 
Riftia |
For nearly 25 years, scientists have wondered
how giant red-tipped tubeworms and other exotic marine life found at hydrothermal
vents on the deep sea floor get from place to place and how long their larva survive in a cold, eternally
dark place. Now Woods Hole Oceanographic Institution Biologist Lauren
Mullineaux and colleagues have helped answer those questions.
In a paper published May 3 in the scientific
journal Nature entitled “Larval Dispersal Potential of the
Tubeworm Riftia pachyptila at Deep-Sea Hydrothermal Vents”,
Mullineaux and colleagues provide the first direct answer to the questions
“How long can a vent larva live? And how far can it disperse?
Their work is part of the LARVE Project, funded
by the National Science Foundation, to understand how vent species maintain
their populations in changing vent environments, how they colonize new
vents, and what controls their distributions over regional and global
scales. The Nature paper is co-authored by Adam Marsh of the University
of Southern California, Mullineaux, Craig Young of Harbor Branch Oceanographic
Institution, and Donal Manahan of the University of Southern California.
Larval dispersal has been one of the major
questions in understanding how vent organisms colonize sites,” Mullineaux
says of the study. “Hydrothermal vents are constantly changing because
of frequent volcanic and tectonic activity related to the formation of
the earth’s crust. Although we have known for a while that larvae can
colonize new vent sites tens to hundreds of miles apart very quickly,
we’ve never understood how the larva of these animals disperse to do that,
or how long they can survive. Now we have some answers.”
Mullineaux and her colleagues studied the larvae
of the giant tubeworm Riftia pachyptila, a red-tipped worm that
can grow several feet in length and which lives in a white plastic-like
tube about an inch and a half in diameter. Specimens were collected from
the eastern Pacific at several locations. The team then successfully reared
embryos of the giant tubeworm to the larval stage under deep-ocean temperatures
and pressures and followed their early development using custom-designed
culture systems. They measured the metabolic rates of the larva at conditions
like those at the deep sea vents, 2° C (about 36° F) and 250 atmospheres
of pressure.
They found that a typical larva of Riftia
pachyptila could potentially survive for 38 days, just long enough
it appears to get to another active vent many miles away and colonize
it before running out of food.
But knowing the potential life span was only
part of the puzzle. How far could the larva go and survive? The answer,
it turns out, depends on where the vent is. At active vents, such as one
of the experiment sites at 9°50′ North on the East Pacific Rise off
Mexico, the hot waters mix with seawater to form buoyant plumes that rise
until they cool to neutral buoyancy at a distance of 175-200 meters (about
575 to 650 feet) above the ocean bottom. Many of the early life stages
of hydrothermal vent animals have been found trapped in this neutrally
buoyant plume. Local currents may then carry the plume great distances,
a sort of larval highway.
Since 1977 dozens of vent sites have been found
in the Atlantic and Pacific Oceans. Animal communities differ from site
to site, perhaps because of this larval highway and the nature of the
currents at the different vent locations. More than 500 species of animals
have been found at the known sites to date, many of them new species.
In August 2000, a Japanese team found the first
vents in the Indian Ocean. A team aboard the Woods Hole Oceanographic
Institution’s Research Vessel Knorr has just concluded the first
U.S. expedition to explore hydrothermal vents in the Indian Ocean. The
Knorr team has reported finding species of animals that appear
to be similar to those found in both the Atlantic and Pacific, but many
others that may be new species, raising the question again about how these
animals disperse or move around the globe.
Although no tubeworms have been found at the
Indian Ocean vent sites, Mullineaux says that could be because the larvae
can’t get there, or the Indian Ocean sites aren’t suitable, or perhaps
that vents with tubeworms just haven’t been found there yet.
Animal populations at different vent sites, in
appears, may have different dispersal limits based upon the local currents.
Mullineaux’s team says the life span of this species can now be used to
predict dispersal under the current conditions at other hydrothermal vent
sites.
“That’s a major step forward,” she
adds.” And it demonstrates the importance of scientists from many
disciplines working together to answer some very basic but fundamental
questions about how marine life on our planet survives.”
The LARVE Project (Larvae At Ridge
VEnts) is a component of the RIDGE (Ridge Inter-Disciplinary Global Experiments)
Initiative, a coordinated, interdisciplinary program aimed at understanding
the geology, physics, chemistry and biology of processes occurring along
the global mid-ocean ridge system.
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