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Images: The Evolutionary Puzzle of Seafloor Life

Giant clams up to 1 foot long thrive in the crevices around seafloor pillow lava, which vent hydrothermal fluids with chemical nutrients. This vent site on the Galápagos Rift, discovered in 2002, is called “Calyfield” after the clam (Calyptogena magnifica). (Photo by Tim Shank, Woods Hole Oceanographic Institution)

A cloud of flea-like crustaceans called amphipods hovers around tubeworms encrusted with limpets and mussels at the 9°N vent site in the eastern Pacific. (Advanced Imaging and Visualization Laboratory, WHOI; BBC Natural History Unit; Stephen Low Productions.)

Shrimps swarm at the Rainbow vent site in the North Atlantic. Shrimp populations grow larger at deeper vents. (Missão SEHAMA, 2002 (FCT/ PDCTM 1999 MAR/15281).)

Orange microbes coat the skeleton of a whale that fell to the seafloor off California. Craig Smith (University of Hawaii) and colleagues found that microbes decompose whale tissue and bones, producing hydrogen sulfide nutrients that sustain thriving animal populations. Whale-fall communities share many species with other chemosynthetic seafloor communities, such as hydrothermal vents and seeps, and may act as stepping-stones between them. (Craig R. Smith and Amy Baco.)

The Mid-Atlantic Ridge near the equator is offset by huge faults, called fracture zones, that are thousands of kilometers wide and tens of kilometers deep. A strong deep current flows along and through these fracture zones, almost straight across the South Atlantic. The combination of currents and fracture zones may act as a physical barrier blocking the transport of vent fauna between the North and South Atlantic Oceans—a subsea equivalent of a Berlin Wall. (Illustration by E. Paul Oberlander, Woods Hole Oceanographic Institution)

An Antarctic cruise in 2006 will search for the wreck of Ernest Shackleton’s ill-fated ship Endurance and test the theory that wooden wrecks play an important role in sustaining and dispersing seafloor populations.