Types of Coral Reefs, the Supreme Marine Structures

Abhijit Naik Jun 9, 2019
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A comprehensive write-up on the three major types of coral reefs - and their formation, intended to introduce you to one of the most fascinating, but less known attributes of the marine ecosystem. Continue reading for more facts about coral reefs - with emphasis on their types.
Coral reefs are marine structures which are made of calcium carbonate secreted by corals. Even though they occupy less than 10 percent of the total ocean surface, coral reefs are known to support as many as 25 percent of the total species found in the marine biome.
In terms of biodiversity, coral reefs are believed to be second only to the tropical rainforests of the world. However, many scientists refute this claim citing that the coral reefs are richer in terms of biodiversity as compared to the 'rainforests of the sea', with several species which depend on these marine structures yet to be discovered.

Coral Reef Facts

Coral reefs start at a length of a few centimeters and go on to attain an unimaginable size - the Great Barrier Reef in the Pacific Ocean being one of the best example of the same.
Coral reefs are considered largest living structures on the planet. The Great Barrier Reef which can be seen from the outer space, boasts of being the largest single structure made by living organisms. While coral reefs grow at the rate of 1 inch a year, they can only attain such gigantic size when they are not disturbed - by human activities in particular.
They are known to grow best in shallow, clear water, where there is no dearth of sunlight. It is very rare to find coral reefs growing below the depth of 40 meters or where some freshwater source meets the ocean. Coral reefs form an important component of the marine biome, and the lengthy list of coral plants and animals speaks volumes about the same.

Corals: Plants or Animals?

Even though corals appear as if they are plants, in true sense they are animals - marine colonial polyps to be precise, that are typically characterized by the presence of calcareous skeleton.
It is their shape which often leaves people wondering whether they are plants or animals, but once you take a note of the fact that what appears to be a plant is a full colony of corals, things become pretty clear. One of the basic attributes of animals which distinguish them from plants is their inability to prepare their own food.
Corals can't prepare their own food, but instead use their tentacles to hunt tiny organisms on which they feed. There exist two types of corals - hard corals and soft corals. While the hard corals, like the Elkhorn coral, which are armed with hard, limestone skeletons, contribute to the formation of coral reefs, soft corals do not have the ability to do so.

A Guide to Different Types of Coral Reefs

Though there exist several different types of coral reefs, most of the scientists only recognize the three major types among them - the fringing reef, the barrier reef, and the atoll.
These three types also find a mention in Charles Darwin's theory of coral reef formation wherein he gives a detailed description of each of them to show how they evolve. As you go through the details about these three major types and their formation, you will get to know several more facts about them.

Fringing Reefs

Typically characterized by its proximity to the shores, the fringing reef is one of the most common types of coral reef in the world.
It is located very close to the shore in such a manner that it forms a shallow channel or lagoon between its border and the shoreline. As this reef type forms very close to the shore, you seldom get to see it in regions where river drains into the ocean.
At times, this type of reef extends right to the edge of the shore and forms a continuous platform with it. Of the 3000 odd coral reefs which form the Great Barrier Reef around 700 are actually fringing reefs.

Barrier Reefs

The barrier reef is a type of coral reef which is separated from the mainland by a deep lagoon or a channel of water. It is not much difficult from the fringing reef, with the exception of the fact that it is located at a greater distance from the shore as compared to the latter.
One of the best examples of this type is the Great Barrier Reef, which covers approximately 133,000 sq miles of the Pacific Ocean. Scientists have seen a rise in the number of barrier reefs in the oceans of late, which, according to them, is attributed to rise in sea levels as a result of global warming.

Atolls

An atoll is a roughly circular, continuous barrier reef which extends all the way around a lagoon.
While the absence of a central landmass is a characteristic of this reef type, the absence of the same can be attributed to the rise in water level as a result of which the central island has submerged.
In other words, atoll reefs are formed when rise in water levels causes the central island to submerge while the coral structure continues to grow to keep up with the water surface. Even though such reefs are found in various parts of the world, they are most common in the Indo-Pacific region.
While these are the major coral reefs types that you get to see in oceans today, there also exist other types such as the 'patch reefs' which form within a lagoon and 'apron reefs' which are quite similar to fringing reefs but comparatively smaller in size.
The formation of coral reefs also prompts the formation of various other structures, with cays - small, low-elevation islands which are formed as a result of accumulation of sand on the coral reefs, being the best example of the same.
Other than being the most diverse, the coral reef ecosystem is one of the most fragile ecosystems on the planet - such that a slight change in ocean water temperature can cause severe harm to it. Threats to coral reefs exist in plenty, with climate change, overexploitation of reef resources, ocean pollution and harmful methods of fishing being a few of them.
Taking into consideration the biodiversity that this ecosystem boasts of, it would be utter foolishness to let the same deteriorate, and that makes the implementation of coral reef conservation measures the need of the hour.