Whereas a reef is merely a line of rocks in the tidal zone of a coast, and an artiﬁcial reef is just junk—from old railroad cars to scuttled destroyers—dumped for the beneﬁt of divers and sports ﬁshermen, a coral reef is a living underwater Xanadu constructed from the slowly, slowly growing exoskeletons of individual marine polyps. There are over two thousand species of soft and stony corals, and coral reefs—the most diverse ecosystems on Earth—harbor twenty-ﬁve thousand species of ﬁsh and other invertebrates. These extraordinary sea gardens survive within an exceedingly narrow range of water temperature, clarity, and purity. Warming ocean temperatures have caused deadly bleaching of corals; air, water, and land pollution—sewage runoff and the phospho-rus-laden, nutrient-rich wastewater produced by agriculture—endangers their survival further. A living reef erratically runs the length of the Florida Keys on the Atlantic side—the Keys themselves are ancient dead coral islands—and is increasingly being eaten away by a variety of diseases, its colorful complex world reduced to pallid rubble. Aspergillus is one of the most recent culprits in this decline; a fungus found in soil, it shreds coral as moths shred lace.