William Broad in The New York Times:
In 1932, William Beebe wedged his lanky body into a cramped submersible and became the first scientist to descend into the sea’s inky darkness. A tiny window let him gaze out. Later, he described an unfamiliar world of dancing lights, pale glows and beguiling shimmers. “It seemed to explode,” he said of one luminous creature. Nothing, he added in his book, “Half Mile Down,” had prepared him for the spectacular displays. The colors included pale greens, blues, reds and especially blue-greens, which by nature can travel far in seawater.
Over the decades, biologists learned that the creatures of the deep sea use light much as animals on land use sound — to lure, intimidate, stun, mislead and find mates. The living lights emanated from tiny fish with needlelike fangs, and gelatinous brutes with thousands of feeding tentacles. The sheer variety suggested that bioluminescence was fairly common, but no scientist came up with a measurement of the phenomenon. Now, 85 years after Dr. Beebe’s pioneering dive, scientists have succeeded in gauging the actual extent of bioluminescence in the deep ocean. During 240 research dives in the Pacific, they recorded every occurrence and kind of glowing sea creature — more than 500 types living down as deep as two miles. Then, the researchers merged the results into a comprehensive survey. The result? Most of the creatures — a stunning 76 percent — made their own light, vastly outnumbering the ranks of the unlit, such as dolphins. “People think bioluminescence is some kind of exotic characteristic,” said Séverine Martini, a marine biologist and lead author of the study, published this year in Scientific Reports. “Even oceanographers don’t realize that it’s common.”