The Great Barrier Reef is the most extensive coral reef collection on Earth.

The coral reef ecosystem of Australia’s Great Barrier Reef is a mesmerising underwater wonderland teeming with life and colour. Stretching over 2,300 kilometres along the Queensland coast, this UNESCO World Heritage site is home to the most extensive coral reef system. Under the crystal-clear waters, vibrant coral formations create intricate landscapes that shelter and sustain various marine species. From tiny clownfish darting among the coral branches to majestic humpback whales gliding through the depths, the Great Barrier Reef offers an unparalleled opportunity to witness the beauty and diversity of the underwater world. With its kaleidoscope of colours, bustling marine habitats, and breathtaking natural beauty, exploring the coral reef is an unforgettable experience for visitors of all ages.

 

Coral Reef

Are corals animals or plants?

To form the most remarkable structures of biological origin on the planet, coral relies on its close association with algae.

In the same way that most plants “take root,” corals attach themselves to the ocean floor.  In contrast to most other creatures, we cannot identify them based on their faces or other distinguishing features.

Don’t miss the spectacular annual Great Barrier Reef Coral Spawning Event!

The Great Barrier Reef hosts a breathtaking natural phenomenon: coral spawning every year. This mesmerising event is a must-see for anyone visiting Australia. Click the link to read why you should plan your trip to witness this wonder of nature.

What are corals?

Symbiosis, the scientific term for the relationship between corals and other marine organisms, dates back thousands of years.

Coral reefs use their small, tentacle-like arms to scoop food from the water and bring it into their mouths for digestion. Each soft-bodied polyp secretes a limestone exterior skeleton, most of them being no thicker than a five-cent coin.

Unlike plants, corals do not produce nourishment, making them animals.

Polyps, microscopic coral animals, make up most of the “coral” structures.

This skeleton is attached to the rock or the dead polyp skeletons.
Polyp aggregates found in stony or hard corals reproduce indefinitely, build the limestone basis for coral reefs, and give shape to the known corals that inhabit them.

Many coral colonies can live for an extended period because of this growth, death, and regeneration cycle among individual polyps.

It is common for corals to have plant-like organisms called zooxanthellae.  The microscopic algae are well-protected within the coral tissues and use the metabolic waste products of the coral for photosynthesis, the process by which plants produce their food.

By producing oxygen and removing waste through photosynthesis, algae also provide the corals with the organic compounds they need to grow, survive, and build up a reef.

For over 25 million years, tiny ocean animals and plants have worked symbiotically harmoniously to build the world’s most significant living structure, the coral reef.

What are coral reefs?

When critters live on a coral reef, they create their habitats.

Polyps, the smallest coral organisms, reside in massive clusters called colonies.

Coral reefs can grow for thousands of years, forming reefs up to more than 2,000 kilometres in length.

They are vibrant, diverse ecosystems teeming with various organisms.

The structures they leave behind after death enrich the coral reef.

Coral reefs also support land-based creatures and plants.

Plants take root in shallow water in the mud and sand around a reef.  This area is home to mangrove plants and seagrasses.

Crabs and other small animals can hide in the hollow crevices around the mangrove roots.  In search of food, long-legged birds also wade through mud and water.

According to current estimates, coral reefs have existed for at least 230 million years.

Among the world’s oldest ecosystems, coral reefs, which have been there for a long time, appear to have remained unchanged.

Soft tree corals thrive in the warm waters surrounding mangrove roots.

How many types of coral are there?

The Great Barrier Reef is home to approximately 600 species of coral.  Coral has two main types: complex and soft.

 Hard Coral

Hard coral, also known as stony coral, forms the backbone of coral reefs.  It belongs to the phylum Cnidaria, which includes jellyfish and sea anemones.  Hard coral is so named because it builds a complex, calcium carbonate exoskeleton that supports and protects the coral polyps that live within.

Complex coral colonies can vary in shape, size, and colour depending on the species. Some species form branching structures, while others form massive structures or columns. Hard coral can also come in various colours: brown, green, yellow, and purple.

Hard coral is essential to marine ecosystems, providing habitat for much aquatic life, including fish, crustaceans, and other invertebrates.  Coral reefs, primarily made up of hard coral, are among Earth’s most biologically diverse ecosystems.  They provide valuable services, including protecting coastlines from storms and erosion and supporting commercial and subsistence fisheries.

However, several factors, such as ocean acidification, overfishing, destructive fishing methods, and climate change, threaten hard coral and coral reefs.  These threats can cause coral bleaching, leading to the death of coral colonies and the degradation of coral Reef ecosystems.

Conservation efforts

including coral reef restoration and protection, are crucial for ensuring the survival of hard coral and the health of coral reef ecosystems.

Complex coral polyps are responsible for creating hard coral reefs.  To protect themselves, they employ calcium carbonate to build sturdy structures.

Soft Corals

Gorgonean coral

It is not uncommon for soft corals to coexist peacefully with their stony cousins.
Corals in vibrant gardens can take on the form of shrubs, trees, or even mushrooms.  The type of polyp that dwells inside the coral and its location on the reef determine its shape.

Soft or octocorals differ from hard corals because they lack a hard, calcium-carbonate exoskeleton. Instead, they have a smooth, flexible body of tiny polyps connected by a fleshy tissue called coenenchyme. Soft corals are found in tropical and subtropical waters and are often brightly coloured, with red, pink, orange, and yellow hues.

Soft corals come in various shapes and sizes, including tree-like structures, fans, and whips.  They are also often covered in tiny, hair-like projections called cilia, which help to trap food particles and transport them to the coral polyps.

Like hard coral, soft coral is essential to marine ecosystems. It provides a habitat for many marine life, including fish, crustaceans, and other invertebrates. Soft corals are also an indispensable source of secondary metabolites, which are used in the development of medicines, cosmetics, and other products.

Climate change, ocean acidification, overfishing, and destructive fishing practices threaten soft coral.

Conservation efforts

Coral Reef restoration and protection are crucial for soft corals’ survival and coral reef ecosystems’ health.

Explore our day tours

Stay on the Great Barrier Reef