How Coral Reefs Are Formed - A Beginners Guide

Coral reefs have the highest biodiversity of any ecosystem on the planet. They occupy less than 1% of the ocean floor, yet they are home to more than 25% of marine life. But where did our coral reefs come from? In this blog, we’ll explore how coral reefs are formed, the different types of coral reefs, and at the end we’ll share some of the work we’re doing in restoring Australia’s coral reefs with the support of people like you.  

Let’s get to it! 

How are coral reefs formed? 

Coral reefs are formed when coral larvae attach to submerged rocks or other hard surfaces along the edges of islands or continents. As the corals grow and multiply, expanding in size and covering more surface area, coral reefs are formed. Reef-building corals are a specific type of coral, known as ‘hard’ corals - they’re the ones you’ll see most of the time when snorkelling or diving around a coral reef. On the other hand there are soft corals, which you’ve also probably spotted, such as sea fans and sea fingers, which are more flexible organisms that can resemble trees and look soft in appearance.  

 In order for coral reefs to form and thrive, they need warm salty water (around 21-29° C) and that water also needs to be clear and relatively shallow. With these conditions in abundance in places like the west northern coast of Australia, corals can absorb sunlight and turn it into food using their symbiotic algae known as zooxanthellae. In saying this, corals have also been found at depths of up to 300 feet.   

With the help of science we now know that most established coral reefs that we enjoy today have been around for approximately 5,000-10,000 years. That’s quite a long time! From looking deeper into the geological record we also know that the ancestors of modern coral reef ecosystems were formed around 240 million years ago.  

What are the different types of coral reefs? 

There are four different types of coral reefs that you should know about. Let’s take a look at the four types and what makes them each so special.  

Fringing Reefs

Fringing reefs typically grow near the coastline, tightly weaved around islands and continents. They are separated from the shore by narrow lagoons and are the most common type of coral reef out there. 

Barrier Reefs 

Barrier reefs are, as you can probably guess, coral reefs that are long and formed in a way that is parallel to the coastline. They are separated by deeper and wider lagoons than their Fringing Reef counterparts, but at their shallowest parts the corals can appear above water’s surface forming a literal ‘barrier’. The world’s most famous barrier reef is the Great Barrier Reef, right here in Australia. It’s also the reef that we spend our time conserving and restoring.   

Patch Reefs 

Patch reefs are small, isolated patches of coral reefs that are formed on the bottom of an island platform or continental shelf. They usually occur between fringing reefs and barrier reefs and are a welcome partner in the marine ecosystem. These reefs vary in size, with some being vast and large and others small, and you’ll probably only see these reefs when diving. 


Picture this - a ring of coral in a beautiful, picturesque lagoon. That’s what an Atoll is, and they’re usually formed when islands surrounded by fringing reefs sink into the sea or when the sea level rises around the island, causing it to submerge. These islands that go below the waves to form the base of atolls are most often the top of underwater volcanoes, and the result is quite a beautiful sight if you ask us. 

How we are restoring coral reefs in Australia 

Australia’s Great Barrier Reef is a precious natural resource and ecosystem, made up of 2,900 individual reefs. The reef covers a surface area larger than Italy, and is well-known as the largest coral reef in the world.  

Unfortunately, due to changes in our environment, the Great Barrier Reef has experienced significant coral bleaching events. In 2016 and 2017 there were unprecedented back-to-back coral bleaching events which affected almost third of the Great Barrier Reef. 

We knew something had to be done, so the Reef Restoration Foundation was formed and we began our work by establishing the first ocean-based coral nursery to regenerate coral reefs from the Great Barrier Reef at Fitzroy Island, near Cairns. This project, which you can learn more about here, was successful and it’s led us to where we are today, continuing to expand our coral nurseries through the help of generous donations from people like you and corporate donors.  

Our restoration methods and efforts will accelerate recovery from the recent coral bleaching events and enable this historic natural ecosystem to better withstand future climate impacts. If you want to be part of this initiative and strengthen this critically important ecosystem, donate here or find out more about volunteering with the Reef Restoration Foundation.  

We hope you found this article on how coral reefs are formed interesting and useful. If you’d like to learn more about corals and see awesome photos of the work our volunteers are doing, follow us on Instagram 

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