Coral reefs scatter light like forests

Courtesy of Daniel Wangpraseurt

Coral reefs scatter light like forests

A coral reef has more in common with a forest than you might think. When sunlight strikes a group of trees, some parts tend to get more sun than others. Leaf tissue somewhat compensates for this by scattering light outward, helping to illuminate other leaves. A similar thing happens with coral, researchers reported at the American Geophysical Union’s Ocean Sciences meeting in New Orleans, Louisiana. When scientists shone a laser at a coral, the coral’s colorful tissue spread the light, generally redistributing it to other parts. Coral’s white calcium carbonate skeleton also gets in on the action. But it tends to spread light less, helping instead to focus it on specific areas that would otherwise be in the shade. Coral can also rearrange themselves depending on the circumstances, expanding to increase the spread of light or contracting to minimize it. Yet even with all of these tricks, light can only penetrate so far into coral tissue; it tends to drop off the deeper you go, as in forests, making getting by more difficult for cells at the bottom of tissue. So just as different cells in a leaf contain different amounts of chlorophyll, coral cells seem to house different amounts of the photosynthetic algae that makes their food, Symbiodinium. Cells specialized for low light to still make decent amounts of food in dim conditions, as measurements of photosynthesis (pictured here), showed. Snorkelers visiting coral may not notice the canopy below, a much smaller and subtler affair than the lofty bowers of forests on land. But the researchers argue that understanding it is crucial for understanding how life gets by on the sea floor.