Where Do the Animals at the Bottom of the Ocean Get Their Food?

The Food Web of the Upper Ocean

• Most life in the ocean is part of the familiar food pyramid, with photosynthesizing plants and algae at the base. Although these photosynthesizers can only live near the surface, even the zooplankton that feed upon them live deeper, taking refuge from vision-dependent predators during the daylight hours. An enormous variety of organisms make up this food web, from tiny dinoflagellates through copepods and krill to sharks and whales. As well, a significant amount of organic material enters the oceans from land ecosystems, which are also based ultimately upon energy from the sun.

Tablescraps on the Ocean Floor

• When a shark tears into a seal, not all of the seal ends up inside the shark. Many of the scraps will be snapped up by smaller fish, but some will eventually settle onto the ocean floor. So will those bits that DO get into the shark, when the shark finishes digesting them. A a constant gentle rain of organic material falls through the depths, providing food for bottom-dwelling scavengers and microbes. The 200- ton carcass of a whale can support a teeming undersea community for decades.

Deep Sea Vents

• In volcanically-active places on the ocean floor, superheated seawater spews from geysers, rich in dissolved minerals and other volcanic products, notably hydrogen sulfide. Hydrogen sulfide is chemically energetic, and microbes called archaea are able to extract this energy for their own cellular processes. These microbes, sometimes called extremophiles because of their ability to survive in extremes of temperature and acidity, form vast colonies around these deep sea vents and serve as the basis of a separate food web, supporting exotic crabs, sponges, worms, mollusks and other strange creatures.

Other Chemistries

• Anywhere chemical energy is found, chances are some kind of bacteria or archaea has found a way to get at it. Scientists have found bacteria that derive their energy from oxidizing the iron and other metals in the hulls of sunken ships. Other bacteria feed upon deposits of solid methane hydrates on the sea floor. There may even be archaea living throughout the planet's crust, under the continents as well as the sea, drawing their nourishment from the chemistry of the rocks themselves.