FAQ supplement: the tube worm BBQ

1979 - 1st black smoker vents (350°C) discovered at 21°N on the intermediate-spreading East Pacific Rise

1981 - vents discovered on the intermediate- spreading Juan de Fuca Ridge off Oregon/Washington

1982 - vents discovered in the sedimented Guaymas Basin, Gulf of California

1984 - 1st low temperature (methane) seep community discovered on a subduction zone (Cascadia) instead of a mid-ocean ridge

1985 - vents discovered on the slow-spreading Mid-Atlantic Ridge; seeps discovered at Japan and Peru-Chile subduction zones (trenches)

1987 - vents discovered on a spreading center behind a subduction zone in Marianas Basin (near Guam)

1993 - discovery of shallowest known vent community (1000 m depth) at Lucky Strike on slow-spreading Mid-Atlantic Ridge

• The findings of unusually dense populations of animals in the deep sea, clustered around hydrothermal vents, was originally a puzzling discovery. As anywhere else on earth, animal life in the deep sea was known to be sustained by plants; mainly by phytoplankton of surface waters. These photosynthetic primary producers of organic carbon from carbon dioxide (CO₂) form the base of the food chain. However, only a small fraction of the total organic matter produced escapes recycling in surface waters and further decomposition in the water column by sinking relatively quickly as particulate material to the bottom. So in principle, the deeper the bottom, the fewer the food particles arrive, and consequently, the smaller the benthic animal biomass.

• In light of this, the biomass of the vent communities discovered on the seafloor was much too high. Its quantity and distribution suggested a food source other than organic particles trickling down from the surface. The dense clusters of mussels, clams, and tubeworms around vent openings indicated a highly localized food source. When hydrogen sulfide was found to be a substantial constituent of the fluids emitted from these vents, the possibility of chemosynthetic primary production of organic carbon became apparent. Today, after several years of work at the vents and in the laboratory, this hypothesis is accepted as fact.

• Whereas on the surface, photosynthesizing bacteria are the base of the food chain, on the deep seafloor it is chemosynthesizing bacteria:

  CO₂ + 4H₂S + O2 = CH₂O + 4S + 3H₂O

  carbon dioxide & hydrogen sulfide ---> organic carbon & sulfur (chemo)

  carbon dioxide & light ---> organic carbon & oxygen (photo)

• In April 1991, a team of scientists visiting the fast-spreading East Pacific Rise (EPR) at 9°N was the first to witness the near aftermath of a deepsea eruption. This event wiped out many of the existing vent communities in the region. On return visits in ‘92, ‘93, and ‘94 scientists documented the phoenix-like rebirth of hydrothermal vent communities.

• Alvin divers to the EPR on April 14, 1991 witnessed fresh lava shards on the seafloor dusted by fine gray ash, which they later learned was less than 2 weeks old. Dead tubeworms were scattered about like spent firecrackers. Since the specimens carried to the surface had freshly charred flesh, the site was dubbed Tubeworm Barbecue.

• Many areas near Tubeworm Barbecue were blanketed by acres of thick, white mats of bacteria in 1991. A year later, brachyuran crabs had arrived and eaten most of the bacteria away. Giant tubeworms had recolonized the eruption site and grown to a length of over 4 feet.

• By 1993 most of the tubeworms in some areas were dead or dying, starved by the shutdown of the vents. Only jellyfish-like siphonophores, nicknamed "dandelions" were alive. These animals, about the size if ping-pong balls, shoot minute stinging tentacles into the current to capture food.

• Another eruption may occur this year and kill these communities off again. Living in this dangerous and unstable environment, all vent fauna are governed by the dictum: live fast, die young.

• Scientists studying the 9°N segment of the EPR have discovered 300 new species of animals. Many questions remain unanswered, such as exactly how do tubeworms, which have no structures for swimming or crawling, colonize the vents?? How do all of these vent creatures survive in conditions that would resemble a toxic waste site??