An astonishing variety of living things generate light: bacteria, beetles, flies, fish, krill, millipedes, comb jellies, worms, squid, shrimp. For reasons we don’t fully understand, most of these creatures live in the ocean. Below 3,000 feet, where sunbeams never reach, more than 80 percent of swimmers and floaters flash or glow in some manner. All fish that make their homes in these rayless ocean zones have eyes, presumably for the sole purpose of viewing such displays, some of which appear as ghostly blue-green beacons, others of which flash like Christmas strands that festoon rippling, pulsating forms of alien life.
However they display it, on land or in the sea, all bioluminescent species use their light strategically. In their recently published primer, Bioluminescence, J. Woodland Hastings and Thérèse Wilson write that fireflies blink to attract a mate. Anglerfish dangle a pouch of glowing bacteria above their mouths to lure prey. Blind millipedes shine to remind predators that they’re poisonous. Some fish, shrimp, and squid illuminate their bellies to match the intensity of whatever moonlight or sunlight is filtering down from above, effectively camouflaging themselves from any creatures swimming below.
Upon encountering the spectacle of oceans shimmering with bioluminescent plankton, René Descartes, the seventeenth-century French philosopher, thought he was witnessing combustion, and posited that sea-salt crystals were flammable. In fact, bioluminescence is created not by heat but by a chemical reaction. When a compound called a luciferin reacts with oxygen and is then catalyzed by an enzyme called luciferase, the resulting energy appears as light. But scientists don’t believe bioluminescence evolved for the purpose of illumination. Instead, it likely arose soon after oxygen did—some 2.5 billion years ago—as a way of helping early organisms prevent this increasingly ubiquitous (and toxic-in-high-doses) element from damaging their cells. Bioluminescence converts oxygen into light energy hyperefficiently; indeed, says Michael Latz, a marine biologist at the Scripps Institution of Oceanography, “it is actually the most potent antioxidant that we know about.”
The more researchers learn about what triggers bioluminescence, the more they can use it as a tool to study systems previously invisible to us. Scientists have already genetically engineered harmless bioluminescence into plants and animals, including the cultured cells of humans, in an attempt to observe the regulation of certain genes and the activity of proteins. Because dinoflagellates—plankton that are the most common source of bioluminescence at the ocean’s surface—glow with a brightness directly proportional to their level of agitation, researchers have been able to use them to illuminate the complex forces at work inside a single wave, as well as to highlight the fluid dynamics that allow dolphins to shoot through the water with such remarkable speed.
Bioluminescence also offers new ways to observe the health of ecosystems. In the Caribbean, Latz is studying bays that glow year-round, thanks to an abundance of dinoflagellates. “The bioluminescence is a sentinel—we can use it as an indicator of environmental quality,” he says. Storms can disturb a bay’s dinoflagellates and cause its glow to dim until things settle back down. By tracking shifts in brightness, Latz’s team can measure the bays’ resilience in an era when climate change is increasing the frequency and intensity of coastal storms. The marine biologist Edith Widder, of the Ocean Research and Conservation Association, has used bioluminescent bacteria to map the distribution of heavy metals and fertilizers in the Indian River Lagoon, one of Florida’s most troubled waterways.
More than ever, it seems, scientists are able to see new evidence of ecological upsets like man-made climate change and hazardous waste in the form of glaring, real-time warnings. But are we willing to dim some of our own lights in deference to the natural lamps we’re beginning to turn to for these environmental alerts?
Now that humans have illuminated so much of the world, the darkness that makes bioluminescent signals so visible—and so valuable to the species that generate them—is disappearing. Indeed, says Latz, artificial nighttime glare is already interfering with the observability of the bays he studies, threatening to overpower the radiance that broadcasts how they are faring. “I consider them ecological wonders that need to be preserved,” he says. He’s hoping for a brighter future—of deeper darkness and more easily visible bioluminescence. “The darker it is, the better you can see it.”
Illustration by Jesse Lefkowtiz
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