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Predatory invasions due to warming
threaten Antarctica's marine life
Feb 15, 2008
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Climate
change is causing a major upheaval in the shallow marine ecosystems
of
Antarctica. Predatory crabs are poised to return to warming
Antarctic waters
for the first time in millions of years, which will disrupt the
composition of
the archaic marine communities.
“Antarctic marine communities are functionally Paleozoic,” says
paleobiologist
Rich Aronson of the Dauphin Island Sea Lab in Alabama. “They look
like
primeval communities from hundreds of millions of years ago because
modern
predators—crabs and fish—are missing.”
But this long stable situation is about to change. “The crabs are on
the
doorstep; they are sitting in deep water, and only a couple of
hundred
bathymetric meters now separate them from the slightly cooler
shallow water in
the Antarctic shelf environment,” says Sven Thatje of the National
Oceanography Centre, Southampton in the UK.
Thatje, Aronson and Cheryl Wilga of the University of Rhode Island
will
discuss their findings at the American Association for the
Advancement of
Science (AAAS) meeting in Boston, MA at a press conference on
Friday, February
15, at 12:00pm noon EST when AAAS and the Ecological Society of
America will
also co-release a new Ecology paper by Thatje and coauthors.
Marine life on the Antarctic seafloor is unique. Nowhere else do
giant sea
spiders and marine pillbugs share the ocean bottom with fish that
have
antifreeze proteins in their blood. The shell-cracking predators
that dominate
bottom communities in temperate and tropical waters have been shut
out of
Antarctica because it is simply too cold for them. They have been
physiologically barred from entry.
“Crabs have a problem in cold water,” says Thatje, “They cannot
flush
magnesium out of their blood, so when they are already moving slowly
because
of the cold, the magnesium makes them pass out and die.”
Magnesium is a narcotic for marine invertebrates. “My zoology
students
routinely use magnesium sulfate—Epsom salts—to anesthetize
invertebrates so we
can study them,” Aronson adds.
Fast-moving, bone-crushing crabs, fish, sharks and rays are keystone
predators
in most places, but they cannot operate in the icy waters of
Antarctica. The
only fish there—the ones with the antifreeze proteins—eat small,
shrimp-like
crustaceans and other soft foods. The main bottom dwelling predators
are
slow-moving sea stars and giant, floppy ribbon worms.
Because crabs and predatory fish are not speeding around the
seafloor smashing
clams, snails and other animals with hard skeletons, marine food
webs are
different in Antarctica. Released from the dangers of predation,
filter
feeders such as brittlestars thrive in dense populations.
Antarctica began to cool off around 40 million years ago. Aronson
and a team
of paleontologists collected the abundant marine fossils found at
Seymour
Island off the Antarctic Peninsula. Linda Ivany of Syracuse
University
reconstructed changes in the Antarctic climate from chemical signals
preserved
in ancient clamshells. And Aronson discovered that, as temperatures
dropped
and crabs and fish were frozen out, the slow-moving predators that
remained
could not keep up with their prey. Filter feeders flourished in this
new
environment. Snails, once out of danger, gradually lost the spines
and other
shell armor they had evolved against crushing predators.
During the ice ages, conditions were even more harsh than usual for
Antarctic
sea life. According to Thatje’s new study, life hung by a thread.
Remnants of
marine communities huddled beneath open, ice-free areas called
polynyas in the
vast, frozen wasteland that covered the Southern Ocean. Whales,
seals, and
penguins had to migrate northward to survive. When the ice retreated
about
12,000 years ago, the Antarctic fauna once again spread out along
the coast.
These new insights are important to understanding how life is able
to cope
with climate oscillation and current global warming.
Now, coastal waters in Antarctica are warming rapidly. Temperatures
at the sea
surface off the western Antarctic Peninsula went up 1°C in the last
50 years,
more than double the global average. As temperatures rise, magnesium
poisoning
becomes less of a barrier to crabs.
In January of 2007, Thatje and a group of oceanographers from the UK
discovered that crabs are massing in deeper, slightly warmer waters,
ready to
conquer the Antarctic shallows. If the crabs’ invasion succeeds,
they will
devastate Antarctica’s spectacular Paleozoic-type fauna and
fundamentally
alter its ecological relationships.
“That would be a tragic loss for biodiversity in one of the last
truly wild
places on earth,” says Aronson. “Unless we can get control of
greenhouse-gas
emissions, global warming will ruin the marine life in Antarctica
and make the
world a sadder, duller place.”
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Contact Information
Cheryl D. Wilga
Associate Professor
University of Rhode Island
Rhode Island, USA
+1 401 874 9020
cwilga@uri.edu
Sven Thatje
Lecturer
National Oceanography Centre, Southampton
University of Southampton
Southampton, UK
+44 (0)23 8059 6449
svth@noc.soton.ac.uk
For outside commentary on this story:
James B. McClintock
Professor, Department of Biology
University of Alabama at Birmingham
+1 205 475 2525
mcclinto@uab.edu
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