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What is Coral?

Beautiful blue coral underwater.
Coral comes in all kinds of shapes and colors.
Vibrant pink coral.
Sea animals swimming near a coral reef.
A coral reef.
Divers must be careful not to accidentally inflict damage to coral reefs.
Coral often forms large structures, such as this ring-shaped atoll.
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  • Written By: Mary McMahon
  • Edited By: O. Wallace
  • Last Modified Date: 15 September 2014
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Coral is a marine organism in the class Anthozoa. There are over 2,000 species in this class, many of which form distinctive colonies of genetically identical organisms. Many people refer to these colonies as “coral,” and to the individuals inside the colonies as “polyps.” The organism plays a critical role in the marine environment, with collections of colonies known as reefs hosting around 25% of the known marine organisms, despite the fact that it is present on less than 1% of the ocean floor.

Individual polyps have soft bodies with a hard foot known as a calicle. They settle on the ocean floor, on a sandy or rocky substrate, depending on the species, and then they begin to build hard skeletons from the minerals present in seawater. Some polyps live as solitary individuals, but others reproduce through asexual budding, cloning numerous identical polyps to expand into a “coral head,” a large structure that can host hundreds or thousands of individual polyps, depending on how old it is.

Coral heads can take a variety of forms, depending on the species. Some are very hard, while others are soft, and a number of fantastic shapes from huge platters to sprouting antlers can develop. The landscape of a reef is often quite striking as a result.

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In addition to reproducing asexually through budding, corals can also reproduce sexually by spawning. When they spawn, they release clouds of eggs or sperm into the water, with gametes forming in these clouds when they drift together and eggs and sperm fuse. The resulting gametes free-float and develop into new polyps, which take root and repeat the process all over again.

Many of these organisms have a symbiotic relationship with zooxanthellic algae, algae that live inside the coral and photosynthesize, generating energy for the polyps. These algae are responsible for the distinctive colors of coral, with non-zooxanthellic ones being generally white to cream in color. In addition to gathering food and energy from the algae, they are also capable of trapping prey with sweeper tentacles covered in minute stinging cells.

Coral polyps look very similar to sea anemones, which is perhaps not too surprising, since the two are close relatives. These small organisms are very vulnerable to damage and changes in their environment, such as elevated temperatures, increased solar radiation, nutrient runoff, and human interference in the form of harvesting, trawling for fish, or accidental damage inflicted by divers and boats.

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lighth0se33
Post 8
I've seen coral jewelry that really doesn't look like it's made of coral. Some pieces are just beads made of coral that have been smoothed, rounded, and carved.

I saw a red rose pendant that I was surprised to learn was made of coral. I've also seen perfectly round beads of coral.

I've also seen necklaces that actually looked like bits of shell strung together. They are flat but have irregular edges and are stacked at angles to each other. This is a really popular type of cheap coral necklace.

I've read that the people who make this kind of jewelry only use the coral that washes up on the beach. I hope this is true, because I would hate to be wearing something that was harvested in a way that could harm the coral reefs.

giddion
Post 7

I think it's fascinating that coral can take so many different forms. I've seen some that look like bronchial tubes in the human body and others that look like tiny trees and a lot of shapes in between.

It all depends upon factors beneath the surface of the water. Coral is truly shaped by its environment, probably more so than many other kinds of undersea life.

wavy58
Post 6

@Perdido – Yes, my friend has living coral in her aquarium. I've seen everything from soft coral to mushroom coral in a tank before.

She has to keep the lighting and the water current at a certain level for the coral to do well. She also feeds the coral brine shrimp.

It's really a spectacular sight. Her aquarium looks like a section of the ocean floor. The color is stunning, and you really feel like you are looking at a television screen playing a show filmed with an underwater camera.

Perdido
Post 5

I've seen aquarium coral before, but I'm not sure if they are real. Can coral actually survive inside of a home aquarium? If so, what do you feed them?

Amphibious54
Post 3

@ Babalaas - You are quite right about the importance of coral reefs. 25% of all marine species live in coral reefs, and many species spawn in reefs and the lagoons they create. Loss of coral reefs can mean putting the 1 billion people who rely on seafood as their main source of protein in jeopardy of starvation. Because corals can be killed by rising water temperatures, subsistence fishing populations may ultimately be at the mercy of the actions of the developing and industrial world. However, there has been some action taken to protect the world's corals. I saw a recent show on National Geographic (I think) that drew attention to the problems of coral reef degradation, and coral bleaching. The show took an in-depth look at farming coral to seed dead or dying reefs. The results looked promising, and reefs were re-grown in only a couple of years. Let's hope that projects like this can help replace coral reefs as fast as they are dying.

Babalaas
Post 2

Coral reefs are home to so much of this planets biodiversity, yet there are so many threats to the worlds coral reefs. What happens if the world's coral reefs are lost? What can or is being done to protect these natural treasures?

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