Deepsea hydrothermal vent communities

In some areas of the eastern Pacific and Atlantic, hot springs or hydrothermal vents escape from volcanic fissures along the global system of mid-oceanic ridges (see Section 1.2.3) where sea-floor spreading occurs. Here water emerges from cracks and crevices at temperatures of up to 250°C. Even hotter vents exist where the water flows at up to 380°C from 'black smoker chimneys', formed from precipitated minerals.

In 1977, the manned submersible 'Alvin' explored one of these newly discovered vents, on the Galapagos rift near the Galapagos Islands. Scientists were dumbfounded by the discovery of a rich community of large animals living around the vent (Corliss and Ballard, 1977). The community is characterized by the red-plumed, tube-dwelling vestimentiferan worm, Riftia pachyptila, which can reach a metre or more in length. Giant-sized bivalve clams, crabs, shrimps, fish and even anemones have been described from these vents (Gage and Tyler, 1991).

Such communities have subsequently been discovered associated with vents at nearly all areas of tectonic activity so far explored in the deep Pacific and Atlantic. These 'oases' of life support up to 8.5 kg wet weight per square metre, in stark contrast to the almost barren rocky areas nearby. This raises the question of what energy source can support such rich communities in the deep sea where food is in short supply. It is now known that the basis of the food chain for these vent

Deep Sea Food Webs
Figure 6.2 Some connections of the marine food web.
Hydrothermal Vents Locations

Figure 6.3 Location of major known active hydrothermal vent sites. New vents are continually being discovered particularly along active ridge areas. Based on information from several sources. • = sites known to have vent biocommunities; A = unexplored sites.

Figure 6.3 Location of major known active hydrothermal vent sites. New vents are continually being discovered particularly along active ridge areas. Based on information from several sources. • = sites known to have vent biocommunities; A = unexplored sites.

animals is chemoautotrophic bacteria. These bacteria 'feed' on sulphur-containing inorganic compounds, and chemosynthesize organic carbon from elemental carbon dioxide and methane. The most successful vent animals, including Riftia, have developed symbiotic relations with these bacteria and so do not need particulate feeding mechanisms. Immense numbers of free-living bacteria provide a food source for other animals that are suspension and deposit-feeders. They in turn provide food for the larger scavengers and predators. These extraordinary deep-sea communities exist in permanent darkness and are entirely independent of light and photosynthetic products originating from the surface layers.

The lifetime of hydrothermal vents and their communities may be very short, a few decades, or very long depending on the rate of sea-floor spreading in the active region. Local communities of tubeworms, destroyed by fresh lava eruptions, can regrow within 2 to 3 years (Lutz and Haymon, 1994). Vents and vent fields are often separated by hundreds of kilometres and the question of how new vents are colonized is still being studied. Biologists at the Plymouth Marine Laboratory (UK) are studying larval DNA of vent animals to help trace their dispersal and relationships with populations elsewhere. American scientists have discovered species of animals normally only associated with vents, on whale carcasses on the deep-sea bed. They speculate that these carcasses provide ephemeral stepping-stones which allow animals to cross more easily between vents. However, recently it has been discovered that in some areas, such vents are very common and can be found at distances of only 20 miles or so apart. In these cases, spread from one vent to another would be relatively easy.

An excellent account of hydrothermal vents and their associated communities is given in Gage and Tyler (1991) and German et al. (1996) who also site further useful references.

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Responses

  • milly
    Why are hydrothermal vents helpful to the deep sea ecology?
    8 years ago
  • liberato
    What is the lifetime of a thermal vent community?
    8 years ago
  • kathryn
    Are the hydrothermal vents entirely independent of surface photosynthetic producers?
    8 years ago
  • mathilda
    Are hydrothermal vent communities entirely independent of surface photosynthetic production?
    6 years ago
  • lena
    What is the lifespan of hydrothermal vent communities?
    3 years ago

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