How Are Coral Reefs Formed?

Have you ever wondered how are coral reefs formed? Coral reef formation is a unique natural phenomenon. It is a diverse ecosystem formed under tropical waters and gives scuba divers and snorkelers a paradise to explore.

The bio-diversity of a coral reef is often called the rainforest of the sea. The coral reefs are home to almost one-fourth of the total species living in the sea. Reefs are mostly found near to coast line in the tropics, but deep sea coral reefs can also be found.

The formation of a Coral Reef

Fringing reefs, the first stage

The first stage of the formation of a coral reef is the coral larvae attaching themselves to rocks or soil near the coasts. The coasts may be of an island or a continent. The larvae become polyps and excrete calcium carbonate, which forms their exoskeleton.

The polyps live only in those waters which have enough sunlight seeping though. They have a symbiotic relation with the microscopic algae Zooxanthellae, which helps them grow. As they grow, they secrete more calcium carbonate.

The secreted calcium carbonate sediments on the rocks and provides a substrate for more polyps coming to attach themselves to the formation. As more and more polyps attach to the substrate, a coral reef is formed.

Calcareous Algae also add their sediments to the structure. The marine animals and plants also add their own remains to the reef as they die and sink. It strengthens the reef and now it can withstand any storm.

The reefs that are initially formed near the coast are known as fringing reefs. Over a period the calcium carbonate converts into lime stone due to pressure.

Barrier Reef – Like our Mesoamerican reef

The fringing reefs slowly combine with each other and form a border line along the coast. The calcium carbonate structures attract more polyps and the spaces are filled up.

It forms a line along the coast and a ring around an island. They create beautiful and colorful formations under water. The sunlight coming through helps them grow together. The Great Barrier Reef found on Australian coast is the biggest continuous reef structure in the world, followed by our own Mesoamerican Reef.


As the coral grows further, it becomes heavy and pushes the sea rocks underneath and then emerge as one more island. More animals are found in an atoll than in the earlier stages. Over a million species can live in one square kilometer coral reef.

The Biodiversity inside a coral reef

A coral reef is a complex ecosystem with varied marine life. They even protect the mangrove and the sea grass from high tides. Algae, fish, echinoderms and many other species depend on the reef for their habitat and food too. The number of species is directly proportional to the mass of the coral reef.

Some vital marine life found in coral reefs


Sponges are critical for the functioning of the coral reef’s ecosystem. They act as filtering agent for the sediments. They convert larger globules into smaller particles, which are then easily absorbed by the reef.


Coral reefs are a paradise for fish. More than 5,000 species of fish live in the coral reefs and we don’t have to explain how important fish are for the food chain. Most fish adapt to the ecosystem and develop camouflage in sync with the corals.


There are many species of invertebrates living in the corals. Sea urchinsslugs and sea anemones are the major types of invertebrates. The star fish are very common in reefs and a marvel to watch during snorkeling or diving tours. Other species like sea snakes and sea birds are also inhabitants of the reefs.

The coral reefs are a tourist’s delight and have great variety of marine species. The reef take thousands of years to grow and are very delicate so they must be protected.
At Aquaworld we have special and guided tours to different reefs so that you can have a wonderful natural experience.