This comes from the New York Times Science section, and is a nice synopsis of a research article published in this week's Science. There have been several articles in Science and Nature in the last month or so regarding coral biology and/or ecology, but this was one of the more interesting (I'm a little biased because of my research focus, but this seems to be a little more interesting to the general reefkeeping audience, too).
JM
That Special Underwater Glow
By HENRY FOUNTAIN
Published: August 17, 2004
Many coral colonies have a nice healthy glow about them, courtesy of fluorescent proteins produced by the coral animals themselves.
These proteins are the subject of much study because of their potential commercial uses. Most glow green when illuminated by researchers diving at night with blue lights.
But the glow from certain colonies of great star coral that a research team found in the Bahamas was different.
"This was daylight, 30 feet down, solar-stimulated, no extra lights," said Michael P. Lesser, a biologist at the University of New Hampshire who led the team. "It had an orange fluorescence that stuck out like a sore thumb."
Most important, as Dr. Lesser and his colleagues discovered through tests, the glow wasn't the work of the corals themselves. It was produced by cyanobacteria, also known as blue-
green algae, living inside them. The discovery is reported in the current issue of the journal Science.
The bacteria does much more than make for a colorful show, Dr. Lesser said. It appears to play a symbiotic role, fixing dissolved nitrogen in the seawater into a form that the coral can use.
"There have been a couple of studies that suggested there may be a role for bacteria in symbiotic association with coral," Dr. Lesser said. "We're the first ones to document conclusively that bacteria can live inside tissue of corals."
Corals are usually thought of as having a two-partner symbiosis between the coral animals and dinoflagellates, photosynthesizing algae that live within them. The algae produce food for the coral, but it is of limited value. "We call it the junk food diet," Dr. Lesser said. "Algal cells provide the carbon, but they never provide the nitrogen."
In the great star colonies studied, however, the cyanobacteria are part of the mix. "Now we have not just a simple two-way partnership, but a three-way," Dr. Lesser said. "And one of these partners can fix nitrogen."
The cyanobacteria may feed on glycerol produced by the dinoflagellates, and in turn may release some form of organic nitrogen for the coral. Or the coral may consume the cyanobacteria directly.
Dr. Lesser said further work is needed; for one thing, his team has yet to measure rates of nitrogen fixation by the cyanobacteria. So he is cautious in interpreting the results.
