Hydrothermal vents, or
hot vents as they are often called, were first
predicted to exist in the 1970s. Scientists predicted that
hot springs were likely to exist at the
rifts in the
ocean floor where
tectonic plates were moving apart to form new
ocean bed; the hot
magma welling up to fill in the gaps, so to speak.
The first
site with
hydrothermal vents was discovered in 1977, on the
Galapagos Rift off the
coast of
Ecuador, at a
depth of 2500
meters. This discovery was expected. What came as a total surprise, however, was the
abundance of life that surrounded the hydrothermal
vents. The makeup of the
communities centered on these vents was also extremely unexpected, consisting of
sea life that had never before been seen -
giant tubeworms, huge
clams,
mussels and
crabs. And all of this abundance in extremely
stark contrast to the normally close to
barren sea floor.
Since this first discovery numerous other sites have been found in
oceans around the
globe. These sites have been, and still are, the subject of intensive study, new additions to the
tree of life being found on a nearly weekly basis. And the wonder hasn't left the field of
benthic studies yet. The discovery of an extensive site on
December 5, 2000, in the
Atlantic Ocean, led
Margaret Leinen,
National Science Foundation assistant director for
geosciences to say the following:
The first non-photosynthesis based ecosystem
Studies have shown that most of the hydrothermal vent
ecosystems exist through an intricate
symbiotic system, wherein some of the larger organisms (like the
tubeworms) are
host to
hydrogen sulfide-oxidizing bacteria. These
bacteria form the base of the ecosystem's
food chain, much like plant life forms the
base in all other known ecosystems (up to now, at least). Plants do this through
photosynthesis, the process whereby they convert CO
2 (
carbon dioxide) and H
2O (
water) into O
2 (
oxygen) and C
6H
12O
6 (
sugar, or
energy). Up until the discovery of the
life forms surrounding these vents, this was thought to be the only way for organisms to 'create' energy
1.
The
bacteria that provide the energy for the hydrothermal vent ecosystems use (mostly) H
2S (
hydrogen sulfide, the
gas that smells like
rotten eggs) to produce their sugars. This type of sulfur-oxidizing bacteria, and other forms of bacteria that gain energy from the
metabolism of
inorganic compounds, belong to the
category of organisms called
chemoautotrophs. These bacteria
oxidize2 compounds like hydrogen sulfide and store energy in the form of
ATP (
adenosine triphosphate), which is the universal 'energy'
molecule in all organisms. These bacteria then use this energy to convert carbon dioxide into simple sugars and other molecules, just like plants. This process has been named
chemosynthesis, as opposed to the
photosynthesis done by plants.
Since the first discovery of chemosynthesis at these hydrothermal vents, studies have shown bacteria - often
extremophiles - in other
niches of
nature to
utilize chemosynthesis for their energy needs.
Symbiosis and plain old eat and be eaten
While some of the life forms directly utilize the energy produced by the
chemoautotrophs, by eating them (as some of the
species of
crab have been seen to do), others maintain a more
friendly relationship with these bacteria. The tubeworm is probably the
prime example of this (or maybe just the most intensively examined one). The
tubeworms have a peculiar body, in that they have no
digestive tract whatsoever. No
gut, no
mouth, and no
anus, which on first inspection is strange, as they
grow to be over a meter in length. If they can't eat, how do they
survive and grow?
A
graduate student at
Harvard University,
Colleen Cavanaugh, came up with the answer. Inside the body of the tubeworm is an
organ called a
trophosome. The trophosome is highly
vascularized and contains specialized
cells packed full of
chemoautotrophic sulfur bacteria. By means that are not entirely understood, the tubeworm provides all the
chemicals necessary for the bacteria to make
food, including sulfur,
oxygen, and
carbon dioxide, and the bacteria
manufacture sugars or some other form of energy-rich molecules that provide
nutrition to the tubeworm. The
blood-red hemoglobin that fills the tubeworm's
cardiovascular system is almost certainly important in the
transport of sulfur and oxygen. How this is accomplished and how nutrition is provided to the tubeworm from the bacteria is less well understood.
Other
vent organisms use similar
symbiotic mechanisms to obtain their nutrition. As stated, others simply
feed on the sulfur bacteria directly. The larger organisms, such as some types of
crab and
fish, are most likely feeders living on other living or dead vent organisms. Thus, a
food chain is established, consisting of
primary producers (chemoautotrophic sulfur bacteria), the
secondary producers (tubeworms,
mussels,
clams,
shrimp), and
predators (fish) or
detritivores (crabs).
Implications for other disciplines
One of the more
profound impacts of all these wonderful
discoveries is that
science has been made to see that
there are indeed more roads that lead to Rome.
Rome being, in this case,
life itself. It was always thought that the
basis for life could only
exist where some
essential ingredients were in supply, two of those being
water and
sunlight. Now, with the discovery of hydrothermal vents, one example is known where life
spurned one
ingredient once thought essential.
One of the
fields this has made an impact on, is
extra-terrestrial science. The people at
NASA and their
colleagues are now cautiously considering the possibility of life on, for example, a number of
moons of
Jupiter, like
Io,
Ganymede and
Callisto. The last two apparently have
liquid oceans (and, it follows, are heated
internally in some way), while the first, Io, is one of the most
volcanically active bodies in our
solar system. If life can so thoroughly
surprise us on our own
planet, maybe it's possible it'll put an effort into surprising the hell out of us somewhere outside our
atmosphere?
Sources:
http://pubs.usgs.gov/publications/text/exploring.html
http://www.nsf.gov/od/lpa/news/press/00/pr0093.htm
http://www.oceansonline.com/hydrothe.htm
1 Out on a limb here. Not entirely sure this was the first instance of such a discovery
2 That is, they remove electrons from the compounds
September 21, 2001