In the watery world of national parks that touch the Caribbean Sea and the Straits of Florida, staghorn corals add some height to reefs. Their outstretched arms rise from the reefs, often mimicking elk or deer antlers to onlookers with some imagination. But since the 1970s more than 95 percent of these distinctive corals have died, and fears that they would vanish were growing. Now, though, research indicates that a vigorous transplanting initiative possibly could help recover the species.