Bay Journal

Chesapeake Bay night-lights add sparkle to woods, water

  • By Kathy Reshetiloff on July 01, 2001
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Every August, as the Earth enters a region of space containing high concentrations of solar debris, nighttime sky watchers are rewarded with a wonderful light display known as the Perseid meteor shower.

But you don’t have to be an amateur astronomer to see magnificent light shows. Some animals produce light from within their bodies. This phenomenon, bioluminescence, gives these creatures a visual aura.

Phosphorus was thought to be the source of light in living creatures. Researchers now know that bioluminescence is accomplished through oxidation (the addition of oxygen) in an animal protein called luciferin. When a molecule of oxygen, either in a gaseous form or mixed in a liquid, and an enzyme known as luciferase combine with luciferin, the resulting new molecule is excited and gives off light. Unlike fuel combustion, there is no heat associated with luminescence.

Many bioluminescent animals can create this light only at night. Even when these creatures are subjected to darkness during the day they either will not glow or will glow just barely. Because of this, it’s believed that bioluminescence may depend upon an animal’s daily cycle or the amount of time that animal is subjected to dark conditions.

The most familiar light producer is the firefly or lightning bug. During June and July, after spending most of the year underground, fireflies emerge to attract a mate. Light, produced in the firefly’s abdomen, flashes on and off in a specific pattern. There are more than 2,000 species of fireflies and each has its own code.

In most firefly species, the males fly about while flashing their code. Females, usually on the ground, will flash the same code back. The male then joins the female on the ground, where they mate.

This type of communication is not without danger. Some female fireflies are excellent mimics, and can flash back the signal of another species. The enamored male, believing he has found his mate, flies down, only to be devoured by the impostor.

The aquatic world supports the greatest number of bioluminescent animals. The Chesapeake Bay, especially Virginia waters, supports its share of “living lights.”

Many microscopic bacteria and plankton possess the ability to produce light. Noctiluca, about 1/16 of an inch in size, belongs to a group of plankton known as dinoflagellates. Its name literally means “night light.”

Noctiluca, like many bioluminescent life forms, lights up in response to physical disturbances in the water. While the light from one Noctiluca is tiny and brief, many individuals gathered together create an eerie greenish glow in the water.

Another dinoflagellate, Ceratium, has a three-pointed, anchor-shaped body that produces a twinkling light.

Larger light creatures include the moon jellyfish and species of comb jellies.

The moon jelly sports four pink, horseshoe-shaped gonads atop its 10-12 inch “head.” Its tentacles are marginal and very short. The light from a moon jelly appears bluish.

Comb jellies are similar to other jellyfish in their translucent, gelatinous appearance, minus the stinging tentacles. Instead, eight rows of fringed plates, called combs, propel them through the water.

One comb jelly common in the Bay is the sea walnut, named for its oval shape. When disturbed, the sea walnut flashes a green light along its combs. Although only 4 inches in size, the effect created by hundreds of sea walnuts congregating together is quite startling.

Only a small part of the aquatic life in bays and shallow zones of the oceans and bays are bioluminescent. In deep ocean zones, up to 80 percent of all jellyfish, squid, shrimp and fish are luminescent. In the pitch blackness of these ocean depths, it seems logical that so many animals can produce their own light.

In shallower water areas like the Chesapeake Bay, bioluminescence is a response to an outside stimulus. Touch, wind, rain or extremely choppy water may cause a creature to light.

Researchers also believe that bioluminescence serves a variety of other purposes. The light may protect the animal by startling or confusing a potential predator or by disguising the prey’s true size and form.

Flashes and patterns of light may be a form of communication for attracting a mate, as with the firefly, or as a warning to others of its kind.

Bioluminescence in nature is everywhere from backyards to the Chesapeake Bay. So if you miss the Perseid shower and still crave a light show, take a walk near a dark field and watch the firefly display. Lie on a dock after a rain and peer into the murky water. If you are lucky, these usually dark waters will provide a glimpse of fantastic creatures dancing in their own light.

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About Kathy Reshetiloff

Kathryn Reshetiloff is with the U.S. Fish and Wildlife Service’s Chesapeake Bay Field Office in Annapolis.

Read more articles by Kathy Reshetiloff

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