Jellies Down Deep
How the Jelly Got Its Glow
The deep sea is ruled by darkness. Sunlight does not penetrate much beyond 60 meters (about 200 feet) below the ocean’s surface. To see the animal life, gelatinous or otherwise, that thrives at greater depths, a submersible vehicle like the ones used by scientists in Monterey Bay comes equipped with powerful lights. To truly understand the life down there, however, those lights must be turned off. That’s when the native lights become visible—the ghostly blue flickers of bioluminescence produced by virtually every organism of the deep.
“There’s a whole netherworld of the deep sea that we don’t see when we have our lights on,” says Kevin Raskoff, a scientist at California State University, Monterey Bay. “And that’s the natural light of the deep sea: bioluminescence.”
“It’s such a bizarre and exciting phenomenon to see,” agrees Steven Haddock of the Monterey Bay Aquarium Research Institute. “The first time you see one of these animals just glow, it’s pretty amazing.”
Bioluminescence is light produced by a chemical process within a living organism. The glow occurs when a substance called luciferin reacts with oxygen. This releases energy, and light is emitted. An enzyme called luciferase facilitates the reaction. Sometimes luciferin and luciferase are bound together with oxygen into a single molecule, or photoprotein. When an ion such as calcium is present, an ensuing reaction emits light. To glow on a regular basis, an organism must continually bring fresh luciferin into its system. Some acquire it through their diet; others produce their own.
Bioluminescence is relatively rare on land. It is most commonly seen among certain insect species like fireflies and glowworms (a form of insect larvae); some mushrooms and fungi also glow in the dark. In the deep sea, however, bioluminescence is found in virtually every type of animal: squids, octopuses, fishes, shrimps, single-celled organisms, and jellies of all kinds. Two thousand years ago, the Roman scholar Pliny the Elder noted that if he rubbed the slime of Pulmo marinus, a jellyfish from the Bay of Naples, on his walking stick, it “will light the way like a torch.” Raskoff estimates that 90 percent of all the animals in the deep sea are in fact bioluminescent. “In the deep sea, it’s the norm. You’re odd man out if you don’t bioluminesce.”
Underwater, bioluminescence finds all manner of purpose. Some animals use it to attract mates. A male sea-firefly (Vargula hilgendorfii) will squirt out a bright dot of light, zip upward, and then squirt another and another, essentially drawing an arrow that points out his whereabouts. Other creatures use bioluminescence to detect or lure prey. The viperfish ( Chauliodus sloani) dangles a luminescent lure in front of its mouth and then snaps up any creature that dares to investigate.
