As temperatures fell, the sea floor bloomed with soft-bodied echinoderms — invertebrates including starfish, brittlestars, sea lilies and sea cucumbers. At the same time, crush wounds caused by crabs or sharks on the arms of fossil starfish and sea lilies became rare — evidence that these predators were declining.
Crabs and lobsters were probably excluded by a physiological quirk. At temperatures below about 1 °C, they become unable to regulate magnesium in body fluids, leading to narcosis, clumsiness and paralysis of breathing. Most of the 100 or so fish species currently found on the Antarctic shelf belong to a single sub-order, whose members evolved antifreeze proteins to keep their blood flowing at subzero temperatures and then diversified to fill most niches in the frigid seas. They lack powerful jaws.
The result is an ecosystem reminiscent of that 350 million years ago, in which the top predators are slow-moving invertebrates such as starfish, sea spiders and ribbon worms. “All of this stuff has got a very Palaeozoic flavor to it,” says Aronson. The relaxation of natural selection allowed species to lose their natural armor, says James McClintock, a marine biologist at the University of Alabama at Birmingham. Animals on the Antarctic sea floor “are very weakly skeletonized”, he says. “You can pick up an Antarctic clam and crush it in your hand.”
By the mid 2000s, Aronson began to believe that if Antarctica's oceans warmed up, the ecological cascade that caused this blast-from-the-past ecosystem to flourish would run in reverse: crushing predators would return and wreak havoc. That prediction is now being tested.
Westerly winds are strengthening and the circumpolar current is intensifying, driven by atmospheric warming and a hole in the ozone layer over Antarctica. These changes are lifting warm, dense, salty water from 4,000 meters down in the Southern Ocean up over the lip of the continental shelf.
Douglas Martinson, an oceanographer at the Lamont–Doherty Earth Observatory in Palisades, New York, has documented this process on the western side of the Antarctic Peninsula, where crabs are invading. Martinson installed five temperature and current sensors around Marguerite Trough — a deep canyon carved into the sea floor by glaciers advancing to the edge of the continental shelf in past ice ages. The moorings captured an insidious process: as the circumpolar current skirts Antarctica's continental shelf, it runs head-on into the steep wall of the trough. About once a week, a swirling eddy containing 100 cubic kilometers of warm water wafts up from that collision, spilling onto the continental shelf. The same thing happens elsewhere, says Martinson: “It looks like this is what happens at all of the canyons that cut across the shelf.”
The temperature of this intruding water is only about 1.8 °C — but for an ocean region generally between 1 and −2 °C, the impact is substantial. And the incursion seems to have begun only recently, says Eugene Domack, a marine geologist at Hamilton College in Clinton, New York, who led the 2010 cruise to Palmer Deep.
Domack has managed to date the onset by measuring the amount of radioactive carbon-14 in deep-sea corals collected from the continental shelf — a process similar to reading tree rings. The corals had grown for 400 years before being dredged up. The carbon-14 content increased smoothly along the coral's growth axis for the first 350 years, and then dropped suddenly — indicating that the coral was being bathed in water with a reduced carbon-14 content. The water from the depths of the circumpolar current would fit the bill: it has been isolated from the carbon in the atmosphere for centuries. On the basis of these measurements, Domack has deduced that the warm-water incursion “kicked in somewhere around the turn of the last century, 1920 or 1930”.
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11 Comments
Add CommentBut...but I thought all global warming was based on flawed computer models by people who wanted to stay inside and make more computer models so I would have to shiver in the cold. Are you saying there are actual observations of change? /sarcasm
Reply | Report Abuse | Link to thisIn before the denialists...
Are these king crabs the same as caught in the northern waters for human food, If so then fishermen should be told that there is good fishing in the Antarctic and this might alleviate the menace some what,
Reply | Report Abuse | Link to thisI participated in the 2010 Antarctic research cruise and made a short film about the King Crab discoveries. It can be seen at www.crabnet.tv or at https://www.youtube.com/watch?v=cVNTfpDlPzE.
Reply | Report Abuse | Link to this“They're natural invaders, ... They're coming in with the warmer water.”
Reply | Report Abuse | Link to thisThe human species makes the water warmer and they are the invaders?
http://blogdredd.blogspot.com/2012/12/new-climate-catastrophe-criminality.html
King crabs are just one of many species shifting habitats, or rather shifting locals, as the climate changes. For instance, there is the lovely armadillo.
Reply | Report Abuse | Link to thishttp://mdc4.mdc.mo.gov/Documents/16308.pdf
I suspect the armadillo is having less impact that the king crabs are, but species shifts are not really a new thing. The effects of a changing climate are already under way.
Have Red Lobster lower the price on Crab Festival. Enlist the show Deadliest Catch. Problem solved.
Reply | Report Abuse | Link to thisOr, tell the Chinese King Crab helps with iron-rod erections. Problem solved twice.
Did these crabs move into these same waters during the last interglacial, when it was much warmer than now?
Reply | Report Abuse | Link to thisQuinn- LOL!
Comment by Carlyle on another article: "So although the West antarctic melted entirely 3 million years ago, the original authors claim the crabs MAY have been excluded for fourteen My, just for luck SIAM doubled it & then rounded up a further 2 My & when I challenged them they deleted my post. I hope you can begin to see that this is not aberant behaviour. It is typical. You can look up the Ice record for Antarctica yourself if you doubt me. There could even have been later melts & almost certainly numerous times that match the present."
Reply | Report Abuse | Link to thisI did not see the original post, but why would SA delete this?
There is an abundance of crab because we have killed most of their preditors, so there is no need for fishermen to go far to get crab.
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Reply | Report Abuse | Link to this1. SteveO
08:00 PM 12/12/12 writes...
......But...but I thought all global warming was based on flawed computer models by people who wanted to stay inside and make more computer models so I would have to shiver in the cold. Are you saying there are actual observations of change? /sarcasm...
Perhaps SteveO missed the comment in the article where Domack says the process started at the end of the Little Ice Age. (at the top of page 3 in the article)
The computer models referred to by SteveO such as the hockey stick put forth by Mann and others show that there was no such thing. Despite a multitude of historical references documenting said climate, people like Gore, Hansen and David Suzuki regularly use many computer models to show that _all_ climate variation in the last ten thousand years or so is anthropogenic.
The most amusing comment that I have read that justifies rejecting historical evidence in favor of computer models is the belief the Medieval Warming Period and subsequent Little Ice Age documentation was all part of a massive real estate scam run by the Vikings.(!!??!!)
http://evilbloggerlady.blogspot.com/2013/01/are-king-crabs-really-poised-to-kill.html Good comment. I linked it.
Reply | Report Abuse | Link to thisWhile I am skeptical of global warming alarmism, I do not want to see gentle sea pigs wiped out by giant crabs. I do not discount some global warming is taking place. It is, the planet is getting warmer (whether that is because of the natural cycles or is completely man made remains to be seen). But this has also happened in the past and I suspect these fluctuations in predator prey overlap in Antarctica have happened before too. But I would suggest we investigate further and see if that is the case (or not).