National Geographic : 1971 Jul
yet seem to produce light." Others noted with awe how the sea would glow during certain seasons, or flash when disturbed by an oar or by winds. They of course could not have known that "sea fire" is produced by minute living organisms. For centuries men ascribed magical or sacred powers to tree trunks that shone at night without being consumed, unaware that the cold "fire" came from bacteria or fungi growing within the rotting wood. Scientists have identified several dozen luminous spe cies among the fungi (pages 60-61). Smallest among luminous organisms are certain species of bacteria about 1/20,000th of an inch in diameter. Growth of such bac teria sometimes causes a rotting fish, a piece of old meat, or a dead caterpillar to glow. Tales of glowing corpses on a battlefield could only be based on the presence of lumi nous bacteria growing on the decaying skin. Certain noninjurious bacteria, cultured in special organs, light up some squids and fish. Others produce their own light. Among in vertebrates, luminescent marine creatures also include shrimp, jellyfish, sea pens, comb jellies, worms, mollusks, tunicates, hydroids, protozoans, and dinoflagellates. The last, in particular, can be spectacular. Paired belly lights beam from Argyropelecus, which dwells in quarter-mile depths of the Mediterranean. Among the vertebrates, only fishes luminesce. 4 TIMESLIFE-SIZE I recall a voyage I made as a college student many years ago from Ketchikan, Alaska, south through Queen Charlotte Sound to Bellingham, Washington. The vessel was a small salmon-fishing boat; it was mid-July and the sea was rough. I became violently seasick in the middle of the night and lunged from my bunk onto the deck. Ill though I was, I shall never forget the spectacular blaze on the crest of each break ing wave. The cause of this was a concentra tion of luminous single-celled dinoflagellates no bigger than needle points. Now in mid summer, they had reached the peak of their "bloom." Generally found in coastal waters rather than on the high seas, trillions of these minute gleamers were uniting to produce the amazingly fiery effect. Tiny Organisms Light Up a Bay Even smaller dinoflagellates can light up the sea. One of the most spectacular, Pyro dinium, swarms year round in a 60-acre bay near Parguera, Puerto Rico, on the island's southwest coast. Here on a moonless night the wake of a boat burns so brightly that the inlet has been named Bahia Fosforescente Phosphorescent Bay. Reach overboard, cup a handful of water, and your palm fairly daz zles. Fish dash away through the water, leaving cometlike trails (page 51).* Columbus, on his first trip to the New World, saw in Bahamian seas "a candle in motion," as he described it. This was possibly the marine fireworm Odontosyllis, whose ability to manufacture heatless light actually serves to preserve the species. A few days after the full moon, especially during the summer months, the female of this inch-long worm breaks out of her burrow in the coral and rises to the surface, glowing brightly. It is reasonably well established that her glow attracts the male, whose pursuit trig gers frenzied circling on the part of the female and the release of eggs in a luminously visible wake. The male, in turn, emits his sperm bearing fluids into this bright cloud of eggs. Some years ago, while working at the Uni versity of Hawaii's Coconut Island Marine Laboratory, I met author and biologist Dr. Frank Johnson of Princeton University, an authority on bioluminescence. Frequently during their summer-long stay, he and his wife Mary would set out at low tide to collect *Puerto Rico's Phosphorescent Bay was described and photographed in the author's July 1960 NATIONAL GEOGRAPHIC article, "Sailing a Sea of Fire."