This king crab was spotted in 1100 meters of water, shallower than has ever been spotted off the Antarctic coast.

Polar Science From the Deep--Part II

John is a Science contributing correspondent.

Changes are afoot beneath the icy waters around Antarctica--on eight feet, to be exact. With the help of waters warmed by climate change, the king crab, which has not set claw in the shallow Antarctic waters in 15 million years, may be returning.

Since their last report from the U.K. research vessel James Clark Ross off the coast of Antarctica, the team of 22 scientists has been working in 4-hour shifts around the clock to study the rocky slope that connects the continental shelf with the deep seafloor. The only crew member who never sleeps is Isis, the ship's remotely controlled robot, which has been prowling the rocky surface in search of king crabs.

A host of shell-cracking monsters such as the king crab used to thrive in the shallow waters around Antarctica. But about 15 million years ago, a shift in the southernmost tectonic plates gave birth to today's frigid Antarctic circumpolar current. The waters have remained close to 0°C ever since. The predators' physiology cannot cope with the cold, and they disappeared to the deep sea (below 1500 meters), where lower currents keep the temperature closer to 2°C. Their absence from shallower waters has allowed a unique community of Antarctic filter feeders to flourish for millions of years. More recently, global warming has been cranking those waters above 1°C, a temperature fit for a king crab.

While Isis was scanning the continental slope at a depth of 1100 meters late at night on 25 January, a pair of beady eyes stared back in the video screen onboard the Ross. A king crab 50 centimeters in diameter was picking its way across the rocks, closer to Antarctica's shallow waters than has ever been spotted before. From the ship, Dave Turner, a technician from the U.K. National Oceanography Centre of the University of Southampton (NOCS) who pilots Isis from the Ross, used a remote-controlled robotic arm to pluck the crab and pop it into a sampling box. The crab's DNA will be sampled and sequenced back on land. By comparing mutation markers in the DNA, the researchers will be able to test whether the crab comes from known populations, for example near the coast of Chile to the north. "If this is the start of an invasion, it could spell the end for the biological uniqueness of shallow-water communities along the Antarctic Peninsula," writes Sven Thatje, a marine ecologist at NOCS, from the ship.

Stay tuned for another report of science in action from the Ross, which finishes her cruise along the coast of Antarctica 6 February.

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