Sea fan
Encyclopedia
A gorgonian, also known as sea whip or sea fan, is an order
of sessile
colonial
cnidaria
n found throughout the oceans of the world, especially in the tropics
and subtropics
. Gorgonians are similar to the sea pen
, another soft coral. Individual tiny polyp
s form colonies that are normally erect, flattened, branching, and reminiscent of a fan
. Others may be whiplike, bushy, or even encrusting. 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. Photosynthetic gorgonians can be successfully kept in captive reef aquariums.
. The suborder Scleraxonia variety of gorgonians are supported by a skeleton of tightly grouped calcareous spicules. There are also species which encrust like coral. 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 gorgonians can be useful in paleoclimatology
and paleoceanography
, as the skeletal growth rate and composition of these species is highly correlated with seasonal and climatic variation.
s 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 flow to the gorgonian and hence food supply.
Some gorgonians contain algae, or zooxanthella
e. This symbiotic relationship assists in giving the gorgonian nutrition via photosynthesis
. Gorgonians possessing zooxanthellae are usually characterized by brownish polyps. Those without zooxanthellae usually have more brightly colored polyps. Lacking this additional nutrition, they are more dependent on the nutrition they derive from filter feeding.
Gorgonians are found primarily in shallow waters, though some have been found at depths of several thousand feet. The size, shape, and appearance of the gorgonians are highly correlated with their location. The more fan-shaped and flexible gorgonians tend to populate shallower areas with strong currents, while the taller, thinner, and stiffer gorgonians can be found in deeper, calmer waters.
Other fauna, such as hydrozoa
, bryozoa
, and brittle stars, are known to dwell within the branches of gorgonian colonies. The Pygmy seahorse
not only makes certain species of gorgonians its home, but closely resembles its host and is thus well camoflauged.
Gorgonians 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 gorgonians found in the oceans of the world, primarily in the shallow waters of the Atlantic near Florida, Bermuda, and the West Indies.
Order (biology)
In scientific classification used in biology, the order is# a taxonomic rank used in the classification of organisms. Other well-known ranks are life, domain, kingdom, phylum, class, family, genus, and species, with order fitting in between class and family...
of sessile
Sessility (zoology)
In zoology, sessility is a characteristic of animals which are not able to move about. They are usually permanently attached to a solid substrate of some kind, such as a part of a plant or dead tree trunk, a rock, or the hull of a ship in the case of barnacles. Corals lay down their own...
colonial
Colony
In politics and history, a colony is a territory under the immediate political control of a state. For colonies in antiquity, city-states would often found their own colonies. Some colonies were historically countries, while others were territories without definite statehood from their inception....
cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
n found throughout the oceans of the world, especially in the tropics
Tropics
The tropics is a region of the Earth surrounding the Equator. It is limited in latitude by the Tropic of Cancer in the northern hemisphere at approximately N and the Tropic of Capricorn in the southern hemisphere at S; these latitudes correspond to the axial tilt of the Earth...
and subtropics
Subtropics
The subtropics are the geographical and climatical zone of the Earth immediately north and south of the tropical zone, which is bounded by the Tropic of Cancer and the Tropic of Capricorn, at latitudes 23.5°N and 23.5°S...
. Gorgonians are similar to the sea pen
Sea pen
Sea pens are colonial marine cnidarians belonging to the order Pennatulacea. There are 14 families within the order; they are thought to have a cosmopolitan distribution in tropical and temperate waters worldwide...
, another soft coral. Individual tiny polyp
Polyp
A polyp in zoology is one of two forms found in the phylum Cnidaria, the other being the medusa. Polyps are approximately cylindrical in shape and elongated at the axis of the body...
s form colonies that are normally erect, flattened, branching, and reminiscent of a fan
Fan (implement)
A hand-held fan is an implement used to induce an airflow for the purpose of cooling or refreshing oneself. Any broad, flat surface waved back-and-forth will create a small airflow and therefore can be considered a rudimentary fan...
. Others may be whiplike, bushy, or even encrusting. 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. Photosynthetic gorgonians can be successfully kept in captive reef aquariums.
Anatomy
The structure of a gorgonian colony varies. The suborder Holaxonia skeletons are formed from a flexible, horny substance called gorgoninGorgonin
Gorgonin is a complex protein that makes up the horny skeleton of the holaxonia suborder of gorgonians. It frequently contains appreciable quantities of bromine, iodine, and tyrosine.-Scientific use:...
