A world without light
On February 17, 1977, a team of scientists in the deep-sea submersible Alvin descended 2,500 meters into the Galápagos Rift, a boundary between tectonic plates. They were searching for predicted underwater hot springs, but what they found was completely unexpected. In the near-freezing 2-4°C water, they located vents shimmering with superheated fluid up to 350°C. Surrounding these vents was an oasis of life. The most striking organisms were clusters of giant tubeworms, Riftia pachyptila, with white tubes up to 3 meters long and bright red plumes swaying in the currents.
This discovery at the site, later named the Rose Garden, presented a deep puzzle. Photosynthesis, the process that uses sunlight to create energy, is impossible in this deep, dark environment. Scientists soon realized this entire food web was based on a different process: chemosynthesis. Instead of sunlight, the primary producers are bacteria that harness chemical energy from the vents, specifically from hydrogen sulfide. This finding changed the understanding of where and how life could exist on Earth. The expedition, which was initially a geological mission, had no biologists on board because no one believed complex life could survive in such conditions.
A symbiotic survival strategy
The giant tubeworm Riftia pachyptila has no mouth, no stomach, and no digestive tract. It survives entirely through a symbiotic relationship with bacteria living inside its body. The worm's body contains a specialized organ called a trophosome, which makes up a large portion of its internal volume and is packed with symbiotic bacteria. There are an estimated 285 billion bacteria per ounce of trophosome tissue.
The worm's bright red plume acts like a gill. It is filled with a unique form of hemoglobin that binds oxygen from the seawater but also hydrogen sulfide from the vents—a compound toxic to most other animals. This specialized blood transports the chemicals to the bacteria in the trophosome. The bacteria then perform chemosynthesis, oxidizing the hydrogen sulfide to produce organic carbon compounds that nourish both themselves and their host worm. This internal chemical factory allows Riftia pachyptila to have the fastest growth rate of any known marine invertebrate. Individuals can grow from a larval stage to 1.5 meters in less than two years.