Scientists
have discovered bacteria living on the sea floor that don't need light to
live. It's thought that these bacteria originate below the sea floor,
where they live under very high temperatures and pressures. It's also thought
that they make up more living matter than do all of the other living creatures
on Earth combined -- in
the water and on land.
Dr.
Stephen Hammond of the VENTS program of the National Oceanic and Atmospheric
Administration described the discovery of these bacteria in the 1970s as
comparable to finding an undiscovered tropical rain forest. He said there's just as much diversity of species
among the bacteria.
The
bacteria form the foundation of an entire ocean ecosystem. They live inside the tissues of
giant tube worms -- which can grow to nearly three meters long. Fish eat
the worms, and, in turn, become food for larger fishes and so on. The
worms are filled with the bacteria. There are more bacteria living in just one
ounce of worm tissue than there are people living on Earth. The worms and the
bacteria help feed each other. A worm's bloodstream carries nutrients to the bacteria. In return, the
bacteria create waste products that feed the worm.1
Introduction
to the Pogonophora
Weird tube worms of the deepest seas
In
1900, a strange tube-dwelling worm was dredged from deep waters around
About
80 pogonophoran species are
known today, with new species still being discovered. One of the most
spectacular zoological discoveries of recent years was the finding in 1977 of
giant pogonophoran worms,
1.5 meters long, growing in heated, sulfur-rich water around warm-water vents
in the
The
name Pogonophora is Greek
for "beard-bearers," and comes from the fact that many species have
from one to many tentacles at the anterior end. These tentacles somewhat
resemble the lophophore
found in animals like brachiopods and bryozoans, as well as the feeding
tentacles of certain chordates. The incompletely known anatomy of pogonophorans was interpreted to
show that pogonophorans
were chordate relatives. Because pogonophorans
live with their lower ends buried in mud, and were broken during the dredging
process, it was not until 1964 that a complete pogonophoran was recovered. It turned out that pogonophorans have a segmented
posterior end of the body -- the opisthosoma
-- that bears setae and resembles an annelid body. The forward part of the
body, or prosoma, is unsegmented. Because of the
segmented opisthosoma, and
because pogonophoran larvae
have been found to look very much like annelid larvae, pogonophorans are now considered to be close
relatives of the annelids.
How
do pogonophorans feed with
no mouth or gut? Some nutrition is provided by absorbing nutrients directly
from the water with the tentacles. But most of a pogonophoran's nutrition is provided by symbiotic
bacteria living inside the worm, in a specialized organ known as the trophosome that develops from the
embryonic gut. Inside the trophosome,
these bacteria oxidize sulfur-containing compounds such as hydrogen sulfide,
which pogonophorans absorb
through their tentacles -- the bright red color of rift-dwelling pogonophoran tentacles is due to
hemoglobin, which absorbs both sulfides and oxygen for the use of the bacteria.
The bacteria derive energy from sulfur oxidation, which they use to fix carbon
into larger organic molecules, on which the pogonophoran feeds.
The
fossil record of pogonophorans
may extend back to the Vendian
Period; long thin tubes known as sabelliditids
have been found in rocks of that age,
and somewhat resemble pogonophoran
tubes. However, studies on sabelliditid
structure have proved inconclusive in determining exactly what these fossils
were. A few fossil pogonophoran-like
tubes have turned up in later deposits (e.g. Adegoke 1967), but pogonophorans are generally quite rare as fossils.
2
Creatures
of the Thermal Vents
by Dawn Stover
The
three-person submersible Alvin sank through the cold, dark waters of the
Pacific Ocean for more than an hour, finally touching down on the sea floor
more than 8,000 feet below the surface. It was December 1993, and the
scientists inside the sub had come to this stretch of the East Pacific Rise, an
underwater mountain range about 500 miles southwest of Acapulco, Mexico, to
inspect a recently formed hydrothermal vent - a fissure in the ocean bottom
that leaks scalding, acidic water.
Peering out through the sub's tiny windows, the visitors were astonished to seethickets of giant tube worms,
some four feet tall. The tail ends of the worms
werefirmly planted on the
ocean floor, while red plumes on the other ends swayed like afield of poppies.
The giant tube worm is one of the most conspicuous members of a diverse
community that forms around hydrothermal vents. Scientists once thought that no
living thing could survive the harsh combination of toxic chemicals, high
temperatures, high pressures, and total darkness at these vents. But in 1977,
researchers diving in
Vents
form where the planet's crustal
plates are slowly spreading apart and magma is welling up from below to form
mountain ranges known as mid-ocean ridges. As cracks form at these spreading
centers, seawater seeps a mile or two down into the hot rock. Enriched with minerals leached from the rock, the
water heats and rises to the ocean floor to form a vent.
Vents
are usually clustered in fields, underwater versions of
The
largest vent field, called TAG (short for Trans-Atlantic Geotraverse), is
about the size and shape of a football stadium. Other fields have more
whimsical names like Clam Acres, Mussel Bed, Rose Garden, Garden of Eden,
Broken Spur, and Lucky Strike. Snow Blower is named for the white, flaky
bacteria discharged from its vents. Genesis is a vent that sputtered out but
came back to life a few years later.
