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The
tubeworm is one of the most recognizable and fascinating creatures
living at hydrothermal vents. It can grow to 8 feet tall. It moves
much like a lipstick — extending its crimson gills out of its tube
to sweep oxygen and sulfur from the water, and retracting the plume-like
structure when a hungry predator like the vent crab attacks.
The
tubeworm also is literally a “gutless wonder.” It has no eyes. It
has no mouth. It has no gut, or stomach. So how does the tubeworm
eat?
“The
tubeworm has a special partnership — a symbiotic relationship —
with bacteria,” says Dr.
Colleen Cavanaugh, Jeffrey Professor of Biology at Harvard University.
“Billions of bacteria live inside the tubeworm,” she notes. “The
worm provides these bacteria with a stable home, while the bacteria
convert the chemicals that shoot out of the vents into food for
the worm.”
Yet how does the tubeworm acquire the bacteria it needs for survival? Scientists have discovered that during its early life stages, the tubeworm has a mouth and gut for bacteria to enter. But as the worm rapidly grows, these features disappear!
After
riding the ocean currents for up to a month and sometimes hundreds
of miles, tiny tubeworms no larger than strawberry seeds “land”
at hydrothermal vent sites, and free-living bacteria begin colonizing
the tiny worms and making food for them.
Dr.
Cavanaugh wants to find out how this symbiotic relationship evolved.
During the Extreme 2003 expedition, she and her team will be collecting
bacteria from tubeworms, vent fluids, and rocks. The samples will
be analyzed using molecular techniques to help reveal their origin
and history.
“How
did the tubeworm and its bacteria decide they would be partners?
How did they agree to cooperate with each other rather than eat
each other?” she asks. “Solving this mystery will help us make tremendous
strides in understanding the ecology of vent communities.”
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 Resembling
giant lipsticks, tubeworms (Riftia pachyptila) live over a mile
deep on the Pacific Ocean floor near hydrothermal vents. They may grow
to about 3 meters (8 ft) tall. The worms' white tube home is made of a
tough, natural material called chitin (pronounced "kite-in").
Tubeworms
have no mouth, eyes, or stomach ("gut"). Their survival depends
on a symbiotic relationship with billions of bacteria
that live inside them. These bacteria convert the chemicals spewing out
of the vents into worm food. This chemical-based food-making process is
known as chemosynthesis.
The
bright-red plume is the tubeworm's breathing apparatus. The blood in it
contains special forms of hemoglobin that have a super-high affinity for
the oxygen in the seawater. Masses of tubeworms, with their showy plumes,
inspired scientists to name one vent field "The Rose Garden"
in 1979.
However,
during an expedition that began in May 2002, scientists from Woods Hole
Oceanographic Institution and NOAA's Ocean Exploration Program found that
"The Rose Garden" may have been covered over with lava from
a recent volcanic eruption. They found a thriving new site nearby that
they named "Rosebud." For more details, read the story
on the Woods Hole Web site.
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When
tiny tubeworm larvae
settle down at new vent sites, they grow rapidly and reproduce because
when a vent shuts down, the vent animals cannot survive. This tubeworm
species, Riftia pachyptila, may grow to about 3 meters
(8 ft) tall. It has
no mouth, eyes, or gut (stomach). Its survival depends on the bacteria
that live inside it. They make food for the worm from the vent's
toxic chemicals.
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