Remember a couple of posts ago, when I mentioned the glowing kitties, courtesy of the Nobel-Prize-winning GFP protein, and how it’s revolutionizing bio-imaging? GFP was first isolated from a jellyfish, but a substantial fraction of the stuff used in labs these days is derived from coral reefs. Coral, too, can fluoresce very prettily for the camera, in a wide range of hues, and the proteins that cause this are in the same family as GFP. Take this vision in purple, for example:
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In fact, the ocean environment is filled with light, not just from jellyfish and coral, but also some fish, some shells, bristleworms, and crabs, according to Charles Mazel of Physical Sciences, Inc. in Boston, who spoke this morning about his work on coral fluorescence imaging. He spent years making night-time dives to photograph coral reefs under UV light, armed with little more than an LED flashlight and a barrier filter fitted over his diving mask to block out any ambient light that would otherwise backscatter and ruin the image.
Eventually, with the dawn of the digital camera and the ability to limit exposure times, Mazel discovered that he didn’t need to dive in the dark anymore. He realized that the creatures’ fluorescence was all happening whenever the flash went off, and focusing on just that moment also removed the ambient light effects, without special shading. Voila! Now he could photograph coral reefs 24/7! In fact, it’s something of a hobby for many amateur aquarium enthusiasts, who keep sending Mazel their own stunning pix.
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Thanks to advances in fluorescent imaging, scientists are learning a lot more about its significance in the marine environment, according to Mazel, mostly because of the superior contrast and level of detail gained from the technique. It’s possible to tell the difference between various species of coral, for example, and between the coral and the symbiotic algae that live inside them, doing their bit to keep the food coming via photosynthesis. Also, “Little things that are difficult to see in natural light in a complex marine environment can be seen quite easily under fluorescence,” says Mazel — things like baby coral polyps, a strong indicator of the overall health of a coral reef.
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One question that hasn’t yet been answered is what function fluorescence is supposed to play biologically — although hypotheses abound. Maybe its purpose is to help capture light on behalf of the symbiotic algae so they can more efficiently go about their photosynthetic business, or perhaps it’s meant as a sort of “sunscreen” to protect the algae from excess light. Mazel doesn’t think either of those is likely — or at least not exclusive explanations. There’s even some evidence that fluorescence could play a role in coral spawning behavior.
Marine organisms most likely fluoresce for lots of different reasons, as Mazel discovered when he took his passion for marine fluorescence to the deep sea. He mounted a UV light on a submersible manned vehicle and descended 3000 feet, where he spotted a fluorescent sea anemone, a lizard fish, and snagged a first look at a fluorescent shark. A manta shrimp with fluorescent spots appeared to use them as part of its threat display — a defensive maneuver to warn off predators. I wouldn’t mess with the manta shrimp if I were a fish, however; aquarium owners know all too well that a manta shrimp will rapidly kill everything else in your tank.
