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What are Sea Fans?

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  • Written By: N. Madison
  • Edited By: Bronwyn Harris
  • Last Modified Date: 25 November 2016
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Sea fans, also called gorgonians and sea whips, are nocturnal sea animals that look more like plants than animals. They are scientifically classified as belonging to the kingdom Animalia, the phylum Cnidaria, the class Anthozoa, the subclass Alcyonaria, and the order Gorgonacea. Sea fans are sessile, which means they cannot move around, and they are found exclusively in seawater environments. They live in oceans around the world. They are particularly suited to tropical and subtropical ocean water and are often found in shallow water near the state of Florida and places like Bermuda and the West Indies.

Sea fans consist of individual polyps that form colonies of the animals. These colonies normally stand vertically and appear flattened with branches, creating a fan-like look. However, they can sometimes appear bushy or look like whips. Sometimes they even appear encrusted. Colonies of sea fan polyps may grow to be many feet high and expand several feet across yet have only a few inches of thickness. Sea fans often appear in very bright colors, such as red, purple, and yellow.

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The sea fan suborder Holaxonia is the one that forms flexible, fan-like appearances, which are referred to as gorgonin. The suborder Scleraxonia, on the other hand, has a skeletal foundation made of calcium-like structures that form dense groupings. Some species behave more like coral, encrusting like coral does. However, most sea fans do not attach themselves to hard matter. Usually, sea fans take up residence in mud or sand, and some need up to 8 inches (20.32 centimeters) of sand in which to anchor.

There are eight tentacles on each sea fan polyp. They are used to catch plankton and other tiny particles, which are then consumed. The process by which they eat is called filter feeding. Their successful feeding can be helped when they are positioned against the current in the water. This allows them to maximize their food supply.

Sea fans are most often found in shallow water. However, there have been some living several thousand feet below the water's surface. The way they look and how large they grow seems to depend on where they are located. For example, they have a more fan-like shape and are more flexible are typically found in shallower water that has stronger currents. On the other hand, those that are taller, thinner and far less flexible are typically found in deeper water that has a calmer current.

Interestingly, other types of sea fauna take up residence within sea fan colonies. These include brittle stars and hydrozoa. The pygmy seahorse is known to live among the branches of certain types of sea fans. However, this seahorse looks a lot like its sea fan host and is able to camouflage itself in its home.

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aplenty
Post 3

@ GiraffeEars- One of the biggest threats to corals and other organisms that have calcium in their shells and bodies is ocean acidification. The increased amount of carbon in the atmosphere is the main source of the acidification of the oceans. The carbon dioxide mixes with precipitation in the atmosphere creating carbonic acid. This falls to the earth, drains into the oceans, and lowers the pH of seawater. The result is a mild acidification that is outside of the safe range for organisms like polyps, plankton, corals, and any other sea creature that lays eggs.

This has been happening forever, but the carbon pumped into the atmosphere through the burning of fossil fuels has increased the concentration of atmospheric carbon

, thus increasing the acidity of the rainwater. This carbonic acid is literally dissolving the creatures at the bottom of the food web along with the corals that shelter 25% of ocean biodiversity. I love the oceans, and I am glad that I will not be around to see an ocean devoid of life.
FrameMaker
Post 2

The sea fans you see for sale at so many ocean side tourist attractions are very similar to corals. There are two types of sea fan body structures of sea fans, being the rigid spindly type, or the flexible fanning gorgonians. The rigid sea fans are structured very similar to corals and they can attach to both the muddy sea floor, or rock and reef. The delicate lace looking sea fans form similar to corals, but they create their fanning flexible shape by forming a bony flexible substance called gorgonin. These fans almost exclusively attach to the muddy or sandy sea bottom.

GiraffeEars
Post 1

Sea fans come in some amazing colors and shapes. My mother has various mementos and knick-knacks from when we used to live in Negril, and in this collection are a number of sea fans and coral pieces. Some are bright red others are black and tan. They are over 25 years old, but they look like they were just plucked from the water yesterday. This amazes me since they are the remains of soft creatures that would wave in the currents. I would have never guessed that they would have lasted so long. Are sea fans related to corals? Do they form colonies on top of the shells of ancestral polyps, or is the whole fan made up of just one organism? What are the threats to sea fans and corals that are making so many die and bleach out across the globe?

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