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Gregory R. Mann, Ph.D. {ret.}

Coral Reef

“Phylum cnidaria”

Coral Reefs are some of the most diverse ecosystems in the world, housing tens of thousands of marine species. About one-third of all marine fish species live part of their lives on Coral ReefsReefs in the Florida Keys for example, hold at least 45 species of Stony Coral, 37 species of Octocoral, five species of sea turtles, 500 species of fish, about 1,700 species of mollusks and hundreds of species of sponges. In addition to their incredible value as wildlife habitat, Coral Reefs protect coastlines from storms and provide billions of dollars of food and jobs every year to people around the world. Corals are ancient animals related to sea jellies and anemones. An individual Coral is known as a Polyp, a very small and simple organism consisting mostly of a stomach topped by a tentacle-bearing mouth. The Polyps extend their tentacles at night to sting and ingest tiny organisms. Thousands of identical Polyps live together and form a Coral colony. Each Polyp excretes a calcium carbonate exoskeleton beneath it and over long periods of time, the skeletons of many Coral colonies add up to build the structure of a Coral Reef. Many other species of fish, invertebrates, algae and microorganisms make their homes on and around this reef. Reefs only occur in shallow areas that are reachable by sunlight because of the relationship between Coral & Algae. 


Various types of microscopic Algae known as Symbiodinium live inside of the Coral, providing them with food and helping them to grow faster. In many ways, reef-building Corals are animals that act like plants – they stay in one place and get some of their energy from the sun. Coral Reefs are found all around the world in tropical and subtropical oceans. They are usually found in shallow areas at a depth of less than 150 feet. However, some Coral Reefs extend even deeper, up to about 450 feet deep. Despite how important Coral Reefs are to life in the ocean, all of them in the world add up to less than 1% of the sea floor, about an area the size of France. If you’ve ever visited an aquarium or gone snorkeling, you’re probably familiar with a wide variety of Corals. You may even know that Corals play a fundamental role in defining the structure of marine reefs, the most complex and diverse ecosystems in our planet’s oceans. But what many don’t realize is that these creatures, which resemble a cross between colorful rocks and various bits of seaweed, are in fact animals and amazing animals at that.

 

Interesting Facts

* Corals belong to the Phylum Cnidaria. Other animals that belong to the Phylum  Cnidaria include sea jellies (commonly called jellyfish which is not correct) hydrae and sea anemones. Cnidaria are invertebrates (they do not have a backbone) and all have specialized cells called nematocysts that help them capture prey and defend themselves. Cnidaria exhibit radial symmetry.

* Corals belong to the Class Anthozoa (a subgroup of the Phylum Cnidaria). Members of this group of animals have flower-like structures called polyps. They have a simple body plan in which food passes in and out of a gastrovascular cavity (stomach-like sac) through a single opening.

* Corals typically form colonies consisting of many individuals. Coral colonies grow from a single founder individual that divides repeatedly. A Coral colony consists of a base that attaches coral to a reef, an upper surface that is exposed to light and hundreds of polyps.

* The term “Coral” refers to a number of different of animals. These include Hard Corals, Sea Fans, Sea Feathers, Sea Pens, Sea Pansies, Organ Pipe Coral, Black Coral, Soft Corals, Fan Corals,  Brain Coral and Whip Coral.

* Hard Corals have a white skeleton that is made of limestone (calcium carbonate).Hard corals are reef builders and are responsible for the creation of the structure of a coral reef.

* Soft Corals lack the stiff limestone skeleton that hard corals possess. Instead, they have little limestone crystals (referred to as sclerites) embedded in their jelly-like tissues.

* Many Corals have zooxanthellae within their tissues. Zooxanthellae is algae that form a symbiotic relationship with the Coral by producing organic compounds that the Coral polyps use. This food source enables the Corals to grow faster than they would without the zooxanthellae.

* Corals inhabit a wide range of habitats and regions. Some solitary hard Coral species are found in temperate and even polar waters and occur as far as 6,000 meters below the surface of the water.

* Corals are rare in the fossil record. They first appeared in the Cambrian period (570 million years ago). Reef-building Corals appeared during the middle of the Triassic period (251 million years ago).

* Sea Fan Corals grow at right angles to the current of the water. This enables them to efficiently filter plankton from the passing water.

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