Every summer, as the Earth enters a region of space containing high concentrations of solar debris, nighttime sky watchers are rewarded with a wonderful light display-the Perseid meteor shower. This year, meteors will radiate out from the constellation Perseus from late in the evening of Aug. 11 to the morning of Aug. 12.
But one doesn'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 adding of oxygen) to a protein in the animal known as 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.
The most familiar of the light producers 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 section, flashes on and off in a specific pattern or code. There are more than 2,000 species of fireflies and each species has its own light 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, flashing back the signal of another species. The enamored male-believing he has found his mate-flies down, only to be devoured by the imposter.
The aquatic world supports the greatest amount of bioluminescent animals. The Chesapeake Bay, especially in its southern waters, supports its share of living lights. Many microscopic bacteria and plankton can produce light. Noctiluca, about 0.0625 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.
The light from one Noctiluca is tiny and brief. Many individuals gathered together, though, create an eerie greenish glow in the water. Another dinoflagellate, Ceratium, has a three-pointed, anchor-shaped body that produces a twinkling light effect.
Other larger light creatures include the moon jellyfish and some 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 deeper ocean waters, 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 up. 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.
Natural light shows are everywhere, from backyards to the Chesapeake Bay. So if you miss the Perseid shower, 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, the usually dark waters will provide a glimpse of fantastic creatures dancing in their own light.