What is symbiosis? 

Do you ever feel there is something or someone you could not live without? There is a term for that – Symbiosis – and it is quite common, particularly out on the Reef.

When two organisms of distinct species live together, where at least one of them benefits, this is called a symbiotic relationship.  

Sea anemone and clownfish 

One of the most popular couples on the Reef is the clownfish and the anemone. The anemone is not just a home for the clownfish; it is an animal itself.  

The anemone is a relative of the jellyfish, sharing the same trait of stinging tentacles. It uses these tentacles to sting and catches its prey.

The clownfish avoid becoming dinner by covering itself in the same mucous as the tentacles to let the anemone know it is not prey.

The clownfish can hide inside the anemone without fearing becoming prey for larger fish. Any animal that comes too close will end up as lunch for the anemone.

In return for its protective home, the clownfish will feed its anemone home, bringing food back to its host to eat.  

Alpheid shrimp and gobies 

This unlikely couple complements each other perfectly. The tiny shrimp is known for its strength, which is uncanny for its size. It spends most of its day landscaping and building tunnels – not only for itself but for its housemate, the goby.

As the shrimp has such poor eyesight, the goby plays a vital role as a watchkeeper.

With its long antennae always keeping contact with the goby, the shrimp can detect and react to any sudden movements that the shrimp makes, allowing them both to hide safely within the tunnel. 

Cleaner shrimp and hosts 

One of the most underrated partnerships on the Reef is that of the cleaner shrimp and its host. Setting up stations around the Reef, the shrimp will advertise that it is open for business by swaying.

Like a carwash, other animals will queue to wait for cleaning. The shrimp will crawl all over the fish, including in the mouth, removing dead skin and parasites and even cleaning wounds.

In exchange for this health check, the shrimp receives a free meal. But aren’t the shrimp concerned that they will become a snack? It is an unwritten rule on the Reef that you do not eat these animals.

If these shrimps ended up on the menu, there would be no one left to keep everyone else healthy.  

Remora and other fish 

Not everyone benefits in these relationships. For example, the remora hangs around other larger animals like sharks and turtles – waiting for a free feed.

You may know these fish as sucker fish, using their modified fins to attach themselves to their companions. As the companion animal feeds, the remora will position itself to pick up any of the scraps that may have been missed.

Riding along with someone bigger than you is also a fantastic way to save energy and escape the chance of being a snack for a predator.  

Corals and Zooxanthellae 

Not every relationship is between two animals. One of the hottest topics on the Reef relates to one of the most common relationships on the Reef.

A tiny single celled alga, zooxanthellae, lives within the tissues of coral polyps, the individual animals that make up a coral colony.

The colours recognised worldwide associated with these colonial animals are those of the tiny algae.

The algae live within the tissues of the coral to capture sunlight and convert it to nutrients and oxygen through photosynthesis the same way other plants do.

In return, the algae can use the carbon dioxide the polyps produce to use in its photosynthesis.

It is when a coral becomes stressed that it expels these coloured algae out into the water column leaving its tissues white. This process is called bleaching. 

• Did you know that scientists monitor the duration and distribution of coral bleaching as an indicator of the Great Barrier Reef’s health?
• You can find out more about Reef Health via our weekly updates.