The Miracle of the Reef

Coral spawn only once a year, and at night; how they manage to synchronize remains a mystery

Less than 20 years ago, conventional wisdom held that coral reefs did not propagate sexually, but passively and vegetatively, like some plants. Then in the mid 1980s scientists began to document a remarkable natural event. Once a year several species of reef-building corals spawn en masse, spewing out billions of eggs and sperm into the water. The discovery of this phenomenon has shed new light on the intricate workings of the reef and is especially significant in recent efforts to rebuild and reconstruct reefs, 10 percent of which biologists believe to be dead or severely damaged.

Although coral reefs are among the richest ecosystems in the world, and home to some 30 percent of known marine species, the massive animal-made structures are one of the planet's most fragile.

Writer John F. Ross joins a team of scientists, led by University of Miami research biologist Alina Szmant, on a series of night dives in the Florida Keys to collect reef spawn in order to study its development in the laboratory. Now that scientists know that coral reefs time their mass reproduction according to a lunar calendar, they are getting better at predicting spawning times, but how the corals synchronize their reproductive cycles to go off once a year remains a biological mystery.