Hydrothermal
vents are underwater oases, providing habitat for many creatures that are not
found anywhere else in the ocean. More than 300 new species have been
identified since the first vent was discovered in 1977.
Besides
the giant tube worms, which have so far been found only in the Pacific, there
are pencil-size Jericho worms with accordion-like tubes; orange worms covered
with tiny bristles; small benthic worms that wriggle through the mud; and
finger-length, dark red palm worms that stand upright, topped with wiglike fronds. A special class
of small worms, called Alvinellids
(named after the sub), live on the walls of mineral deposits that form around
vents.
Mussels,
shrimp, clams, and crabs are abundant at many vents, but these are not the same
species that you find in seafood dishes. The cocktail-size shrimp that dominate
vents in the mid-Atlantic, for example, have no eyes. However, at least one
species has an extremely sensitive receptor on its head that may be used to
detect heat or even dim light coming from vents. Scientists still aren't sure
how shrimp and other vent creatures cope with chemical-laden seawater that
would kill ordinary shellfish.
Biologists
have observed a variety of smaller crustaceans around vents, including
miniature lobsters called galatheids,
and amphipods resembling sand fleas. They have also seen snail-like limpets the
size of BBs, sea anemones,
snakelike fish with bulging eyes, and even octopuses.
While
octopuses are at the upper end of the vent's food chain, bacteria are at the
bottom. They are the first organisms to colonize newly formed vents, arriving
in a snowlike flurry and
then settling to form white mats or tendrils attached to the ocean floor.
Bacteria have been found living beneath the ocean's floor, and it seems likely
that they emerge from below when the conditions are right. Vent bacteria can
withstand higher temperatures than any other organism. That makes them
attractive to researchers who are developing heat-stable enzymes for genetic
engineering, and culturing bacteria designed to break down toxic
waste.
Water
pouring out of vents can reach temperatures up to about 400 C; the high
pressure keeps the water from boiling. However, the intense heat is limited to
a small area. Within less than an inch of the vent opening, the water temperature
drops to 2 C, the ambient temperature of deep seawater. Most of the creatures
that congregate around vents live at temperatures just above freezing. Thus
chemicals are the key to vent life, not heat.
The
most prevalent chemical dissolved in vent water is hydrogen sulfide, which
smells like rotten eggs. This chemical is produced when seawater reacts with
sulfate in the rocks below the ocean floor. Vent bacteria use hydrogen sulfide
as their energy source instead of sunlight. The bacteria in turn sustain larger
organisms in the vent community.
The
clams, mussels, tube worms, and other creatures at the vent have a symbiotic
relationship with bacteria. The giant tube worms, for example, have no
digestive system - no mouth or gut. "The worm depends virtually solely on
the bacteria for its nutrition," says microbial ecologist Colleen M.
Cavanaugh of
The
brown, spongy tissue filling the inside of a tube worm is packed with bacteria
- about 285 billion bacteria per ounce of tissue. "It's essentially a
bacterial culture," says Cavanaugh.
The
plumes at the top of the worm's body are red because they are filled with
blood, which contains hemoglobin that binds hydrogen sulfide and transports it
to the bacteria housed inside the worm. In return, the bacteria oxidize the
hydrogen sulfide and convert carbon dioxide into carbon compounds that nourish
the worm.
Tube
worms reproduce by spawning: They release sperm and eggs, which combine in the
water to create a new worm. Biologists don't know how the infant worm acquires
its own bacteria. Perhaps the egg comes with a starter set.
Scientists
also don't know how tube worms and other organisms locate new vents for
colonization. "The vents are small, and they're separated, like
islands," says Cindy Lee Van Dover, a biologist and
Studying
the life cycle of vent organisms is difficult. Researchers have visited only a
fraction of the ocean's hot spots. They have been able to observe vent life
only by shining bright lights on creatures accustomed to inky darkness, and
many specimens die quickly when removed from their unique environment.
Underwater cameras are helping scientists make less intrusive observations, but
diving expeditions are still the most useful way to gather information. The
1993
"The
most spectacular sight down there was this massive blinding snowstorm of
bacteria," says Rich Lutz, a marine ecologist at
Since
the eruption, scientists have been able to watch several stages of colonization
at the site. When they returned in March 1992, only a few bacterial mats
remained. In their place were colonies of
The
scientists first observed the giant tube worms at
During
a December 1993 dive to the
Another expedition is
planned for November. By then, the community of organisms now prospering at the
vents may already be a ghost town. When the flow of hot, sulfide-rich water
slows to a trickle, death also comes quickly.
2. Tube
1. Where was the giant tube worm found?
2. How do pogonophorans feed?
3. Where do bacteria get their energy?
4. How are shrimp around the vents different than the normal shrimp near the surface?
5. How hot is the water running out the vents? _______What about water about a foot away from the vent?
6. What is the most prevalent chemical dissolved in vent water?
7. How many bacteria are in an ounce of tissue?
8. How do tube worms reproduce?
9. What and where is Godzilla?
10. What happens when the vents stop flowing?