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Hydrothermal Vent Communities
(Released May 2006)

 
  by Carolyn Scearce  

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Early in the spring of 1991 a volcano erupted 2500 meters below the ocean's surface near hydrothermal venting sites at the northern portion of the East Pacific Rise. Prior to eruption, the sites, located over 4000 km SSW of Mexico's Pacific coast, hosted a thriving community. At hydrothermal vent sites, hot mineral rich water spews from the sea floor, and mixes with cold oceanic water. Vent chemistry provides the energy and raw materials with which microorganisms grow.
thick mat of tube worms
Vestimentiferan tube worms Riftia pachyptila from the East Pacific Rise
These microorganisms form the basis of the food chain in which unexpectedly high organism densities and growth rates are observed. Unique communities are formed around vents, attracting unusual creatures such as red-plumed giant tube worms and massive clams, which cluster around the dark chimneys where vent fluids emerge.

map of Pacific site
East Pacific Rise study site
In April of 1991, scientists conducting a site survey along the East Pacific Rise expected to find just such a community. Expedition members employed the services of Alvin, a submersible research vehicle with the capacity to carry a pilot and two passengers to a depth of 5 km. On April 4, members of the first dive found only fresh basalt and no signs of life. On a subsequent dive, conducted ten days later, a community was discovered that had been only partially covered by lava. Observers saw that some tubeworms were enveloped in obsidian, while others were cooked alive. Mussel shells were shattered and scattered all over the site (Lutz et al, 2001). Volcanic eruptions such as these not only kill off the organisms living in existing communities, but can alter the chemistry and reroute vent fluids (Mullineaux et al, 2003). In essence, an entirely new venting site replaces the previous one.

Alvin in the murky blue depths
Photograph of the submersible Alvin

As disturbing as the devastation was after the 1991 eruption, still, it provided biologists with a unique opportunity to observe the process of ecological succession occurring at newly formed hydrothermal vents. Scientists have been monitoring the East Pacific Rise site frequently since the eruption, documenting the process by which organisms colonize a new vent. Microorganisms first moved in, filling the water near the vents and also forming microbial mats on nearby surfaces. These abundant microorganisms attracted mobile vent fauna such as amphipods, copepods, and crabs. Vestimentiferan tube worms followed, replacing parts of the microbial mat. Later arrivals included crabs, mussels, and polychaete worms (Shank et al, 1998; Govenar et al, 2004). Associations between organisms are generally in flux during the initial 1-2 years of settlement, reaching maturity by approximately three years.

It can be a chancy life for organisms living at hydrothermal vents. Individual vent sites are extremely ephemeral on geological time scales, lasting only on the order of years to decades (Micheli et al, 2002). Volcanic eruptions can destroy whole communities, or vent fluids can cease to flow, slowly chilling and starving dependant communities. As vents wane, organismal associations can be observed slowly transitioning as they gain greater similarity to background communities (Tsurumi & Tunnicliffe, 2003). Mobile inhabitants may be able to escape from fading vent sites, but the large aggregations of sessile organisms die if fluids cease to flow. Organisms also face the standard biotic treats of predation and competition. Despite adversity, however, hydrothermal vent communities are among the most productive aquatic environments on earth, converting inorganic material into organic biomass at an unusually rapid rate.

Go To The discovery of hydrothermal vents

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