Popular Science: The world is clobbering coral reefs, home to 25 percent of all marine species. Agricultural runoff pollutes the water around them; coastal developments tear them up; overfishing kills their inhabitants; and carbon dioxide emissions make the oceans too hot and acidic. In a provocative op-ed for the New York Times last year, Roger Bradbury, an ecologist at Australian National University, declared that reefs are zombie ecosystems . . . on a trajectory to collapse within a human generation. The slightly...