How Technology Lets Scientists See Hidden Colors in Marine Life

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Scuba diver carries elaborate photo equipment as he swims underwater.

Curator John Sparks and his colleagues have developed special lights, lenses, and filters to study biofluorescence underwater.

© K. McBurnie


Whether it’s listening to your dinner date at a busy bistro or reading right through “Showtime!” on the subway, New Yorkers—and humans in general—tend to be pretty good at focusing their attention and filtering out the noise. That sort of selectiveness is important to scientists as well. When studying the depths of the ocean or the reaches of outer space, Museum researchers are developing tools that help us shut out some of the data—and make it possible to discover things we never expected.

 

Shocking Pinks...and Greens and Oranges

Beneath the surface of the ocean, everything looks blue. That’s because once you’re 20 to 30 meters down, ocean water absorbs other colors of light—oranges, greens, reds, and yellows—and leaves the world cyan-hued—to us, that is. It turns out, we’re seeing blue because we’re looking at the underwater world through the eyes of land lubbers.

To natives of the seas, that world looks very, very different. It’s highlighted with biofluorescent light emitted by all kinds of fishes, corals, anemones, and even sea turtles. Molecules present in these organisms absorb the high-energy, blue-tinged sunlight that filters down to them and re-emit it in vibrant displays of orange, red, green, and yellow.

While these lightshows are technically visible to the human eye, they get lost in the ambient light of the Sun. That means they have been largely unseen—and unstudied—by scientists, until recently. Curator John Sparks and his colleagues have been developing new ways to keep out some wavelengths of light and better visualize these dazzling displays, and in 2014 they identified more than 180 species of biofluorescent fishes across 16 orders. In recent years, they’ve learned that turtles glow underwater, too.

Now, Sparks and team are refining specialized lights, lenses, camera housings, and filters to make it easier for researchers to better understand biofluorescence in marine organisms.

 

Close-up of small fish exhibiting a bioluminescent stripe and eye.

Under the right light, this fish may appear very different.

© D. Gruber


What the Fish Saw

To get a look at biofluorescence in action, Sparks and collaborators, including Yale neuroscientist Vincent Pieribone and Museum Research Associate David Gruber, try to get a fish-eye view.

How? By designing their equipment—including camera filters, which were developed specifically for underwater research—to see like a fish. The team can dissect the eyes of a fish specimen to learn which spectra of light a particular species can see underwater, then use that information to create filters that mimic that absorption spectra. The result is gear that lets the team experience the world the same way their research subjects do.

“Using these ‘fish-eye’ cameras, we can begin to better understand what other organisms see under water,” says Sparks.

“That has let us learn how catsharks, for example, can enhance their ability to communicate by producing green biofluorescent light. Light at these wavelengths is visible to other catsharks, but is otherwise filtered out at these depths.”

 

Brightly glowing fish surrounded by dark water.

Biofluorescence of Synodus dermatogenys.

J. Sparks, R. Schelly, W. Smith, M. Davis, D. Tchernov, V. Pieribone, D. Gruber


Perfect Dark

Sparks also studies underwater bioluminescence, in which organisms don’t require energizing blue light to make themselves seen. Instead, they produce light via chemical reactions—similar to the ones you can see every summer in the flicker of a firefly’s glowing abdomen.

Just as fireflies use their lights to communicate, some species of fishes and other marine organisms appear to use their bioluminescence to gain some advantage in the dark. Sparks and colleagues are researching this phenomenon. One factor that may be key to learning more about how fishes signal, hunt, and otherwise interact with one another using light is keeping those observations undetected. Dropping a shining LED into the midst of fishes that flash light signals at one another is, after all, pretty disruptive.

The current generation of deep-sea remotely operated vehicles—or ROVs, robots that scour the sea bottom for data—depends on some old-school tools to watch fishes under water: noisy motors, bright lights, and inelegant robotic grabbing arms. Even traditional nets can create pressure waves that disrupt delicate underwater ecosystems. That’s why Sparks and his colleagues are developing and using new tools to make the studies they conduct less noticeable to their subjects, including cameras that can shoot in ultra-low light.

“Using modern ultra-low-light cameras, you can film at night 200 meters below the surface of the ocean, and the small amount of light emitted from bioluminescent organisms can make it look like broad daylight,” says Sparks.

 

A version of this story originally appeared in the Fall 2017 issue of Rotunda, the Member magazine.