closer to the shallow coastal waters that have been protected from predators with pincers for more than 40 million years. They are the same kind of deep-water crabs with big red claws that you might find at the seafood counter. “Along the western Antarctica peninsula we have found large populations over like 30 miles of transects. It was quite impressive,” said Sven Thatje, an evolutionary biologist at the University of Southampton in England and chief scientist on the cruise. Finding crabs on the bottom of the ocean isn’t that big a deal. But here in Antarctica, crabs haven’t lived in coastal waters for the past 40 million years. Until now, it’s been too cold. Bottom-dwelling creatures like mussels, brittle stars and sea urchins have not developed any defenses. They have thinner shells, for example. For the same reason, filter feeders, like clams and worms, burrow underground in most regions. The lack of predators has led to a thick canopy of sorts, much like a submarine jungle comprised of flowery feather stars, tube worms and squirming sea spiders. During an interview on board the Oden just after it docked at the main U.S. base in Antarctica, Thatje described how the crabs are moving closer to an ecosystem with no defenses. “The Antarctic shelf communities are quite unique,” Thatje said. “This is the result of tens of millions of years of evolution in isolation.” To explore this underwater world, Thatje and his team of U.S. and Swedish scientists towed an autonomous underwater vehicle (AUV) that scanned the seafloor with a digital camera. Along the way, they encountered thick packs of ice, rough seas and lots of feeding whales. Even though Thatje predicted the crab invasion several years ago in a research paper, he was surprised at seeing so many so quickly. “The pace of changes that we are observing here in the Antarctic, which is the remotest continent on this planet, is quite frightening,” he said. What’s happened is that the waters around the Antarctic peninsula have begun to get warmer. The air temperature has jumped 6 degrees Celsius (10.8 degrees Fahrenheit) since the 1950s, while the average ocean temperature has increased by 1 degree Celsius (1.8 degrees Fahrenheit) over the same time. That change in water temperature has lowered a physiological barrier that has kept the crabs in check. …

King Crabs Invade Antarctic Water