> Class Anthozoa > Subclass
Alcyonaria/Octocorallia > Order Helioporacea
learn only 3 things about them ...
They produce a hard skeleton but are considered members
of the group of soft corals because of the structure of
Their skeleton is blue on the inside. But don't break
the skeleton to see this!
are considered living fossils.
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
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
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
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 (0.2cm) in the
skeleton. They may be white or beige.
What do they eat? Blue
coral polyps harbour microscopic, single-celled symbiotic algae (zooxanthellae)
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 zooxanthellae
that give the animals their brownish colour.
This coral is preyed upon by a small nudibranch Doridomorpha gardineri.
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
With polyps extended.
Pulau Semakau, Mar 05
with branched tentacles
more typical of soft than hard corals.
Beting Bemban Besar, May 11
look inside a broken blue coral
showing the blue internal skeleton
and tiny channels when the polyps are.
Pulau Hantu, Apr 06
corals on Singapore shores
Pulau Biola, Dec 09
Terumbu Salu, Jan 10
Terumbu Berkas, Jan 10
Pulau Senang, Jun 10
Pulau Salu, Aug 10
Pulau Pawai, Dec 09
Pulau Berkas, May 10
Terumbu Raya, Mar 16
Photo shared by Marcus Ng on facebook.
Helioporidae recorded for Singapore
Y.C. and Peter K. L. Ng. 1994. A First Look at Biodiversity in
- Toh Chay Hoon & Rene Ong. 9 October 2015. New record of the nudibranch Doridomorpha gardineri in Singapore. Singapore Biodiversity Records 2015: 151-153
Ruppert, Richard S. Fox, Robert D. Barnes. 2004. Invertebrate
Brooks/Cole of Thomson Learning Inc., 7th Edition. pp. 963
Jan A., 2005. Biology
of the Invertebrates.
5th edition. McGraw-Hill Book Co., Singapore. 578 pp.
Katharina and Philip Alderslade, 2001. Soft
Corals and Sea Fans.
Australian Institute of Marine Science and the Museum and Art
Gallery of the Northern Territoriy. 264 pp
Harry and Daniel Knop. 2005. Corals:
Indo-Pacific Field Guide
IKAN-Unterwasserachiv, Frankfurt. 305 pp.
Eric H. 2001. Aquarium
Corals: Selection, Husbandry and Natural History
T.F. H Publications. 464 pp
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
- Ng, P. K.
L. & Y. C. Wee, 1994. The
Singapore Red Data Book: Threatened Plants and Animals of Singapore.
The Nature Society (Singapore), Singapore. 343 pp.