Heliopora coerulea, known as blue coral, is a soft coral of the suborder Octocorallia and is the only species in the family Helioporidae (Obura et al. 2008). It is recognizable due to the bluish-gray coloration of its skeleton or corallum, which is made of crystalline aragonite, instead of the calcium carbonate that composes most coral skeletons (Bayer and Muzik 1997, Bourne 1881). Covering the skeleton is a thin layer of irregularly placed polyps that occupy cavities that extend into the main body cavity, which contains the striated stomach (Moseley 1875). Each polyp contains eight tentacles, thus, placing this coral in the suborder Octocorallia (Moseley 1875). The male and female gonads, which are separate, produce gametes that are dispersed on the tentacles (Harii et al. 2002). The planulae larvae, after brooding on the surface of the female, cleave from the surface and crawl to a new place of settlement near the parent colony (Babcock 1990). Their dispersal is restricted to the benthic level due to a lack of buoyancy, motile structures, and an energy source, such as zooxanthellae, which need sunlight (Harii et al. 2002). This lack of dispersal generates large Heliopora coerulea colonies (Bayer and Muzik 1997), with limited genetic variation, allowing the coral to be a potential victim of disease (Obura et al. 2008).
Heliopora is commonly found in the waters around Japan and Indonesia, but can be found all over the Indo-Pacific region (Obura et al. 2008). The geographical range of the coral is limited primarily by climate. It can survive in temperatures greater than 22°C, with its optimum temperatures being between 28°-29°C. This results in a distribution between the latitudes of 25° north and 25° south (Zann and Bolton 1985). Heliopora coerulea populations are threatened by the jewelry and aquarium trades, which have exploited the beauty of the color of the coral’s corallum (Obura et al. 2008). H. coerulea is also being threatened by the warming and acidification of the oceans that are causing coral bleaching (Zann and Bolton 1985).
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