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| cnidarians text index | photo index |
| Phylum Cnidaria > Class Anthozoa > Subclass Alcyonaria/Octocorallia > Order Helioporacea |
| Blue
coral Heliopora coerulea Family Helioporidae updated Aug 10
Where seen? These living fossils are commonly seen on our Southern shores, sometimes forming large colonies. Among hard corals. What are blue corals? Blue corals belong to Phylum Cnidaria. Although they produce a hard skeleton, they are NOT hard corals and are more closely related to soft corals. Blue corals are the only members of the Order Helioporacea, Family Helioporidae. They are also the only members of the soft corals (Subclass Alcyonaria) that contributes to reef-building, like hard corals do. Living fossil: Blue corals are considered living relicts of fossil species known from more than 100 million years ago. Most other corals have an evolutionary age of only several hundred thousand years. Blue corals used to be dominant before the last Ice Age when the seas were warmer. They are now only found in warm tropical waters. Features: Blue corals are confusing. Firstly, they are often brown and don't appear blue at all. Secondly, although they have a hard skeleton, they are not grouped with other hard corals. Colonies 15-30cm, polyps about 0.5cm. Their internal skeletons are blue, hence their common name. The blue colour is due to the iron salts that are incorporated into their skeletons. On the outside, they are usually brown because the thin layer of brownish living tissue that covers the outer surface of the skeleton. The skeletons are made of a different kind of calcium carbonate (fibro-crystalline argonite) that is more brittle than that of true hard corals that belong to Subclass Sclerectinia. Inside the skeleton are tubes where the long, thin polyps live and a system of canals. Blue coral colonies are usually boulder shaped with knobs. They may also have thick leaf-like forms or columns, and may even be encrusting or plate-like. Tiny polyps (about 0.5cm) have 8 tentacles with fine branches like other soft corals (True hard coral polyps have smooth tentacles in multiples of six). The polyps stick out of tiny holes in the skeleton. They may be white or beige. What do they eat? Blue coral polyps harbour microscopic, single-celled symbiotic algae (zooxanthallae) within their bodies. The algae undergo photosynthesis to produce food from sunlight. The food produced is shared with the host, which in return provides the algae with shelter and minerals. It is the zooxanthallae that give the animals their brownish colour. Status and threats: Blue corals are not listed among the threatened animals of Singapore. However, like other creatures of the sea, they are threatened by human activities that degrade or destroy the habitat. |
 Pulau Jong, Jul 07  Tiny clam found in the coral.  Polyps with branched tentacles more typical of soft than hard corals. St. John's Island, Sep 04  A look inside a broken blue coral showing the blue internal skeleton and tiny channels when the polyps are. Pulau Hantu, Apr 06 |
They produce a hard skeleton but are considered members
of the group of soft corals because of the structure of
their polyps.
Their skeleton is blue on the inside. But don't break
the skeleton to see this!Blue corals on Singapore Shores
 Pulau Hantu, Apr 06 |
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 Pulau Semakau, Mar 05 |
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 Pulau Semakau, Mar 05 |
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more photos of blue corals on Singapore shores
part 1 | part 2 | part 3 | part 4 | part 5 | part 6 | part 7
| Family
Helioporidae recorded for Singapore from Wee Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
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References
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Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963 |
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