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A Glow in the Deep (video)
August 09, 2002

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Interviewees: Steve Ackelson, Office of Naval Research; Charles Mazel, Physical Sciences Inc./Nightsea.

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Produced by Sanjanthi Velu

Copyright © ScienCentral, Inc., with additional footage from the Office of Naval Research, the US Navy, and NOAA.

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The Navy might soon be getting a helping hand from mother nature when it comes to finding mines and bombs on the ocean floor.

This ScienCentral News video reports on how naval divers found corals emitting a strange glow, and how studying them could one day keep ships and subs safe from harm’s way.

Fluorescent corals

Although it has been known that some undersea creatures, including corals, will fluoresce when you shine the right light on them, very few people have actually seen this phenomenon underwater. Steve Ackleson, an optical oceanographer with the Office of Naval Research and Charles Mazel, principal research scientist with Physical Sciences Inc., are two of them.

"Fluorescence", says Ackleson, "is the absorption of light at one wavelength—say blue light—and the re-emission of a small portion of that light at another wavelength—say yellow, green or red." The corals they found seem to contain pigments that fluoresce. (Fluorescence should not be confused with bioluminescence. In fluorescence, the energy comes from the light that you shine on the object; in bioluminescence the energy comes from chemicals that are inside the animal.)

Corals are actually large colonies of tiny animals called polyps that build massive skeletons that form reefs. In order for corals to survive they depend on the single celled algae that grow inside them called "zooxanthellae." These algae provide the corals with food and energy through photosynthesis, while the corals provide nutrients and a safe environment for the algae.

There are several theories about why corals might have these fluorescent pigments. One is that they may be protecting the corals from bright light in shallow water. Mazel says that in dimmer conditions, the fluorescence process may take colors of light that are not useful for photosynthesis and convert them. Ackleson thinks its possible that corals are trying to communicate through their fluorescence. "In general", he says, "any plant or animal is highly colored for one of two reasons: they are either trying to attract organisms that are beneficial to them or they are trying to ward off other organisms that could be harmful to them." And he thinks corals may have evolved with these fluorescent pigments "to develop a relationship with those kinds of organisms".

Potential applications

Mazel, who is also the founder of a company called NightSea, has developed equipment for viewing and imaging fluorescence. He, Ackleson, and other navy divers have been diving with a laser imaging system fitted with lights and filters. When the seafloor is illuminated with blue light, and yellow-filters eliminate as much of the non-fluorescent light as possible, the corals fluoresce the brightest. The imaging system also allows them to measure the color and intensity of the fluorescence.

The potential applications of what they have observed in corals are immense. From an ecological perspective this method of imaging corals can be used to monitor the environment so that appropriate steps can be taken to protect the health of the reef. The researchers also noticed that if a coral is glowing, it is alive; if it is not glowing, the coral is dead. The imaging method can also be used to map the reef rapidly, and "at much higher detail than is possible to do with divers", says Ackleson.

by Sanjanthi Velu

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