sea fan

 

colonial marine animal forming erect, flattened, branching colonies in tropical and subtropical waters. Colonies may be several feet high and are often colorful, with purples, reds, and yellows predominating. The individuals, or polyps (see polyp and medusa), have eight feathery tentacles and feed on plankton organisms. Sea fans are classified in the phylum Cnidaria, class Anthozoa, order Gorgonacea.

It has been suggested that Sea whip be merged into this article or section. (Discuss)

Sea fans
Iciligorgia schrammi
Scientific classification
Kingdom: Animalia Phylum: Cnidaria Class: Anthozoa Subclass: Alcyonaria Order: Gorgonacea

A sea fan, or gorgonian, is a form of sessile colonial cnidarian, similar to a sea pen or a soft coral, found throughout the oceans of the world, especially in tropical and subtropical seawater. Individual tiny polyps form a colonies that are normally erect, flattened, branching, and reminiscent of a fan. Others may be whiplike, bushy, or even encrusting.^[1] A colony can be several feet high and across but only a few inches thick. They may be brightly coloured, often purple, red, or yellow.

Anatomy

The structure of a gorgonia colony varies. The suborder holaxonia skeletons are formed from a flexible, horny substance called gorgonin. The suborder scleraxonia variety of gorgonia are supported by a skeleton of tightly group calcareous spicules. There are also species which encrust like coral.^[2] Most of holaxonia and sclerazonia, however, do not attach themselves to a hard substrate. Instead, they anchor themselves in mud or sand.

Research has shown that measurements of the gorgonin and calcite within several long-lived species of gorgonia can be useful in paleoclimatology and paleoceanography, as the skeletal growth rate and composition of these species is highly correlated with seasonal and climactic variation.^[3][4][5]

Ecology

Each gorgonia polyp has eight tentacles which catch plankton and particulate matter that is consumed. This process, called filter feeding, is facilitated when the "fan" is oriented across the prevailing current to maximise water throughput and hence food supply.

Some gorgonia contain algae, or zooxanthellae. This symbiotically relationship assists in giving the gorgonia nutrition via photosynthesis. Gorgonia possessing zooxanthellae are usually characterized by brownish polyps. Those without zooxanthellae usually have more brightly colored polyps. Lacking this additional nutrion, they are more dependent on the nutrition they derive from filter feeding.

Gorgonia are found primarily in shallow waters, though some have been found at depths of several thousand feet.^[1][2] The size, shape, and appearance of the gorgonia are highly correlated with their location. The more fan-shaped and flexible gorgonia tend to populate shallower areas with strong currents, while the taller, thinner, and stiffer gorgonia can be found in deeper, calmer waters.^[1]

Other fauna, such as hydrozoa, bryozoa, and brittle stars, are known to dwell within the branches of gorgonia colonies.^[6] The Pygmy seahorse not only makes certain species of gorgonia its home, but closely resembles its host and is thus well camoflauged. ^[7]

Gorgonia are classified in the phylum Cnidaria, class Anthozoa, alongside the orders Alcyonacea (soft corals) and Pennatulacea (sea pens). There are about 500 different species of gorgonia found in the oceans of the world, primarily in the shallow waters of the Atlantic near Florida, Bermuda, and the West Indies.^[8]

References

1. ^ ^{a b c} Borneman, Eric H. (2001). Aquarium Corals: Selection, Husbandry, and Natural History. Neptune City, NJ 07753: T.F.H. Publications, 464. ISBN 1-890087-47-5. 
2. ^ ^{a b} Goldstein, Robert J. (1997). Marine Reef Aquarium Handbook. Barron's Educational Series, Inc., 198. ISBN 0-8120-9598-7. 
3. ^ Heikoop, J.M.; M.J. Risk, C.K. Shearer, V. Atudorei (2002-03). "Potential climate signals from the deep-sea gorgonian coral Primnoa resedaeformis". Hydrobiologia 471 (1-3): 117-124. DOI:10.1023/A:1016505421115. 
4. ^ Sherwood, Owen A.; Jeffrey M. Heikoop, Daniel J. Sinclair, David B. Scott, Michael J. Risk, Chip Shearer, Kumiko Azetsu-Scott (2005). Cold-Water Corals and Ecosystems, Erlangen Earth Conference Series. Springer Berlin Heidelberg, 1061-1079. DOI:10.1007/3-540-27673-4. ISBN 978-3-540-24136-2. 
5. ^ Bond, Zoë A.; Anne L. Cohen, Struan R. Smith, William J. Jenkins (2005-08-31). "Growth and composition of high-Mg calcite in the skeleton of a Bermudian gorgonian (Plexaurella dichotoma): Potential for paleothermometry". GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS 6. DOI:10.1029/2005GC000911. 
6. ^ Haywood, Martyn; Sue Wells (1989). The Manual of Marine Invertebrates. Morris Plains, NJ: Tetra Press:Salamander Books Ltd., 208. ISBN 3-89356-033-5. 
7. ^ Agbayani, Eli (2007-06-05). "Hippocampus bargibanti, Pygmy seahorse". FishBase. Retrieved on 2007-09-22.
8. ^ Sea Fan. University of Delaware Graduate College of Marine Studies. Retrieved on 2007-09-23.

Additional References

Sprung & Delbeek (1997), The Reef Aquarium, p. 31-32

External links

• The Marine Fauna Gallery of Norway

Donate to Wikimedia