Researchers Use Fluorescence to Study Coral Reefs

Steve Ackleson could hardly believe his eyes the first night he took his sophisticated instruments down into the murky depths off the coast of Florida.

As he shined his blue light on the coral reefs, they suddenly came alive with fluorescence, glowing in strange colors as a new world opened before him.

"We had no idea what we were going to find," he says now, several years after that first experience. "This was pure discovery."

Ackleson is an optical oceanographer with the Office of Naval Research, and what he found that day — and has found over and over again in other dives — is a new way of looking at marine life, a way that could have widespread applications. It may even give scientists a new way of finding which coral reefs around the world are losing the battle for survival before it's too late to do anything about it. Or it may help the military find a missing bomb, lost in the clutter of marine organisms off a populated coast.

Like an astronomer with a new camera that captures images that cannot be seen by the human eye, Ackleson is looking at the universe under the sea with cameras that "see" colors that aren't normally there.

Fluorescent Night Dives

Ackelson's voyage of discovery began in 1995 when he got his hands on a nifty underwater sensor that could image the ocean floor at various wavelengths. As a scientist who studies the way light interacts with the ocean, he realized the sensor could open a new field of research.

"The sensor was designed for other reasons, but we thought, my gosh, we could look for fluorescence," he says.

So he and several colleagues equipped the sensor with filters that could remove light of unwanted wavelengths, or colors, and they entered the sea with a powerful blue light. The dives, usually done at night to eliminate light from the sun, were designed to see what would happen if they shined the blue light on marine organisms. If coral fluoresces, for example, it should emit light of different wavelengths than seen when the coral is illuminated by sunlight.

"What came back was imagery of these fantastic fluorescent fields in different colors," he says.

The color of the fluorescence was so vivid that the divers soon realized they could distinguish between different coral species on the basis of color, and the intensity was so great that it might tell which corals are robust, and which are dead or near death. It was a significant finding, because coral reefs around the world are dying from pollution, changing water temperatures, poaching, and possibly reasons we haven't even detected.

Why they fluoresce is somewhat of a mystery. Lots of marine organisms use their own biological systems to produce light, called bioluminescence, and it's usually done for very specific purposes, like attracting a mate. But fluorescence is something else entirely. When light falls on coral, for example, the coral absorbs most of that light, converting it into biomass, but some of it gets re-emitted as fluorescence.

Some scientists, including Ackelson, believe fluorescence results from the inability of the organism to use or store all of the energy it receives from the light.

Inefficient ‘Engines?’

"It's kind of like a car engine," he says. "Some of the energy from the gasoline makes the car go, some of it goes to making the engine hot, some of it goes to making stuff that comes out of the tailpipe, and some of it goes to making sounds. It's not totally efficient."

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