This coral falls into the ‘soft coral’ group, an octocoral, but it is a little strange for that grouping. This is because it is a reef building coral.
The coral is also a little misleading to the eye with its common name. It would be very understandable if an aquarist with a particular desire for a blue coral was looking for a coral that was actually blue! It isn’t. The external colour is a green tinged grey or brown and the polyps off-white. If the underside of the attached coral could be seen, then the blue would be also. If the skeleton is broken then again the blue would be seen. In other words the blue is internal. Another way of identifying this apparently hard coral is to note that there aren’t any corallites on the coral surface. Corallites are those circular areas that usually occur on a hard coral’s surface that contain the polyp.
Break an octocoral, surely they’re soft? This one isn’t, it could be mistaken for a hard coral. The link gives some pictures.
The common name as shown is blue coral, and they are also sometimes called the ridge coral. The proper name is Heliopora coerulea.
The coral is best placed in strong seawater movement and also under strong lighting, though it should be happy with medium movement and light as it is reasonably tolerant. The coral is also reasonably hardy, a word that pleases aquarists. It also has quite a fast growth rate, and could be ‘fragged’ should the aquarist wish.
The coral is common in the wild and there isn’t any current threat to it from collection.
This coral is a good addition to a well maintained reef aquarium and shouldn’t pose any particular problems. The coral is reported* to prefer warmer temperatures, between 80 and 84 deg F, so the aquarist who has obtained one could need to increase the seawater temperature slowly.
(*Reference: Aquarium Corals. Eric H. Borneman)