Great Barrier Reef

Sometimes when we consider habitats we forget about the biggest habitat on the planet... the ocean! There are so many different animals that live in the ocean, from mammals to fish to reptiles. I feel like most humans spend very little time actually in the water, so we tend to forget that there is an entire world below sea-level. The Great Barrier Reef is a very famous habitat under the sea; we have included some neat facts about the natural wonder below.

[Location]   [Structure]   [Water Environment]   [Marine Plants]   [Marine Animals]   [Threats]


The Great Barrier Reef is located just off the coast of Queensland, Australia. It is actually a system of separate reefs that can all be found in the Coral Sea and as a whole make up the large habitat. The Great Barrier Reef has a collection of approximately 2900 individual reefs and 900 islands.


Map of the Great Barrier Reef


The Great Barrier Reef is the largest reef system in the world; so big it can be seen from space! It spreads across the floor of the Coal Sea for approximately 2600km (or 1616 miles). At some points along the Australian Coast the reef is 65km wide. The Great Barrier Reef lies close to the shore in some locations (the closest being 15 km away from shore), while other sections may not begin until as far as 150km away from shore!



Marine animal hiding in coral polyps
Jean Wimmerlin on Unsplash
A marine animal hiding amongst coral polyps
Coral reefs are very complex structures that form over millions of years and grow very slowly. They are made up of layers of limestone (calcium carbonate). Despite their large appearance, coral reefs must start somewhere and this is how they grow:

Due to the way that coral reefs form many people consider the Great Barrier Reef to be the largest structure built by living creatures. Although, this is not entirely true because the Great Barrier Reef is not one giant reef but a collection of thousands of individual reefs.

There are three different kinds of reefs:


Water Environment:
The waters around the Great Barrier Reef are from the Pacific Ocean. It tends to remain at a consistent temperature all year round, and is very warm, ranging between 21°C and 38°C. The water is remarkably clear, which makes it a prime destination to explore the coral reefs. The water remains clear enough to see the underwater environment without disruption from floating sediment until a depth of about 30 meters.


Marine Plants:
There are not many different plants that grow around the Great Barrier Reef because the underwater habitat makes it difficult for most plants to thrive. The plants that do grow along the collection of coral reefs are different types of algae (like seaweed), sea grasses, sea lettuce, etc.

Ocean Algae on a Coral Reef
Linus Nylund on Unsplash

One of the most important plants in the Great Barrier Reef is a type of algae called crustose coralline algae. It forms a symbiotic relationship with coral. The algae helps the coral reef grow by releasing a sediment that acts as a sort of glue to hold together the layers of limestone.

Another very important species of plant to the Great Barrier Reef are mangrove plants. Although they do not live underneath the surface of the water completely, mangrove plants grow along the shores near the Great Barrier Reef and help stabalize the shoreline. There roots are also very important because they filter the waters around the coral reefs by removing the pollutants. There are around 80 different species of mangrove around the world, half of which are present along the coastline of Australia.

Mangroves on the Shoreline
David Unger, flickr creative commons, CC BY-NC-ND 2.0


Marine Animals:
While not many different plants can grow underneath the waters around the Great Barrier Reef, there are a surprising number of animals that call the reef home. From fish and sharks to reptiles and crustaceons, the Great Barrier Reef is a bustling community!

Coral Reef
Milos Prelevic on Unsplash

We have already spoken about the importance of coral to the Great Barrier Reef in our section about the reef's structure. Although coral looks more like a rock or plant than an animal and cannot travel freely in its habitat, it is actually an animal. Each individual organism (coral polyp) is really small—averaging at about 1.5 centimeters in diameter. There are also many different types of coral, ranging from soft coral to hard coral.

The Great Barrier Reef is home to over 1500 different kinds of fish! That is a lot of colorful creatures. To name only a few, there are clownfish (like Nemo), lionfish, parrot fish, and stonefish (rather large fish that camouflage themselves like rocks). Aside from classic fish the Great Barrier Reef is also home to plenty of shellfish like giant clams, peacock mantis shrimp, and boxer crabs.

