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Some living sea fans can be seen at the coral rubble area. Sea fans
are the more delicate members of the coral group. They can be seen
at the seaward edge of the coral rubble area which is less often exposed
at low tide.
Sea fans (also called gorgonians) belong to the same group as sea
anemones and soft corals. While sea anemones are large solitary polyps,
a sea fan is a colony of tiny polyps that are linked one another.
Unlike soft corals where the polyps are connected by a soft tissue
mass, in sea fans, the individual tiny polyps are supported by a central
rod made of a combination of sclerites (tiny pieces of calcium carbonate)
and a tough but flexible protein called gorgonin.
Sea fans usually grow as branching, tree-like forms. Although they
have a skeleton, this is usually more flexible than the solid calcium
carbonate skeletons of hard corals.
Colonial food: Studies suggest
sea fan polyps have few stinging cells and feed on particles tinier
than zooplankton. Sea fans usually grow so their branches are at right
angles to the flow of the current. This maximises the amount of water
they filter. A few shallow-water sea fans harbour zooxanthellae (symbiotic
single-celled algae) inside their polyps. These carry out photosynthesis
and contribute nutrients to the host polyp.
Sea fan babies: Sea fans usually
reproduce asexually: new polyps bud off to enlarge the colony. Some
sea fans purposely nip off a portion that breaks off and drifts away
to settle down elsewhere and expand into a new colony. Sea fans also
reproduce sexually. The polyps may produce sperm or eggs. The eggs
develop into free-swimming larvae that drift with the plankton before
settling down to start a new colonies.
Role in the habitat: All kinds
of small animals live on sea fans including tunicates, barnacles,
clams, snails and gobies. Some of these small animals prey on the
sea fan. These animals usually take on the shape and colour of their
host. |
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Orange sea fan
Subergorgia suberosa
Close up of
Orange sea fan
Red sea fan
Close up of polyps |
See
also ...
Cnidarians in general
Links
Gorgonians are
corals too on the Florida Keys National Marine Sanctuary website: an
introduction to gorgonians.
Biology
and ecology of gorgonians on the Big Bank Shoals of the Timor Sea on
the Australian Institute of Marine Science website: introduction to gorgonians
in general with lots of photos.
Other references
- Lim, S., P. Ng,
L. Tan, & W. Y. Chin, 1994. Rhythm of the Sea: The Life and Times
of Labrador Beach. Division of Biology, School of Science, Nanyang
Technological University & Department of Zoology, the National University
of Singapore. 160 pp.
- Barnes, Robert
D. & Ruppert, Edward E., 1996. Invertebrate Zoology. Harcourt
College Publishers. 6th Edition. pp. 1056, G-1-16, I-1-30.
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