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Invasion of the Lithodid Crabs: They're Coming! ... Or Are They?
Volume 16, Number 52: 25 December 2013

In introducing their intriguing new study, Griffiths et al. (2013) write that "in recent years, the 'crab invasion' story has become a metaphor for climate change in the Antarctic marine realm, both in scientific literature and the media." The underlying premise of this hypothesis is that crabs were driven out of Antarctica between 40 and 15 million years ago, and that they are just now "returning as similarly 'warm' and favorable habitats become available once more."

This "invasion hypothesis," as the five British scientists describe it, is said by them to be "based on a geographically and spatially poor fossil record of a different group of crabs (Brachyura), and examination of relatively few recent lithodid samples from the Antarctic slope." So, in an effort to gain more specifically relevant and voluminous information, they examined the existing lithodid fossil record, as well as the distribution and biogeographic patterns of the more than 16,000 records of recent Southern Hemisphere crabs and lobsters. And what did they find?

Griffiths et al. found that "globally, the lithodid fossil record consists of only two known specimens, neither of which comes from the Antarctic." And they add that "recent records show that 22 species of crabs and lobsters have been reported from the Southern Ocean, with 12 species found south of 60°S," all of which "are restricted to waters warmer than 0°C, with their Antarctic distribution limited to the areas of seafloor dominated by Circumpolar Deep Water," which currently "extends further and shallower onto the West Antarctic shelf than the known distribution ranges of most lithodid species examined." And thus they conclude that "geological evidence suggests that the West Antarctic shelf could have been available for colonization during the last 9,000 years."

As a result of these several findings, the five British Antarctic Survey scientists concluded that "distribution patterns, species richness, and levels of endemism all suggest that, rather than becoming extinct and recently re-invading from outside Antarctica, the lithodid crabs have likely persisted, and even radiated, on or near to the Antarctic slope." And they thus and quite simply affirm that "there is no evidence for a modern-day 'crab invasion'."

Sherwood, Keith and Craig Idso

Griffiths, H.J., Whittle, R.J., Roberts, S.J., Belchier, M. and Linse, K. 2013. Antarctic crabs: Invasion or endurance? PLOS ONE 8: e66981.