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The Fluorescence Of The Inhabitants Of The Ocean

Some travelers are discovering the ocean’s vast, yet often secretive, world of biofluorescence—a seascape where fish glow in lime-green patterns, corals sway in neon hues. Scientists have tuned into the phenomenon within the past 10 years, says marine biologist and National Geographic Explorer David Gruber. He has helmed several breakthroughs on the subject, including a 2019 study that found how animals create these glowing effects with molecules that were previously unknown to science. He worked on a 2014 study proving biofluorescence is widespread among more than 200 fish. His research has also shown that certain sharks and even reptiles, including sea turtles, display glow-in-the-dark powers—a revolutionary finding that was named one of National Geographic’s top 20 discoveries of the 2010s.

With biofluorescence, blue wavelengths of light hit the surface of an animal and are then emitted as a different color, usually vivid greens, oranges, and reds. This is different from bioluminescence, where animals such as jellyfish or fireflies generate their own light through a chemical reaction.

The ocean adds a layer of complexity to the phenomenon. While humans can see light in shades of red, green, and blue, our vision falters underwater. As the ocean gets deeper, certain wavelengths of color in the visible light spectrum are filtered out. At around 20 feet, red is gone. After 100 feet, it’s virtually all blue and green until you hit the light-free midnight zone, roughly 3,000 feet below the surface.

Many marine animals closer to the sea floor have evolved to have yellow eye filters that help them detect biofluorescence in other fish. Humans, however, need special equipment like yellow mask filters and blue dive lights to see these creatures glow in kaleidoscopic colors underwater.

Over the past decade, scientists have found evidence for biofluorescence in more than 200 species of fish, including two species of catsharks, and marine turtles. But with so little research on how and why these marine animals glow, scientists have more questions than answers. Likely theories for biofluorescence uses include interspecies communication, finding mates, camouflaging from predators, and hunting prey.

To chip away at these mysteries and better understand how light affects them, Gruber and his team create cameras that mimic the eyes of biofluorescent marine animals to see the world from their point of view. When they discovered biofluorescence in catsharks, they created a camera equipped with special filters to simulate how light hits their eyes. It unveiled two important insights: catsharks see the green biofluorescence they emit themselves, and they can increase the contrast of their fluorescent patterns.

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