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Images: Marine Life Adaptations to Light

The dark backs and light undersides of these near-surface fish help them match their environment in the open ocean. To a predator looking from above, their dark backs seem to blend into the dark depths. From the side, their lighter sides blend with the sunlit water. (Photo by Larry Madin, Woods Hole Oceanographic Institution)

Many open ocean animals use invisibility to hide in plain view. Adapted to limitless, featureless blue surroundings, this planktonic ctenophore, Cestum, lives near the ocean surface. The complete transparency of its body makes it almost impossible to see against the open ocean waters. (Photo by Larry Madin, Woods Hole Oceanographic Institution)

The hatchet fish is well prepared for the midwater ocean's light levels. Bright silver sides reflect whatever light surrounds it. Long, tubular eyes capture and detect low light levels. Living at depths from 200 to 1000 meters, it has ventral (underside) light organs that can produce bioluminescence to match light coming from above, making it less visible from below. (Photo by Larry Madin, Woods Hole Oceanographic Institution)

With enormous upward-looking eyes that fill half its otherwise transparent body, the deep-living shrimplike amphipod Cystisoma is well-suited to its dim world. It needs such large eyes to detect the little light available in its midwater environment (800 meters), and red eyes, at that depth, look black—and invisible. (Photo by Larry Madin, Woods Hole Oceanographic Institution)

Atolla is a jellyfish common from midwater, about 500 meters deep—where there is still a small amount of sunlight, to bathyal depths of 4500 meters—far below the limit of sunlight's penetration. Where there is light, its red color looks black, making it hard to see. It also produces brilliant bioluminescence, possibly to frighten predators. (Photo by Larry Madin, Woods Hole Oceanographic Institution)