Who glows there?
In the ocean, the light quickly fades as you descend. Sun-
shine warms the surface, bathing it in sparkling light. Fish
with silvery scales, such as herring and sardines, blend in with
the glittery sea. In the deep-blue “twilight zone,” between 200 and
1,000 meters, the sunlight is a barely detectable glow. The sun’s rays
fail to reach the inky abyss beyond a depth of 1,000 meters.
Marine animals swimming in the vast, open ocean have no place to hide. Danger lurks in every direction. Many
fish find food in the water above by searching for a dark shadow in the sun’s light. But their prey have clever ways to dis-
guise their profiles and dodge the predators. For example, the light produced by the midshipman fish helps it to hide, instead
of being seen. A gentle glow radiates from its belly and blends in with a hint of moonlight, masking the shadow and silhou-
ette of the fish.
In the deep ocean, the cookiecutter shark keeps a low profile thanks to light-emitting organs in its lower body, called
photophores. When the fierce shark is viewed from below, it blends in with the light above it. The photophores on its
underside disguise its outline. Except for a dark band around its throat, light on this ferocious beast breaks up its
cigar-shaped silhouette. From below, the band makes this shark look like a small fish—an attractive meal for a large
predator. When a bigger predator comes near, the cookiecutter shark grabs hold of the predator’s body with its lips
and bites, using its small, sharp teeth to remove a thick biscuit-sized chunk of flesh, which it
swallows before releasing its grip.
Many red and black fish live at depths between 600 and 1,000
meters. Sunlight, which contains every color of the rainbow,
As this red fish travels deeper, it appears less and less
red because light of different colors is slowly filtered out
as the depth increases. Red light, which has a relatively
long wavelength and less energy than light with other
THE DEEP SEA IS A PLACE OF BONE-CHILLING WATER, NEAR- total darkness, and lung-collapsing pressure. Life in these xtreme conditions seems impossible. Surprisingly, not only is there life in the deep sea, there is also light—in every color of the rainbow. Many marine organisms emit light, and they do it in incredible ways. Some simply flash or flicker, while others fire “light bombs”
or emit sparkles that glimmer. One organism produces a glowing display
that is so dazzling it appears to spin like a roulette wheel of light.
To study how deep-sea creatures emit light, scientists launch submersibles and remotely controlled vehicles, both manned and unmanned. They
use fiber-optic cables, mechanical arms, and lowlight cameras and video
to find new species of sea animals, such as supergiant shrimp, big-eared
“Dumbo” octopi, and hairy-legged “Yeti” crabs.
Marine animals in the deep sea are masters of light. They use it in
ways we could never imagine. Research on these animals has led to
novel methods of tracking disease, illuminating cancer cells, and detecting water pollution. In the future, it may improve satellite sensors and
even how we detect cancer.
By Linda Zajac