Coming
soon to a horror movie near you: Antarctica is being invaded by king
crabs
By
Philip Bump
13
December, 2012
The
Antarctic is being invaded by king crabs — and, somewhat
ironically, it’s because they survive better in warmer water.
From
Nature:
Cold
temperatures have kept crabs out of Antarctic seas for 30 million
years. But warm water from the ocean depths is now intruding onto the
continental shelf, and seems to be changing the delicate ecological
balance. An analysis by [marine ecologist Craig] Smith and his
colleagues suggests that 1.5 million crabs already inhabit Palmer
Deep, [a] sea-floor valley … And native organisms have few ways of
defending themselves. “There are no hard-shell-crushing predators
in Antarctica,” says Smith. “When these come in they’re going
to wipe out a whole bunch of endemic species.”
Scientists
are asking for volunteers to help stem the invasion; the research
team will provide melted butter and nutcrackers.
Crustaceans
like crabs and lobsters have a strange reaction to particularly cold
water.
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.
As
ocean temperatures have risen, so have temperatures in the Palmer
Deep.
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 metres down in the Southern Ocean up over the lip of the
continental shelf.
[A]s
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 kilometres of warm water wafts up
from that collision, spilling onto the continental shelf. The same
thing happens elsewhere, says [oceanographer Douglas] 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. …
Average water temperatures west of the Antarctic Peninsula have risen
by 1 °C in the past 50 years, and continue to rise by 0.01–0.02 °C
per year.
And
that warmer water means crabs can now better survive, stepping into
an ecosystem unable to protect itself against the invasion.
The
grimmest part of the story, though, may be this quote from Florida
Institute of Technology marine biologist Richard Aronson.
“Every
time we make a prediction of what we think will happen in the next 50
years, then poof, 10 years later, there it is,” he says. “So I
think this is going to be happening more rapidly than, as
conservative scientists, we’re used to predicting.”
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