Blue Coral

The blue coral is the only extant octocoral with a massive skeleton, which is composed of fibrocrystalline aragonite (calcium carbonate). It is a hermatypic zooxanthellaete species with either blue or green-grey polyps located within its skeleton, with each containing eight tentacles. Its colonies are either columnar, plate like or branched. It is a tolerant species and is used in marine aquariums.

Iron salts give the skeleton of Heliopora coerulea its unique color, which allows for easy recognition in fossil outcrops. As such, it is fairly abundant within paleontology, with fossils indicating the species has remained unchanged since the Cretaceous.

Blue coral has shown a particular resistance to thermal changes in its environment and has actually grown more in warmer temperatures.

Despite being common in some areas and having a large range, the blue coral has been given the conservation status of a vulnerable species by the IUCN. Its population is unknown but it is believed to be decreasing in line with the global destruction of coral reefs; it is threatened by aquarium harvesting, bleaching, habitat destruction, the acidification of oceans, and climate change. It is found in the eastern and western Indian Ocean, and the eastern central, western central, northwestern, and southwestern Pacific Ocean; its range includes the Great Barrier Reef, Australia, Japan and the Ryukyu Islands. Its largest colony is believed to be located off Ishigaki Island in the Yaeyama Islands, southwestern Japan. It is found in reefs with depths below 2 m (6.6 ft), or reefs exposed to waves, flats, intertidal regions, and sometimes in marginal habitats.