Wiedenmann was especially amazed because the shallow-water corals on the same reef only give off a green color. (See more stunning coral pictures.)
Corals generally get their glow from fluorescent pigments that act as sunblock. The sun’s intense rays, which can sunburn swimmers and divers that flock to these reefs, cause similar damage to coral and zooxanthellae, the symbiotic algae that lives inside coral.
Although bright sunlight at shallow depths can make the pigments hard to see with the naked eye, they can be visible if the coral makes lots of them, says Wiedenmann, who led a new study on the corals published June 24 in PLOS ONE.
Though these pigments are well studied, scientists hadn’t looked much at fluorescence in deeper dwelling corals, since they’re not as exposed to sunlight.
Which begs the question: Why were the Red Sea corals so colorful?