Living at Extremes
Menagerie at a hydrothermal vent.
by Peter Tyson
If there is a harsher place to live than a hydrothermal vent, it hasn't been
found yet. Pitch darkness, poison gas, heavy metals, extreme acidity, enormous
pressure, water at turns frigid and searing—this seafloor environment seems
more like something from deep space than from our own deep sea.
Yet amazing communities of life exist at hydrothermal vents and the so-called
"black smoker" chimneys that, given the right conditions, rise above them like
erupting stalagmites. Blind shrimp, giant white crabs, and a variety of
tubeworms are just some of the more than 300 species of vent life that
biologists have identified since scientists first blundered upon this
otherworldly community two decades ago. More than 95 percent of these species
are new to science.
It's hard to say which is more remarkable to scientists studying this bizarre
world thousands of feet beneath the sea: what these animals have to cope with,
or what they have come up with to do that coping.
Sub illuminates smokers adorned with vent life.
Dark as night
For starters, it's pitch black at such depths. Sunlight penetrates no farther
than a few hundred feet down, leaving the deep-sea floor as dark as the deepest
With no sunlight, there are no plants; all vent life belongs to the animal
kingdom. And with no plants, there is no photosynthesis. Biologists were
flabbergasted when they first learned that creatures lived in total darkness at
the seafloor. All other life ever identified, on land or in the sea, derives
its energy either directly or indirectly from the sun. How, they wondered, did
these animals manage without?
Through chemosynthesis, it turns out. Vent species rely not on photons from
the sun but on chemicals from the Earth's interior. Tiny microbes oxidize the
hydrogen sulfide that diffuses out of the vents, providing nutrients for
animals higher up the food chain. Some creatures, such as the mollusks known as gastropod
snails, feast on the bacteria directly; others, including predatory fish, dine
on animals that have eaten or otherwise made use of the microbes; still others,
like tubeworms, host the microorganisms in their tissues in exchange for
organic compounds that the bacteria fashion from the vent chemicals and
seawater. (The only element from above that these microbes require for their
artistry is oxygen, which is abundant in seawater and was originally produced,
of course, by plants. So when it comes right down to it, even these life forms
ultimately rely on sunlight. Which likely made those flabbergasted biologists
breathe a little easier.)
A string of clams winds across a vent.
A toxic brew
As if utter darkness were not enough, vent animals must contend with a witch's
cauldron of deadly toxicants. Foremost among them is hydrogen sulfide, one of
the principal ingredients of the broiling water spewing from vents and black
smokers. While vent microbes thrive on the stuff, this gas is lethal to most
other organisms, including the creatures that live within wafting distance. Yet
not only do those animals survive it, they depend on it as intrinsically as
they do on the microbes. Hydrogen sulfide reacts spontaneously with oxygen, so
as soon as vent fluids come into contact with seawater, a swift reaction
occurs, releasing energy. All that energy would go to waste if it were it not
for the microbes. They harness that reaction and use carbon dioxide to make
organic compounds that tubeworms, for example, need to live.
Heavy metal and acid rock
Deep-sea anemone clings to lava outcrop.
Vents and smokers also release a bevy of heavy metals. Besides being toxic
substances, these particles can clog mouthparts and gills. Biologists are still
trying to figure out exactly how vent animals cope with these. Several animals
have metal-binding proteins in their systems, while others, like some
polychaete tubeworms, appear to expel these toxics in mucus. Beyond the toxic gas and
particles, vent water can also be extremely acidic. The pH of waters coming out
of black smokers can be as low as 2.8, making it more acidic than vinegar.
Biologists have seen "naked" snails around hydrothermal vents that could not
form their calcium carbonate shells because the water was too acidic.
Continue: Pressure's On
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