By WILLIAM J. BROAD, The New York Times
The deep seabed was once considered a biological desert. Life, the logic went, was synonymous with light and photosynthesis. The sun powered the planet’s food chains, and only a few scavengers could ply the preternaturally dark abyss.
Then, in 1977, oceanographers working in the deep Pacific stumbled on bizarre ecosystems lush with clams, mussels and big tube worms — a cornucopia of abyssal life built on microbes that thrived in hot, mineral-rich waters welling up from volcanic cracks, feeding on the chemicals that leached into the seawater and serving as the basis for whole chains of life that got along just fine without sunlight.
In 1984, scientists found that the heat was not necessary. In exploring the depths of the Gulf of Mexico, they discovered sunless habitats powered by a new form of nourishment. The microbes that founded the food chain lived not on hot minerals but on cold petrochemicals seeping up from the icy seabed.
Today, scientists have identified roughly one hundred sites in the gulf where cold-seep communities of clams, mussels and tube worms flourish in the sunless depths. And they have accumulated evidence of many more — hundreds by some estimates, thousands by others — most especially in the gulf’s deep, unexplored waters.
“It wouldn’t surprise me if there were 2,000 communities, from suburbs to cities,” said Ian R. MacDonald, an oceanographer at Florida State University who studies the dark ecosystems.