Strange Underwater Tower Off California

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Siboglinids (left), which lack a mouth and digestive system, live inside tubes (right) in methane or sulfide-rich environments. Scripps Institution of Oceanography
Scripps Institution of Oceanography

THE GIST

- Methane leaking out of the seafloor is hosting an ecosystem of strange creatures off San Diego.

- The chemosynthetic animals include thread-like tubeworms called siboglinids that have no mouth or digestive system.

While mapping the seafloor off San Diego, researchers found something odd: a seafloor mound about the height of a two-story building and the size of a city block.

Further investigation found evidence the formation was caused by methane leaking out of the seafloor, which would make it the first so-called "methane seep" in San Diego County, the Scripps Institution of Oceanography at UC San Diego announced yesterday (July 25).

The Scripps researchers took samples from 3,400 feet (1,036 meters) below the surface and bought up strange worms and clams that likely live off symbiotic bacteria that break down the clear, flammable gas.

Such sites are important oases of life on the dark seafloor, with the methane-eating bacteria at the base of a rich and productive community that helps sustain the surrounding deep-sea ecosystem.

"These chemosynthetic ecosystems are considered 'hot spots' of life on the seafloor in an otherwise desert-like landscape," said expedition member Alexis Pasulka, a Scripps biological oceanography graduate student, in a statement. "New forms of life are continuously being discovered in these environments."

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Organisms collected from the newly discovered site include thread-like tubeworms called siboglinids and several clams. Siboglinids lack a mouth and digestive system and gain nutrition from a symbiotic relationship with bacteria living inside them, while many clams at seeps get some of their food from sulfide-loving bacteria living on their gills.

The scientists found the site 20 miles (32 kilometers) west of Del Mar, Calif. It's centered on a fault zone known as the San Diego Trough Fault zone. Methane, or natural gas, exists in the Earth's crust under the seafloor along many of the world's continental margins. Faults can provide a pathway for methane to "seep" upward toward the seafloor.

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Methane is a potent greenhouse gas, and researchers don't yet fully understand the magnitude to which seeping methane in the ocean contributes additional carbon to the atmosphere. On many continental margins, so-called frozen methane hydrates could represent a future energy source. Along the West Coast, methane seeps are known to exist off Oregon, California (near Eureka, Monterey Bay, Point Conception and Santa Monica), in the Gulf of California and off Costa Rica.

The researchers will return to the site in December to study it further.

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