A diver is silhouetted against the sunlit surface as hundreds of schooling baitfish cluster around a large outcropping of black coral. At about one inch of growth per year, black coral is one of the slowest growing corals on the reef.  Once thought to have the power to cure disease, the polished ebony skeleton of this variantly-colored family of corals is used to make jewelry in many parts of the world. In the US state of Hawaii, for example, it is unfortunately designated as the state gem [Waikiki aquarium PDF file], a controversial label which can only help contribute to its scarcity.  Fortunately for its survival, black coral thrives at depths over 100 feet-- considered deep by sport divers, though advances in dive technology are diminishing this natural obstacle to black coral collection (as noted in the Honolulu Star-Bulletin).  Black corals belong to order Antipatharia, which literally means "against disease". Coral identification: Antipathes sp.