Strange Creatures of the Deep

By Frederic Golden

At 8,500ft., ocean life that does not depend on the sun

In 1977, while exploring an area of hot volcanic geysers on the Pacific Ocean floor near the Galapagos Islands, scientists aboard the three-man submarine Alvin made a startling discovery. Though they were cruising at a depth of more than 1 1/2 miles, where the absence of sunlight usually results in a barren sea bottom, they found a veritable oasis of life. Clustered around deep-ocean vents, they spotted giant clams, pale yellow mussels, white crabs and worms nearly 5 ft. long.

Since then, scientific astonishment over the discovery has burgeoned. Unlike most terrestrial life, these creatures in the deep survive without the benefit of sunlight to supply energy or help create food supplies. Rather, they rely totally on the earth's internal heat. Explains Marine Microbiologist Holger Jannasch of the Woods Hole (Mass.) Oceanographic Institution, which operates the Alvin: "If the sun didn't shine any more, these deep-sea populations would still be growing, while we and all the green plants would die. They depend only on Mother Earth."

Scientists have been hoping to learn more about how Mother Earth sustains these strange communities. Now they are getting their chance. Under a $1.7 million grant from the National Science Foundation, the Alvin, on loan from the Navy, is making a new series of exploratory dives. The expedition is called "Oasis," and its target area is a region of undersea volcanic vents nearly 150 miles south of Baja California. The site is part of a seismically active region where lava oozes from fractures in the earth's crust.

Descending to depths of 8,500 ft., the Alvin has found not only more creatures of the Galapagos variety, such as giant worms, but other oddities: several species of snails, worms, clams and a jellyfish. Some are so novel that they defy the taxonomic abilities of the biologists aboard the expedition's mother ship, Melville, operated by the Scripps Institution of Oceanography. Among these unknown wonders: white eellike fish that hover around the scorching vents. For lack of a better name, the scientists have labeled them "21-degree-north vent fish" (after the latitude of the site). Researchers believe the vent fish may be the first vertebrate discovered whose existence does not ultimately depend upon sunlight.

Intensive study of the creatures has provided some tantalizing hints about the bizarre life processes in this lightless world. On the earth's surface, all life, with minor exceptions, stems from the sun. Green plants, synthesizing sugars and other carbohydrates out of water and carbon dioxide in a sunlight-powered process called photosynthesis, provide sustenance for virtually all other living things. But in the world of the deep sea vents, there is no sun. How then do its inhabitants survive?

The answer lies in the vents. As sea water circulates within the earth's cracks, it heats to more than 700DEG F, absorbs minerals from surrounding rocks and becomes saturated with sulfur-rich compounds. Under heat and pressure, these compounds are converted to hydrogen sulfide. A poisonous, malodorous substance, it is a feast to bacteria living in the geysers. They thrive upon it and, in turn, become the primary food source in this ecological niche. The worms, for example, harbor bacteria by the billions within their long bodies. The bacteria supply the worms with sustenance while the worms' remarkable blood brings sulfides to the bacteria, along with oxygen and carbon dioxide from the sea water. When the sulfides combine with oxygen and carbon dioxide, they release energy. Thus the chemical energy bound up in the hydrogen sulfide plays the same role the sun does on the earth's surface.

Life at the vents takes extraordinary turns. The crabs scurry from cold water into the scorching vents and snatch bits of food without harming themselves. Unlike their slow-growing, shallow-water kin, the giant clams quickly swell to a length of a foot. One reason for the rapid development may be the short life of the vents. Typically, they last only a decade or so. Unless the organisms can mature quickly and scatter their larvae before the heat gives out, the species will die. Most puzzling of all is the ability of the creatures to survive with so much hydrogen sulfide in their systems. Says Scripps Zoologist Robert Hessler: "Nobody understands how the animals are taking care of this poison."

The answers to these questions may do more than merely satisfy scientific curiosity. As biologists learn the secrets of deep-depth survival, the knowledge may lead to more constructive use of materials like hydrogen sulfide. Says Jannasch: "We may be able to grow bacteria from it, feed this biomass to, say, clams and form the base of an aquaculture."

In fact, Woods Hole is already testing the idea in some experimental mussel tanks. Which suggests that the deep-sea creatures may yet have a thing or two to teach us about living on earth. --By Frederic Golden. Reported by Joseph Pilcher/ Mazatlan

With reporting by Joseph Pilcher

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