Living Lights

What would it be like to glow in the dark?

1 Very few organisms that live on land have the ability to glow in the dark, but it is a surprisingly common characteristic among deep-sea marine creatures. In fact, about 90 percent of animals that live 200 to 1,000 meters below the surface of the ocean are bioluminescent.

2 The word bioluminescence (bahy-oh-loo-muh-nes-uhns) comes from the Greek word bios, which means living, and the Latin word lumen, which means light. It refers to organisms that produce light as a result of a chemical reaction. Bioluminescence is a cool light. In a lightbulb, about 97 percent of the energy is used to create heat, and only 3 percent is used to create light. When bioluminescence is produced, very little energy is used to create heat. This is one reason that scientists are so interested in learning about bioluminescence and how it might be used to create more efficient, less wasteful light sources.

3 Ocean animals use bioluminescence in various ways. You might think that light would not be very effective as camouflage because it would draw attention to an animal instead of helping it hide. However, if you were a predator hunting a bobtail squid and you looked up at the squid’s belly, its bioluminescence would allow it to blend with the stars of the night sky.

4 Other animals use bioluminescence to attract mates. This is the case with fireflies on land, who use light signals to attract others of the same species. It is also true of ocean animals like the Bermuda fireworm.

5 One species of squid uses bioluminescence to confuse predators. If it feels threatened, it spews a cloud of bioluminescent chemicals. While the predator is surprised and confused, the squid has time to quickly escape. 6 Another possible use of bioluminescence is to lure prey. The cookie cutter shark is one animal that uses its light in this way. Patterns of bioluminescence on the shark’s underside may resemble small fish to predators like tuna or mackerel. When they come closer to investigate, the shark attacks. The anglerfish uses a similar method to capture prey. It extends a glowing lure from an appendage on its head. Other fish mistake the glowing lure for a meal and venture closer. When they do, the anglerfish moves quickly and snaps them up.

7 Because many bioluminescent animals live deep underwater, most people don’t have the opportunity to observe them. However, tiny one-celled creatures called dinoflagellates (din-uh-flaj-uh-leyt) live in the sea and produce much of the visible bioluminescence near the ocean’s surface. In areas that have large numbers of dinoflagellates, the motion of waves, a boat, a porpoise, or even a hand can easily disturb them and cause them to glow. On a dark night, this eerie but beautiful sight can create quite a light show in the ocean!

Spectrum Reading Grade 6

90

1. Write a sentence that tells the main idea of the passage.

2. Explain one way in which an animal can use bioluminescence to lure prey.

3. What kind of creature produces much of the visible bioluminescence near the ocean’s surface?

4. How does bioluminescence help camouflage the bobtail squid?

5. How is bioluminescence different from the light produced by a lightbulb?

6. What can cause dinoflagellates to glow?

7. Check the line beside the word or words that best describe what type of selection this is.

science fiction _____ informative _____ fantasy

8. The Latin root mar means sea. Find a word in paragraph 1 with the root mar.

9. The Latin root fic means make or do. Find a word in paragraph 2 with the root fic.

10. The Latin root tract means pull or drag. Find a word in paragraph 4 with the root tract.

Spectrum Reading Grade 6

91