What Are Coral Reefs?

Coral reefs are like underwater cities made of tiny animals called “coral polyps.” Stony corals make up most coral reefs. 

  • Coral reefs form in shallow waters of tropical and subtropical regions.
  • The coral reef ecosystem provides a habitat for a variety of marine life.
  • The coral polyp has a mouth surrounded by tentacles with stinging cells to capture prey.
  • The coral polyp has a symbiotic relationship with a type of algae. The polyp provides a protected environment for the algae to live in, and the algae provides nutrients through photosynthesis. 

Types of Coral Reefs

There are three main types of coral reefs based on their location and structure.

  • Fringing Reefs are the most common and are found near the shore. They directly connect to the land, and the outer edges extend towards the sea,
  • Barrier Reefs are separated from the shore by a lagoon. They are larger and several miles wide.
  • Atolls are circular or oval-shaped reefs that encircle a lagoon. They are found in the open ocean, far from land. They form on the submerged rims of volcanic islands.

How Are Coral Reefs Formed?

Coral reefs form through a slow and continuous process that takes thousands or even millions of years.

  • Coral larvae can swim and settle on hard substances like rocks or dead coral skeletons.
  • The coral larvae evolve into a small, tube-shaped organism called a coral polyp. Each polyp produces an identical clone, slowly forming a colony. 
  • The coral polyp secretes a hard exoskeleton made of calcium carbonate. The calcium and carbonate ions come from the surrounding seawater.
  • These coral skeletons accumulate over time to form a sturdy reef structure. 

Why Are Coral Reefs Important?

Coral reefs are incredibly important for various reasons.

  • Biodiversity Hotspot – They provide habitats and breeding grounds for several fish species and other marine life. Coral reefs support 25% of ocean life.
  • Fisheries – They provide food to the coastal communities.
  • Coastal Protection – They protect coastlines from the impact of waves, erosion, and storms by acting as a natural barrier.
  • Medicinal Resource – Marine animals living in the reefs have helped in scientific research to discover treatments for cancer and arthritis.

Fun Facts

Here are some interesting facts about coral reefs:

  • The largest island of coral formation is Christmas Atoll in the west-central Pacific Ocean.
  • The Great Barrier Reef in Australia is the world’s largest coral reef system. It is so large that it can be seen from space.
  • Coral reefs grow at the rate of about 0.4 to 1.2 inches per year. Reefs take thousands to millions of years to reach their full size.
  • There are hundreds of coral species of all colors and sizes. Brain corals resemble human brains, with maze-like patterns weaving across their shape.


Let’s quickly recap what we learned about coral reefs:

  • What are coral reefs made of? Coral Polyps
  • Where are coral reefs found? Shallow Waters of Tropical and Subtropical Regions
  • What are the three main types of coral reefs?  Fringing Reefs, Barrier Reefs, and Atolls
  • What is the hard exoskeleton of a coral reef made of? Calcium Carbonate
  • What percentage of ocean life is supported by coral reefs? 25%
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