The siphonophore Hippopodius, in an undated handout photo. The oceans are full of almost invisible animals, which use their transparency as a survival strategy, and the knowledge of deep-sea transparency could have practical applications. (Sonke Johnsen/Duke University via The New York Times) -- NO SALES; FOR EDITORIAL USE ONLY WITH STORY SLUGGED SCI FISH TRANSPARENCY BY KENNETH CHANG. ALL OTHER USE PROHIBITED.
As Sönke Johnsen scuba dives in the ocean, what he looks for is hard to see. He and his companions stare intently at one another, searching for distortions passing among them, slightly more visible against a dark wet suit. And then they carefully catch and place them in glass jars.
“You’d be surrounded with all these animals,” said Johnsen, a professor of biology at Duke. “But you could barely see them, because they were transparent.”
The oceans are full of almost invisible animals. To illustrate why, Johnsen began a recent talk with a macabre scenario: If a gunman burst into the room, people would scramble for cover behind chairs and walls. His point: There would be places to try to hide. Transparency is the most obvious strategy — if light passes straight through, no one can see you — and the one Johnsen first began researching almost 20 years ago. In graduate school, he had been studying clear biological tissues like the lenses in eyes. “I wanted to try to understand why they were clear,” he said.
By chance, his doctoral adviser mentioned that the open ocean was full of transparent animals. “Which was totally news to me,” he said.
He shifted his research focus from transparent tissues to transparent creatures. Transparency is not just a lack of pigmentation. Albinos, Johnsen points out, are not invisible; rather, the entire body must absorb or scatter as little light as possible.
Johnsen’s measurements of the see-through sea creatures found that 20 to 90 percent of the light passed through, undisturbed. “You could read a book through these animals,” he said.
The esoteric knowledge of deep-sea transparency could have practical applications. “A lot of what I learned about transparent animals, I then applied to human cataracts, which could ultimately help people out,” Johnsen said.