Rapid warming of the ocean west of the Antarctic Peninsula–the part of the continent that extends north toward South America–makes it possible king crab populations could return from the deep sea to the relatively shallow continental shelf, where they could become high-level predators and disrupt the ecosystem, according to National Science Foundation (NSF)-funded researchers.
The researchers’ results will be published Sept. 30 in Proceedings of the National Academy of Sciences.
In the 2010-2011 Antarctic summer (which lasts from October to February, the opposite of summer in the Northern hemisphere), researchers used a camera sled towed by the NSF research vessel Nathaniel B. Palmer to document for the first time a reproductive population of king crab on the continental slope off Marguerite Bay. The slope is located on the western Antarctic Peninsula, adjacent to the continental shelf, at depths between 2,700 to 7,200 feet (840 to 2,200 meters).
Although the waters nearer the surface currently remain too cold for the crabs to survive, the researchers found no barriers–including salinity levels, the types of sediments on the sea floor or temperatures–that would prevent the creatures from eventually emerging onto the shallower outer shelf, in water that ranges from 1,300 to 1,800 feet (400 to 550 meters) in depth.
“Because other creatures on the outer shelf have evolved without shell-crushing predators, if the crabs moved in they could completely restructure the ecosystem,” said lead author Richard Aronson, of the Florida Institute of Technology (FIT).
The study provides initial data and does not by itself prove that crab populations will expand into shallower waters.
“The only way to test the hypothesis that the crabs are expanding their depth-range is to track their movements through long-term monitoring,” said study author, James McClintock of the University of Alabama at Birmingham (UAB).
The Division of Polar Programs in NSF’s Geosciences Directorate supported the research through collaborative awards to Aronson and McClintock. The Division manages the U.S. Antarctic Program, through which it supports all U.S. government research in Antarctica and aboard ships in the Southern Ocean.
An Antarctic expedition run jointly by NSF, the Swedish Polar Research Secretariat, and the Swedish Research Council collected the data used in the study. The expedition included scientists from FIT, UAB, the Woods Hole Oceanographic Institution, the University of Gothenburg in Sweden, and the University of Southampton in the United Kingdom.
Water and air temperatures along the western Antarctic Peninsula have been increasing at a rate far exceeding the rest of the continent, making it one of the most rapidly warming places on the planet. In the paper, the researchers note that at present rates of warming the crabs should be able to survive in coastal environments (waters shallower than 650 feet, or 200 meters) within the next several decades.
Some predators, such as the Antarctic toothfish and Weddell and elephant seals, could feed on the crabs if they were to colonize the shallower waters. But the vulnerable smaller creatures that currently live in the shallows would remain easy prey for the crabs.
The overall effect of the migration of king crabs to shallower waters, explained FIT postdoctoral scientist and co-author Kathryn Smith, would be to make the currently unique Antarctic ecosystem much more like ecosystems in other areas of the globe.
Such changes, the researchers conclude, would fundamentally alter the Antarctic sea-floor ecosystem and diminish the diversity of marine ecosystems globally.
Aronson said that, based on his previously publish research, it is likely that crabs haven’t played a role in the shelf ecosystem for millions of years.