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Another potential sign of global warming: Crabs are invading the shallow waters of the Southern Ocean

Numerous past posts have noted that evidence for global warming can be found in the numerous reports on specific environmental conditions and events around the globe (for example, the migration of corals around Japan, the trend in lakes around the world to become warmer).  Although these events and conditions may not support arguments made about the rate of change or general, global trends, they do manifest the reality of global warming.

A recent report on the Southern Ocean is just such an evidentiary bit.  Antartica is a wonderfully peculiar place.  Unlike most of the oceans of the world, its depths are warmer, at about 5 degrees C, than the shallows, which hovers between 0 degrees C and -2 C.  The result of this cold temperature in the shallows is that animals on the Antartic continental shelf have been free, for millions of years, from predators like crabs and sharks who cannot cope with the cold.  As a result (speaking of selection factors), sea lillies, brittle stars, giant ribbon worms, and molluscs have thin, soft shells, not the hard shells often seen elsewhere.

However, in the past couple of years, various researchers have spotted king crabs on the continental slope of Antartica.  This is marginal habitat for crabs, with an average temperature in the 1 to 5 degree C range.  When the temperature drops down to or below 1 degree C, crabs are unable to process magnesium ions.  Such ions, in large amounts, act as a narcotic and eventually kill the animal.  A recent survey in January 2011 found many king crabs in waters that were devoid of them in 2007. 

The key question, of course, is do the presence of the crabs reflect a warming of the waters, or the vagaries of sampling methodology.  Warming seems a real possibility.  Since records were kept, starting in the 1950's, the ocean west of the Antartic peninsula has warmed by 1 degree C.  The result is that a larger area is now habitable for the king crab.

Reports on these findings can be found at and