Two king crabs
Credit: © Katrien Heirman, Ghent University
King crabs, with their crushing claws and ecosystem-altering habits, have shown up in the warming waters of a deep basin in the Antarctic continental shelf, raising worries they'll hurt other species there.
"It looks like a pretty negative consequence of climate warming in the Antarctic," said Craig Smith, a professor of oceanography at the University of Hawaii at Manoa, who led the research into the new crab population, estimated at 1.6 million, in the Palmer Deep.
This species of crab, Neolithodes yaldwyni, is known to populate Antarctica's Ross Sea, which lies south of New Zealand. The Palmer Deep, a pocket in the relatively shallow continental shelf, lies south of South America. The discovery of a king crab population there suggests that, after millennia of apparently being held at bay by the cold water of the continental shelf, the crabs can now cross it.
The worry is that king crabs will threaten the unusual, isolated animal life established on the seafloor of the shelf. The research team saw evidence of this when they deployed a remotely operated vehicle to survey the Palmer Deep. While they found no evidence that the invasive species was living on the shallower, colder shelf, they warned that it could take hold there within two decades.
In the Palmer Deep, they saw that the crabs had disturbed sediment on the basin seafloor by digging for worms and other creatures, an alteration that affects other animals' habitat. The predatory crabs also feed on other invertebrates, like sea lilies and basket stars. These and other creatures were absent from depths below 3,117 feet (950 meters) where the crabs were found. [Image Gallery: Life at the South Pole]
The deeper the water, the warmer it is, the result of warmer water coming in from the north, Smith explained. The incoming water is saltier and denser, so it sinks below the cooler waters.
It appears the crabs are limited by temperatures approaching 34.5 F, though the team found crabs living in basin waters colder than 34.5 degrees Fahrenheit (1.4 degrees Celsius) and there is evidence that some members of this species can live at even colder temperatures.
The Palmer Deep is located near the West Antarctic Peninsula, an area experiencing rapid warming. Below 2,625 feet (800 m) in the Palmer Deep, temperatures have been increasing at a rate of about 0.018 degrees Fahrenheit (0.01 degrees Celsius) per year for almost 30 years.
Given the warming trend, these crabs could move up onto the shelf within one to two decades, according to the researchers.
The crab population in the Palmer Deep "is likely to serve as an important model for the potential invasive impacts of crushing predators," they write in most recent issue of the journal Proceedings of the Royal Society B.