Dangerous dust kills coral.

Waiting for rains that never fall, West African farmers are watching soil turn to gray dust too powdery to grip plant roots. On the other side of the Atlantic Ocean, scientists are pondering why coral reefs in the Caribbean are dying. Could the two environmental disasters---4,800 km (3,000 mi) apart--be related?

Two scientists think so. Marine microbiologist Garriet Smith and geologist Gene Shinn were troubled by the massive destruction and death of coral reefs around the world. Together, they followed dusty clues to crack the case of the crumbling Caribbean coral.

The first clue came in 1996, when Smith focused his microscope on a type of coral called sea fan. He discovered a common soil fungus (parasitic plant like a mushroom or mold) called aspergillus (pronounced as-pur-JIH-lus) thriving on diseased sea fans, but not on healthy ones.

Was aspergillus making the sea fans sick? Only one way to know for sure. Smith injected the fungus into healthy sea fans---and the coral began to die.

Meanwhile, Shinn was working on his own coral theory. He knew that since the 1970s, drought had parched parts of Africa and turned entire regions into dusty deserts. Shinn also knew that powerful airstreams called trade winds lift about a billion tons of African dust every year, carry it on a five-day journey across the Atlantic, then dump the particles onto Caribbean waters and islands.

"The dustiest years were the main years coral was dying," says Shinn. Though Shinn suspected that the dust was making the corals sick, he didn't know how. That's when he came across a paper Smith had written about his fungus find. Shinn wondered: Was the airborne African dust dumping more aspergillus onto sea fans than the coral could tolerate?

Now, Smith thought Shinn was on to something. So he analyzed a sample of dusty Caribbean air, and found it loaded with aspergillus spores (fungus cells)! To make sure these spores were actually the ones causing the sea fan disease, Smith did a DNA analysis: He compared the DNA (the material that determines the unique genetic makeup of an organism) of the spores in the dust to the DNA of the sea fan aspergillus The result: a perfect match.

Excited by his successful sleuthing stint, Smith is now looking for causes of other coral diseases. "I want to find out which infections are caused by human activity," he says. If people know for sure how they're hurting coral, Smith believes, they may change their ways and help coral thrive.