84 Luminescence in Nature-Low

Luminescence in Nature FOCUS Question Why does bioluminescence occur in nature?

LIVING LIGHT Imagine entering a dark forest and seeing a faint light. The forest floor shines green while floating yellow lights blink. Up ahead, a soft glow from the mouth of a cave beckons. Have you wandered into an enchanted land? Not quite. The lights you see are not magic at work—they're science. Some living things can produce light through a chemical process known as bioluminescence (by-oh-loo-muh-NEH-suhnss). During this process, a chemical called a catalyst helps oxygen combine with another chemical called a substrate. When oxygen and the substrate combine, light is produced. The organism glows!

Most bioluminescent light is blue or green. Some living things produce other colors, though. The railroad worm can actually glow two colors. Its head shines red, while its body glows yellowish- green. Unlike some lightbulbs that get hot when making light, living things don't get hot when they're shining. That's because bioluminescent light produces very little heat. Some living things, as well as nonliving things such as rocks and minerals, can glow in a way that is different from bioluminescence. These things do not make light. but instead can give off fluorescent light They absorb light from another source and then release it as a different color. Still other things may have phosphorescent light, which is similar but can glow for a longer time.

WHY LIGHT UP? What is the purpose of an organism's ability to make light? Some organisms glow to attract food. Cave glowworms bright glow attracts insects that then get stuck in the worms sticky mucus threads. Some organisms glow to communicate. Adult fireflies produce flash patterns to identify themselves as either male or female. At the larval stage, though, they glow as a means of defense. Firefly larvae taste terrible to predators. They light up to warn predators that those that strike will end up with a mouthful of yuck! Some organisms glow to reproduce. Glowing mushrooms attract beetles and wasps that then distribute their spores on the ground, where they sprout and grow into new mushrooms.

SHINING SEAS Bioluminescence is actually much more common in the ocean than on land. Sunlight does not penetrate the depths of the ocean. In the darkness, flashes of bioluminescent light really stand out. Most luminescent marine creatures do not use the light to see in the dark, though. Some animals use it to confuse attackers. For example, some squid produce flashes of light to startle predators. This gives the squid a chance to sneak away quickly. A type of organism called a brittle star actually detaches one of its arms. Predators pursue the glowing arm while the rest of the brittle star goes dark and crawls away. Wowser! More than 75 percent of deep-sea creatures produce their own light.

Sea cucumbers take this idea a step further. Some can detach a glowing part of their body and attach it to a nearby fish! The fish swims off with the glowing body part while the predator gives chase. Meanwhile, the sea cucumber dims the rest of itself and crawls or swims away. Some sea animals use bioluminescence as a kind of two-tier defense system. Tiny creatures called dinoflagellates (dy-noh-FLA-juh-luhts) float on the water's surface. Swarms of them flash at night to startle fish that feed on them. The flashes also signal to larger animals that fish are in the area. The larger predators come along to eat the fish feeding on dinoflagellates!