The setting sun fortells an incredible transformation occurring beneath the ocean surface. As darkness descends, the water becomes alive with displays of bioluminescence -- living light produced by a myriad of organisms -- that has a major impact on virtually all biological communities. If you study bioluminescence as I do, your day is just beginning. In the ocean, bioluminescent organisms are everywhere, inhabiting all depths covering all the world's oceans. Remember the spectacular red tide last year? A giant bloom of phytoplankton -- plant-like microscopic organisms -- discolored the water brown due to their immense numbers, as many as 2 million cells per liter. To me the most memorable feature occurred not during the day but at night. These cells produced bioluminescence that highlighted breaking waves with streaks of electric blue light, and traced the paths of swimming fish. The red tide phytoplankton use their flashes as a burglar alarm so they won't get eaten; in this case, the "burglar" is the animal trying to eat them. In doing so, it stimulates the cells to make flashes of light, attracting still other predators which try to eat the burglar. So if you're not careful around these luminescent plankton, you'll end up in someone's stomach! It's enough to make you lose your appetite, which is exactly its purpose. Even those animals not interested in eating dinoflagellates must be wary of their movements, because the ocean is like a luminescent minefield. Any inadvertent motion may set off an "explosion" of plankton luminescence which exposes the unlucky animal to hungry predators. In the perpetual darkness of the deep sea, where sunlight never reaches, bioluminescence also serves other purposes. Angler fish grow luminescent bacteria in a special structure which dangles at the end of a stalk projecting from their forehead. Just as fisherman use a glowing lure for night fishing, in the perpetual darkness of the deep sea these fish attract prey by their glowing lures. Still other fish produce far-red beams of light from areas on their cheeks. Because most deep-sea animals can only see blue colors, the red luminescence serves as an invisible searchlight for finding prey or mates. Jellyfish so delicate that they disintegrate when touched emit brilliant displays of light when disturbed. Their message is leave me alone. Whatever its purpose, bioluminescence is produced as a result of a chemical reaction which releases lots of energy. Unlike a light bulb, in which electrical energy is converted into light, with some energy lost as heat, the bioluminescent reaction is 100% efficient in channeling all the energy into light. Bioluminescence serves man as well. The jellyfish biochemical system is used to measure calcium levels, while that of the firefly measures ATP, the primary energy source of all cells. The genes for the bacterial, firefly, and jellyfish luminescent proteins can be spliced into the genes of other organisms to monitor gene activity. When that gene is turned on, the cell glows! Trace amounts of chemicals and pollutants are detected using a bioluminescence test. Interested in seeing bioluminescence in the San Diego area? Don't bother looking for fireflies, which fly around on balmy summer evenings using their light flashes to attract mates; they don't live here. Instead, view the flashlight fish at the Scripps Aquarium. These fish harbor luminescent bacteria in special organs in their cheeks. They shutter the light to make a Morse code of flashing for signaling their friends and attracting prey. More adventurous? Kayak in San Diego Bay and experience the glowing mating dance of thousands of swimming worms when the moon is right. Find a dark beach and check out the plankton bioluminescence stimulated by the breaking waves. Or go for that midnight swim and watch the sparkles of living light as you move through the water. And remember that bioluminescence is a natural part of how organisms interact with their environment and each other.
Bioluminescence / biolum@ucsd.edu,