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."

The biological systems that convert sunlight to photosynthesis and produce growth for nearly all organisms "are exactly the same way," he adds. Excess energy that cannot be used by the organism has to go somewhere, and Ackleson thinks it probably goes into fluorescence.

Thus the type and intensity of fluorescence emitted by marine organisms may offer critical clues about the health of the organisms, but much research has to be completed before anyone can say that with certainty.

For several years now scientists funded by Ackleson's program in the Office of Naval Research have been developing sensors that will detect and even analyze undersea fluorescence, even while divers are still in the water. Much of the research has been carried out in the Bahamas, and off a Hawaiian island formerly used as a bombing range, trying to answer a few fundamental questions.

"Are there indications in the fluorescence that could tell us this coral is under stress for some reason?" he asks. "It could still come back, it's still healthy, but it's under stress. That's what we're trying to get from fluorescence.

"Our only way of managing coral reefs at the moment is to look at a disaster that has already occurred and try to do something about it," he says. "We're trying to come up with a technique that will tell us, look, if you don't do something about it right now, a disaster will occur."

Coral reefs are critical habitats for marine life around the world, and they protect many beaches from erosion and coastal storms, so saving them is far more important than just an effort to protect these unique marine animals. They are animals, by the way, not plants. They are made up of trillions of microorganisms.

Seeking Old Bombs

There is another practical reason why Ackleson's program has been embraced by the Navy. Fluorescence might help searchers locate missing objects in the sea. Like a bomb.

Searching is frequently done by underwater cameras, but images are usually so cluttered with stuff that is of no interest to the searchers that zeroing in on the missing object can be a real challenge. But if that object doesn't fluoresce — and a bomb or a mine wouldn't — flashing a fluorescent light onto the sea floor should make it stand out in a maze of fluorescing organisms.

That concept has been tested in the Bahamas and Hawaii with considerable success.

Ackleson will take the equipment next year to one of the mysterious deep sea vents where strange forms of life flourish despite the lack of sunlight. With no sunlight, the organisms have no pigment which is critical to fluorescing, so "we shouldn't see any fluorescence at all," he says.

"So if we do see fluorescence, won't that be exciting," he says, "because we will have to figure out why."

Like he says, it's a voyage of pure discovery. Lee Dye’s column appears weekly on A former science writer for the Los Angeles Times, he now lives in Juneau, Alaska.