What are coral reefs?

coral reefs

Coral reefs are colonies of tiny living creatures that are found in oceans.

They are the underwater structures that are made of coral polyps held together by calcium carbonate. Corals are animals.

The soft polyps inside the hard parts of corals are naturally translucent and get their beautiful colour from algae living inside them. They are usually found in shallow areas at a depthof 150 feet. Coral reefs are counterpart to the tropical rain forest in terms of species diversity and biological productivity in the Ocean.

What are coral polyps?


Coral polyps are the individual corals that are found on the calcium carbonate exoskeletons of their ancestors. These polyps have microscopic algae called ‘zooxanthellae’ living within their tissues.

The corals and algae have a mutualistic relationship. The coral provides the zooxanthellae with the compounds necessary for photosynthesis.  In return, the zooxanthellae supply the coral with organic products of photosynthesis, like carbohydrates, which are utilized by the coral polyps for synthesis of their calcium carbonate skeletons.

Where do the coral reefs occur?

Corals are in all the oceans but the biggest coral reefs are mostly found in the clear, shallow waters of the tropics and subtropics. The largest of these coral reef systems, The Great Barrier Reef in Australia, the largest coral reef is more than 1,500 miles long.

coral reefs distribution

Great Barrier Reef

Great Barrier Reef

The Great Barrier Reef is the largest and richest coral reef in the world. It is composed of over 2,900 individual reefs and 900 islands stretching for over 2,300 kilometres over an area of approximately 344,400 square kilometres.

The reef is located in the Coral Sea, off the coast of Queensland, Australia. The entire ecosystem was inscribed as World Heritage in 1981.

Why is it important?

The world’s coral reefs do more for the earth than provide underwater beauty. They occupy just 0.1% of the ocean’s surface but are home to 25% of marine species. Additionally, reefs provide a wide variety of ecosystem services such as subsistence food, protection from flooding and sustaining the fishing and tourism industries.

Coral reefs harbour the highest biodiversity of any ecosystem globally and directly support over 500 million people worldwide, mostly in poor countries.