THE GEOLOGY OF SEA-FLOOR MASSIVE SULPHIDES
23
Global distribution of
vent organisms
Hydrothermal vents with generally similar chemical/thermal
habitats exist in all of the world’s oceans. However, there are
significant differences among vent communities in different
regions of the world. For example, the giant tubeworms that
dominate many vent habitats in the eastern Pacific have nev-
er been seen at Atlantic, Indian Ocean, or southwest Pacific
vent sites. On the Mid-Atlantic Ridge, swarms of endemic vent
shrimp with chemoautotrophic symbionts cover many hydro-
thermal chimneys. In the Indian Ocean, shrimp, anemones,
and big, symbiont-containing snails constitute the largest
portion of the biomass. Analysis of the composition of vent
communities suggests at least five biogeographic provinces
for vent fauna, although the number and boundaries of these
provinces have yet to be resolved with any certainty (Van Do-
ver
et al
2002; Bachraty
et al
2009; Moalic
et al
2011; Rogers
et al
2012).
The scaly foot snails found at vents on the Central Indian Ridge
in the Indian Ocean have scales composed of iron sulphides
and are the only animals known to produce metal armour. Photo
courtesy of CL Van Dover.
Because of the myriad of adaptations necessary to live at hydrothermal vents, most animals cannot survive there. However, the
endemic vent fauna represent a source of evolutionary innovation not found elsewhere on earth. They often occur in extremely high
densities at hydrothermal vents. Giant tubeworms (Riftia pachyptila) from the East Pacific Rise are among the fastest growing animals
on earth. They have no mouth, gut, or anus and live their entire adult lives with one end of their bodies immersed in a hot tub and the
other in ice-cold water. They are not found in the southwest Pacific. Photo courtesy of IFREMER.
Shrimp on theMid-Atlantic Ridge and on Indian Ocean vents (Rimi-
caris sp) have lost their eyes but have evolved large light-sensing
patches on their backs to “see” the chimneys they call home. They
are not found in the southwest Pacific. Photo courtesy of IFREMER.
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