Cnidaria > Class Anthozoa
> Subclass Alcyonaria/Octocorallia > Order
fans or Gorgonians
updated Mar 13
learn only 3 things about them ...
They are animals and not plants! Don't break or step on
Each fan is a colony of tiny polyps that produce a hard
fascinating animals live on them. Look for them.
seen? Most people are surprised to learn that sea fans
are still quite commonly seen on our shores. Large colonies may be
seen on undisturbed intertidal reefs in the North. But smaller ones
may be seen even on Changi and East Coast Park. Divers may encounter
large sea fans on our Southern islands.
What are gorgonians? These beautiful
delicate creatures are often mistaken for plants. Gorgonians belong
to Phylum Cnidaria which includes
the more familiar sea anemones, hard corals and jellyfishes. Gorgonians
are members of the soft coral group (Subclass Alcyonaria/Octocorallia).
There are about 18 families of gorgonians.
Features: A gorgonian is a colony
of small polyps. Each polyps is about 0.5cm or smaller, usually white
or transparent. Like other soft corals, each polyp has 8 branched
Unlike other soft corals, the gorgonian polyps are supported by a
central rod made of a tough but flexible protein called gorgonin that
is similar to the material produced in the horns of animals. Many
species incorporate calcium into the gorgonin.
Some reinforce this further with an arrangement of sclerites
(tiny bits of calcium). Although a sea fan has a skeleton, this is
usually more flexible than the solid calcium carbonate skeletons of
hard corals. The living polyps share a thin skin over this support.
Gorgonian colonies usually take on branching forms, but the branching
is only along one plane (i.e., most are not bushy). Thus, these colonies
are usually called sea fans. Others are unbranched and grow into one
long whip-like form, and are called sea whips.
Colonial food: Studies suggest gorgonian polyps
have few or weak stinging cells and feed on particles tinier than
zooplankton; such as phytoplankton and bacteria. Prey that are too
big or struggle too vigorously are released by the polyps.
A sea fan usually grows so that the branches are at right angles to
the flow of the current. This maximises the amount of water filtered
and apparently breaks up the water current into curls that wash back
over the polyps, for a second chance to filter out more edible bits.
Sea fans are most abundant and grow largest where there is a strong
A few shallow-water sea fans like the Leathery
sea fan harbour zooxanthellae (symbiotic single-celled algae)
inside their polyps. These carry out photosynthesis and contribute
nutrients to the host polyp. But most gorgonians do not have zooxanthellae
and are thus able to grow in shadier places or murkier water.
Sea fan babies: For most species,
each sea fan colony is usually either male or female. In most species,
the females brood the eggs. Some brood the eggs internally, while
others brood them in mucus pouches on the surface of branches.The
eggs develop into free-swimming planula larvae that drift with the
plankton before settling down to start a new colonies.
Gorgonians sometimes also reproduce by budding off new polyps to enlarge
the colony. Some gorgonians purposely nip off a portion that breaks
off and drifts away to settle down elsewhere and expand into a new
colony. Some sea whips reproduce by dropping off a branch tip that
'roots' and starts a new colony.
Role in the habitat: All kinds
of small animals live on gorgonians including tunicates, barnacles,
clams, snails (such as the ovulids),
tiny shrimps, brittle
stars and gobies. Hermit
crabs have also been seen clinging to sea fans. Some of these
small animals prey on the sea fan. These animals usually take on the
shape and colour of their host.
Human uses: Gorgonians, especially
fan-shaped ones, are harvested for the live aquarium trade or sold
dried as ornaments. "Red coral" that is harvested for jewellery
is a gorgonian that is found in the Mediterranean Sea and Sea of Japan.
Gorgonians are notoriously difficult to maintain artificially in an
aquarium and may release toxins that kill off tank mates.
and threats: Gorgonians are not listed among the endangered
animals of Singapore. However, like other animals harvested for the
live aquarium trade, most die before they can reach the retailers.
Without professional care, most die soon after they are sold. Those
that do survive are unlikely to breed successfully. Like other creatures
of the intertidal zone, they are affected by human activities such
as reclamation and pollution. Trampling by careless visitors, and
overharvesting also have an impact on local populations. Abandoned
fishing lines can also uproot living sea fans.
sea fans dot the rocks.
East Coast Park, Jun 06
sea fans seen on remote shores.
Beting Bronok, Jun 04
of a sea fan.
Tuas, Dec 11
snails on a sea fan
East Coast, Jun 06
colourful brittle stars.
Changi, Jul 09
and tangled in fishing lines
Changi, May 06
fans on Singapore shores
Gorgonacea recorded for Singapore
N.K.C. and Chou, L.M. 20 December 1996. An annotated checklist
of the gorgonians (Anthozoa: Octocorallia) of Singapore.
Groups from Fabricius, Katharina and Philip Alderslade, 2001. Soft
Corals and Sea Fans.
*from Sih, Justin Sih and Jeff Chouw. 31 Dec 2009. Fish and whips:
Use of gorgonians as a habitat by the Large Whipcoral Goby Bryaninops
+from our observation.
Solenocaulon sp. B
sp. (Flat branch
Acanthogorgia sp. B
Acanthogorgia sp. C
sp. (Skinny sea fan)
Astrogorgia cf. rubra
Astrogorgia cf. sinensis
Astrogorgia sp. A
Astrogorgia sp. B
Echinomuricea pulchra (Gnarled
sp. (Maze sea fan)
Echinogorgia sp. A
Echinogorgia sp. B
Echinogorgia sp. C
Echinogorgia sp. D
Echinogorgia sp. E
Echinogorgia sp. F
sp. (Candelabra sea fan)
Euplexaura cf. pinnata
Euplexaura sp. A
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.
- Goh, N.K.C.
and Chou, L.M. 20 December 1996. An
annotated checklist of the gorgonians (Anthozoa: Octocorallia)
of Singapore, with a discussion of gorgonian diversity in the
Indo-West Pacific. Raffles
Museum Bulletin of Zoology Pp. 435-459.
L.P. van, N.K.C. Goh & L.M. Chou. The
Melithaeidae (Coelenterata: Octocorallia) of Singapore.
Zool. Med. Leiden 73 (19), 6.iii.2000: 285-304, figs 1-13. ISSN
- Nigel K. C. Goh, Peter K. L. Ng
and L. M. Chou. 1999. Notes
on the shallow water gorgonian-associated fauna on coral reefs
in Singapore Bulletin of Marine Science, 65(1): 259-282.
- Sih, Justin
Sih and Jeff Chouw. 31 Dec 2009. Fish
and whips: Use of gorgonians as a habitat by the Large Whipcoral
Goby Bryaninops amplus (Larson),
Raffles Bulletin of Zoology Supplement No. 22 : 145-157.
- Edward E.
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.
- Wee Y.C.
and Peter K. L. Ng. 1994. A First Look at Biodiversity in Singapore.
National Council on the Environment. 163pp.
G.W. H. and P. K. L. Ng and Ho Hua Chew, 2008. The Singapore
Red Data Book: Threatened plants and animals of Singapore.
Nature Society (Singapore). 285 pp.