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FEATURE ARTICLE

An Empire Lacking Food

Once viewed as a barren expanse, the deep seafloor is a biologically elaborate ecosystem whose fate is tied to life above, near the sea surface

Craig McClain

2010-11McClainF1.jpgClick to Enlarge ImageLet me reintroduce you to planet Earth. Nearly 64 percent of its surface, close to 208,640,000 square kilometers, sits below 200 meters of water. The lack of light at those depths prohibits photosynthesis, the biological energy conversion system that is the foundation of most food webs. Thus our world, with its abundant deep oceans, is dominated by food-poor habitats. The consequences of this reverberate throughout the deep sea—but not in the ways long assumed.

Two centuries ago scientists believed the lack of photosynthesis, and therefore of plants, precluded the existence of animal life in the deep sea. To those early scientists, the deepest depths represented a vast wasteland littered with shipwrecks and skeletons. But what actually exists on the deep seafloor, now visible thanks to decades of exploration and advances in technology, is more complex than anyone anticipated. And it all starts with organisms dwelling not on the ocean floor but near its surface.

2010-11McClainF2.jpgClick to Enlarge ImageEach year approximately 16 gigatons of carbon fixed by phytoplankton are thought to sink to the ocean interior. This amount is a mere 3 percent of the total produced at the ocean surface. Consider that 3 percent of a five-pound bag of sugar is less that five-and-a-half tablespoons. This small amount of fluxed carbon, carried largely by “marine snow,” dusts the seafloor and represents the only food source for the majority of organisms in the deep. Yet enough carbon arrives to drive every aspect of life in this remote habitat. Conundrums abound in this place where so little food is available. Profound biodiversity exists in the deep sea. Unexpected evolutionary size adaptations and other anatomical novelties are common there—evidence of life’s ability to adapt to environmental extremes.




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