KEY LARGO, Fla. - Two gurgling scuba divers meander over the ocean floor, their motion slow, calculated, and delicate. In unison they rise partway up a towering, tree-shaped rack holding suspended coral fragments. Each gingerly picks a fragment, then descends to place it in the center of a circle surrounded by kneeling divers.

Another pair of divers repeats the procedure, then another. The scene appears mystical and pagan, as if the corals are talismans from the past and future.