Among the other marine animals you may find squid and octopus (like the blue-ringed octopus or cuttlefish), reptiles like sea turtles, or different species of whales and sharks.

When we hear “dangerous marine animal”; our brains usually think of sharks straight away, but what about some of the smaller animals? Animals like sea snakes, sea urchines, sting rays, jellyfish, and sea slugs can be very dangerous because they defend themselves with poisonous and painful stings.

Great Barrier Reef
Sam Soffes on Unsplash

In the Great Barrier Reef there is a particularily cute and goofy looking marine animal called the duogong. They are rather large animals that feed on underwater plants like algae, sea grasses, and seaweeds. Historically, sailors were known to mistake duogongs that they saw swimming underneath the water for mermaids!


Environmental & Human Threats:
One of the signs that a coral reef is being threatened is coral bleaching, which is when coral is whitened. Coral bleaching occurs when the algae that sustains a symbiotic relationship with the coral dies out. This can be caused by a number of different things, some of which are listed below.

Great Barrier Reef
Catrin Johnson on Unsplash

If coral is without its algae counterpart for a long period of time it may cause individual coral polyps to die or even the entire reef to die. Unfortunately since coral reefs are home to so many marine animals and plants, the loss of habitat would affect many species.

Ocean Acidity – Limestone is the building block of coral reefs and a very basic substance, so when it dissolves slowly it lowers the acidity of the water around a coral reef. With the rising acidity of the world's oceans more limestone is dissolving to help keep the pH levels of the oceans balanced. This leads to the coral reefs being damaged and is one of the environmental threats to the health of the Great Barrier Reef.

Crown of Thorns Starfish
Johan J.Ingles-Le Nobel, flickr creative commons, CC BY-ND 2.0

Crown-of-Thorns Starfish – This particular species of starfish is an invasive species in the Great Barrier Reef and can cause a lot of damage because it feasts on coral polyps. Originally the starfish was not invasive, but in the 20th century the predators (eg. Pacific Triton) of the starfish were overhunted. Without any predators to keep the population of the crown-of-thorns starfish under control, the starfish became a threat to the coral reefs.

Rising Ocean Temperatures – Due to climate change the ocean temperatures are rising, especially surface water temperatures like those surrounding the Great Barrier Reef. Unfortunately even small shifts in temperature can cause coral bleaching. Rising ocean temperatures are considered one of the greatest threats to the Great Barrier Reef because of the extreme nature of climate change.

Tourism – After all we have learned it is hard to deny that the Great Barrier Reef is amazing, which is why so many people choose to explore the reef each year! The amount of tourists that visit each year is approximately 2 million. While this is a great way to boost economy and educate people on the natural wonders of the coral reef, it can be detrimental to the health of the reef if tourism is not carefully monitored. Controls must be in plae to prevent humans from walking on the coral, breaking off pieces of the reef as souvenirs, dropping anchors on the reefs and grounding boats on them, and dragging scuba gear across the coral.




“About The Reef | What Is The Great Barrier Reef?” Great Barrier Reef,,
“Great Barrier Reef (Animals, Plants, Coral)What Is the Great Barrier Reef?” Great Barrier Reef - Animals - Plants - Attractions - Things to Do,
“Great Barrier Reef Facts for Kids - Pictures & Information.” Science Kids - Fun Science & Technology for Kids!, Science Kids, 8 July 2016,
“How Are Coral Reefs Formed?” Aquaworld, 1 June 2015,
Johnson, Maggie D. “Coralline Algae: The Unsung Architects of Coral Reefs.” Ocean Portal | Smithsonian, Smithsonian's National Museum of Natural History, 21 Dec. 2017,
The Editors of Encyclopaedia Britannica. “Great Barrier Reef.” Encyclopaedia Britannica, Encyclopaedia Britannica, Inc., 16 Mar. 2018,
US Department of Commerce. “Corals.” NOAA National Ocean Service Education: Corals, US Department of Commerce, 6 July 2017,
US Department of Commerce. “What Is a Coral Reef Made of?” NOAA's National Ocean Service, 1 June 2013,


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