King Crabs Are Invading Antarctica, Thanks to Warming Oceans

King crabs are poised to invade the delicate ecosystem on the Antarctic continental shelf. Richard B. Aronson and James B. McClintock

The unique life that adorns the sea floor west of the Antarctic peninsula exists nowhere else. There, scientists have found all sorts of rare invertebrates, like sponges and sea anemones, sea lilies and feather stars, as well as filter-feeders called bryozoans. This last group thrives upon a continental shelf where the water is relatively shallow and cold, cold enough that it has prevented predators from living there for eons. But that may soon change as the water warms.

Richard Aronson, a researcher at Florida Institute of Technology, says that the ecosystem looks like something out of a time-capsule, resembling the sea floor of hundreds of millions of years ago in the Paleozoic era, before crabs and fish evolved. All these creatures live out on the open on the sea floor, because they have basically no predators, Aronson explains. (Elsewhere, in warmer areas, such invertebrates often have to burrow into the mud to avoid predation.)

This may not last forever. A study by Aronson and colleagues has shown that there is a thriving population of king crabs on the eastern continental slope adjacent to the shelf. The paper, published September 28 in the journal Proceedings of the National Academy of Sciences, found that the conditions on the continental shelf appear suitable for the crabs, and that there are no known impediments to the crab's migration.

Specifically, the water now appears to be warm enough for the crabs to live on the shelf, a vast expanse of terrain west of the Antarctic peninsula. Temperatures in the shallow waters there have increased by 2.7 degrees Fahrenheit in the past 50 years, Aronson says. Other conditions there—such as the salinity, abundance of choice food and type of sediment on the sea floor—appear ideal for the crabs to thrive as well.

Aronson's findings are similar to those of Craig Smith, a biological oceanographer at the University of Hawaii at Manoa. His group found another population of king crabs in an area called the Palmer Deep, north of Aronson's study site. These crabs had to have ended up here by crossing over the continental shelf in the recent past, as temperatures have grown warmer.

Both the current study and Smith's own work suggest that it's likely "just a matter of time before the crabs move up onto the shelf," says Smith, who wasn't involved in Aronson's study.

The animals would likely devastate the region's invertebrates. Areas where king crabs live have much less sea floor life than areas where they haven't been found, both researchers note.

The crabs live in deeper areas adjacent to the shelf where it's a little bit warmer. Usually temperatures decrease in depth, but around Antarctica, slightly warmer waters are pushed down by a cold current that circles the continent, Aronson explains.

The king crabs (Paralomis birsteini) are found as shallow as 2,750 feet below the surface, on the continental slope. The shelf begins at about 1,800 feet below sea level, meaning the crabs would have to move up about 985 feet to reach the shelf. This species is capable of living in shallow waters; elsewhere it has been found at depth of 820 feet, Aronson says.

"The barriers for these predators are starting to evaporate," Aronson says.