Explore the Deep Sea

Life in the Deep

Hot oases in chill darkness

Snails photographed in the Lau Basin. Image courtesy of D. Desbruyeres

Before the first dives to mid-ocean ridges in the late 1970s, researchers expected to encounter a barren, mostly lifeless landscape. Algae and plants cannot survive without sunlight, which does not penetrate ocean water below about 1000 meters. Without plants or algae to form the base of the food chain, how could there be much to eat apart from a sparse sprinkling of "marine snow"—the corpses of animals and plants which died nearer the surface? But patches around active volcanoes and vents teem with life.

Living without sunlight

Tubeworms rely entirely on symbiotic microbes for food. Photo courtesy of K Van Damm

Some animals found around vents get their food by eating other organisms. But many of the animals living near deep-sea vents obtain their food in a very different way: they play host to particular species of microbe that live inside their bodies and manufacture food by combining certain chemicals found in vent fluids with oxygen found in seawater. The microbes give some of the food they manufacture to their animal hosts.

Hostile conditions

A hydrothermal vent. Photo courtesy C. Fisher

Organisms living near deep-sea vents have to be able to tolerate or avoid the extreme conditions there. The pressure is immense—hundreds of times greater than that at the ocean surface. The ocean water is just a few degrees above freezing, but fluids jetting out of seafloor vents can be tens or hundreds of degrees hotter. Many of the chemicals in the vent fluid are extremely toxic, even at low concentrations.

New species galore

Deep-sea barnacles. Photo courtesy C. Fisher

Mussels, shrimp, crabs, snails, fish, huge worms and many other lifeforms have been discovered since the first dives to vents on the ocean floor. Most of these organisms were new to science, and to this day many new species are discovered each year.

Where (and when) you are determines what creatures you find

Different oceans contain different species. For example, deep-sea vent sites in the Atlantic contain many shrimps and mussels, whereas sites in the East Pacific have abundant tubeworms and clams as well as mussels. The depth and composition of the water also affects which species we see, as does the age of the site. Volcanic areas are often extremely dynamic. Vents can form suddenly when the crustal rocks crack, and die some time later (e.g. as the crack gets plugged with rock). Some vents are long-lived and others are short-lived. Some vents blow extremely hot fluid, while others merely seep warm fluid. The chemistry of the fluid exiting the vent varies—some vents contain more toxic chemicals than others. This variation in space and time creates a rich variety of habitats for vent creatures.

Life away from vents

Away from vents, the deep ocean is far from barren, and certain patches are especially rich in life. For example, whale carcasses support a wide range of organisms, including some that are closely related to vent species. Deep-water corals also function as essential habitats for a wide range of other creatures; they are found at depths down to about 2000m.

Next: Microbes