. The suborder Scleraxonia variety of gorgonians are supported by a skeleton of tightly grouped calcareous spicules. There are also species which encrust like coral. 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 gorgonians can be useful in paleoclimatology
Paleoclimatology
Paleoclimatology is the study of changes in climate taken on the scale of the entire history of Earth. It uses a variety of proxy methods from the Earth and life sciences to obtain data previously preserved within rocks, sediments, ice sheets, tree rings, corals, shells and microfossils; it then...
and paleoceanography
Paleoceanography
Paleoceanography is the study of the history of the oceans in the geologic past with regard to circulation, chemistry, biology, geology and patterns of sedimentation.- Source of information :...
, as the skeletal growth rate and composition of these species is highly correlated with seasonal and climatic variation.
Ecology
Each gorgonian polyp has eight tentacleTentacle
A tentacle or bothrium is one of usually two or more elongated flexible organs present in animals, especially invertebrates. The term may also refer to the hairs of the leaves of some insectivorous plants. Usually, tentacles are used for feeding, feeling and grasping. Anatomically, they work like...
s which catch plankton
Plankton
Plankton are any drifting organisms that inhabit the pelagic zone of oceans, seas, or bodies of fresh water. That is, plankton are defined by their ecological niche rather than phylogenetic or taxonomic classification...
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 flow to the gorgonian and hence food supply.
Some gorgonians contain algae, or zooxanthella
Zooxanthella
Zooxanthellae are flagellate protozoa that are golden-brown intracellular endosymbionts of various marine animals and protozoa, especially anthozoans such as the scleractinian corals and the tropical sea anemone, Aiptasia....
e. This symbiotic relationship assists in giving the gorgonian nutrition via photosynthesis
Photosynthesis
Photosynthesis is a chemical process that converts carbon dioxide into organic compounds, especially sugars, using the energy from sunlight. Photosynthesis occurs in plants, algae, and many species of bacteria, but not in archaea. Photosynthetic organisms are called photoautotrophs, since they can...
. Gorgonians possessing zooxanthellae are usually characterized by brownish polyps. Those without zooxanthellae usually have more brightly colored polyps. Lacking this additional nutrition, they are more dependent on the nutrition they derive from filter feeding.
Gorgonians are found primarily in shallow waters, though some have been found at depths of several thousand feet. The size, shape, and appearance of the gorgonians are highly correlated with their location. The more fan-shaped and flexible gorgonians tend to populate shallower areas with strong currents, while the taller, thinner, and stiffer gorgonians can be found in deeper, calmer waters.
Other fauna, such as hydrozoa
Hydrozoa
Hydrozoa are a taxonomic class of very small, predatory animals which can be solitary or colonial and which mostly live in saltwater. A few genera within this class live in freshwater...
, bryozoa
Bryozoa
The Bryozoa, also known as Ectoprocta or commonly as moss animals, are a phylum of aquatic invertebrate animals. Typically about long, they are filter feeders that sieve food particles out of the water using a retractable lophophore, a "crown" of tentacles lined with cilia...
, and brittle stars, are known to dwell within the branches of gorgonian colonies. The Pygmy seahorse
Pygmy seahorse
The pygmy seahorse, also known as Bargibanti's seahorse, is a seahorse of the family Syngnathidae found in the western central Pacific Ocean. It is tiny, usually less than in size and lives exclusively on fan corals. There are two known color variations: grey with red tubercles, and yellow with...
not only makes certain species of gorgonians its home, but closely resembles its host and is thus well camoflauged.
Gorgonians are classified in the phylum Cnidaria
Cnidaria
Cnidaria is a phylum containing over 9,000 species of animals found exclusively in aquatic and mostly marine environments. Their distinguishing feature is cnidocytes, specialized cells that they use mainly for capturing prey. Their bodies consist of mesoglea, a non-living jelly-like substance,...
, class Anthozoa
Anthozoa
Anthozoa is a class within the phylum Cnidaria that contains the sea anemones and corals. Unlike other cnidarians, anthozoans do not have a medusa stage in their development. Instead, they release sperm and eggs that form a planula, which attaches to some substrate on which the cnidarian grows...
, alongside the orders Alcyonacea (soft corals) and Pennatulacea (sea pens). There are about 500 different species of gorgonians found in the oceans of the world, primarily in the shallow waters of the Atlantic near Florida, Bermuda, and the West Indies.