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BY SCOTT KIRKWOOD
In the cool, deep waters off Glacier Bay National Park in Alaska, a warm blue light emanates from just beneath the surface, prompting doubletakes from those aboard boats and those watching from the shore. It's not the apparition of a sailor whose grave lies at the bottom of the ocean; it's the slightly eerie glow of ocean creatures capable of bioluminescence - simply put, light produced by living organisms.
Most of us have encountered bioluminescence in the summer months courtesy of the business end of a firefly, but not as many realize that under-water creatures are capable of the same fireworks. Visitors to Virgin Islands National Park, California's Channel Islands, and Florida's Biscayne Bay all have the opportunity to see the dazzling light show for themselves. Although scientists haven't nailed down all the reasons creatures exhibit bioluminescence, they can make some pretty good guesses based on the conditions that flick the switch.
"What typically sets them off is turbulence: If you disturb the water, they'll flash," says Lewis Sharman, ecologist at Glacier Bay National Park and Preserve. "The presumption is that bioluminescence has some sort of adaptive value. The process requires some energy, and plants and animals typically don't use energy for nothing-there's usually a reason for it."
Some species seem to be communicating with one another, whereas others use the ability to attract prey or to avoid becoming prey.
According to Sharman, just about every group of marine animals contains at least one species that can bioluminesce, with countless clever applications. One study shed light on the unique way that bioluminescence helps phytoplankton avoid being consumed by copepods (small crustaceans that some liken to "insects of the sea"). When copepods encountered swarms of phytoplankton - generally a prime grazing opportunity - the phytoplankton's ability to light up acts as a sort of motion-detecting floodlight, exposing the predator and attracting creatures that feed on copepods, thus conferring an adaptive advantage to phytoplankton with the capability.
Among the larger fish, the value of bioluminescence is often more straightforward. One popular subject of school filmstrips from years past and cable documentaries of today is a deep-sea creature called the anglerfish, whose lighted lure attracts inquisitive smaller fish, which soon become dinner. Still other animals can produce red beams of light-because most sea creatures can see only blue colors, the light illuminates prey or potential mates without alerting creatures in the vicinity, like a pair of night-vision goggles for the underwater set.
Although scientists aren't sure of the reason behind every animal's ability to bioluminesce, they're pretty clear on the chemical reaction that brings it about. Luminescence, in general, is defined as any emission of light not caused by heat, such as television, neon lights, and fluorescent lights (as opposed to incandescent lights found in most homes, which produce light as a byproduct of heat). One simple example of luminescence is the glow sticks children often carry on Halloween: Two separate chambers are filled with fairly benign chemicals - when the glow stick is snapped in the middle, the chemicals are allowed to combine, and the ensuing reaction generates light. Fireflies, anglerfish, and other creatures create light by releasing the chemical luciferin, which combines with the enzyme luciferase to create light.
It's probably no surprise that the deeper you travel below the surface of the water, the more bioluminescent creatures you're likely to encounter, because the ability becomes more valuable as surface light becomes more rare. But park visitors don't need to don SCUBA gear to see this phenomenon in action. Microorganisms that get caught in a boat's wake create a glowing trail, the paddle of an oar is often enough to stir up a colorful light beneath the surface, and the crashing of waves on the shore will produce fireworks for those walking along the beach late at night. So the next time you witness any of these scenes at a coastal park, you'll know the light comes from one creature communicating with another, like a message in a bottle washed up on the shore. |
