Chapter One

The Perfect Reef


The Great Barrier Reef stretches 2,300 kilometers down the eastern coast of Australia. Covering an incredible 344,400 square kilometers, an area the size of Italy, it is more than twice the size of the next largest coral reef. With over 1500 species of fish, 600 coral species and 30 different whale and dolphin species, it is one of the most biodiverse and complex ecosystems on the planet. In this chapter, we'll investigate what it is that makes The Great Barrier Reef such a special place, how far some animals are prepared to travel to get here, and some of the surprising ways animals navigate their way through this beautiful world.

How does Coral Grow?

There are over 600 species of hard coral on the Great Barrier Reef. All hard corals build their limestone homes by harvesting calcium carbonate from the ocean around them. To see this in action, you must speed up time.

Those humble reef builders - coral polyps - lay the foundations for an ecosystem so diverse, it supports a dazzling range of marine creatures, from tiny plankton to huge whales. But there is one animal living here with an ability shared by no other creature on the planet…

The Mantis Shrimp

They have the most complex visual system in the animal kingdom. While humans have just three types of light detecting cells, mantis shrimps can have up to sixteen. They use their ability to target their prey with devastating accuracy, delivering a deadly punch that accelerates faster than a .22 calibre bullet. So what might the world look like if we could see like the Mantis Shrimp?

Launch Mantis Vision

A Ministry of Sound

Reefs aren't as quiet as you might expect. They emit a cacophony of different sounds, from mating calls to the mechanical crunching of fish feasting on stony coral. Like humans, fish use this sound to make sense of their environment.

Have a listen

Finding home — the Clown Fish story


The Great Barrier Reef is one of the most crowded ecosystems on the planet, survival here takes great innovation and sometimes, collaboration. To get on in this competitive world, Clownfish have formed a special symbiotic relationship with a surprising animal; a sea anemone. For the clownfish and the anemone, cooperation is the key to their success.

Most fish avoid anemones. Their harmless looking tentacles are actually packed with stinging cells called nematocysts that will inject a painful toxin into any creature that ventures too close. But a protective layer of mucus gives the Clownfish immunity to the toxins. They can then live within this venomous haven, safe from predators. By way of payment, the clown fish eat the anemone's parasites and scraps of leftover food, keeping it clean and healthy in the process.

It's under the protective shield of these venomous tentacles that a female Clownfish really benefits from this partnership; she lays up to a thousand eggs on the rocks beneath her anemone home! After only a week inside the safety of their egg cases, the young are ready to emerge. They hatch only at night, and once the little larvae are set free they're on their own, spending the first weeks of their life developing in the open ocean before embarking on an epic journey to return home.

But after drifting so far out to sea, how do the young clownfish find their way home?

It's the sound. All that noise on the reef is useful to the Clownfish trying to find their way back to the reef from the open ocean. Fish and invertebrates produce a unique soundscape of clicks, snaps and grunts simply by carrying out their daily duties. Where there is less biodiversity there are fewer clicks and chirps echoing from the reef, its sound is much quieter.

Clownfish, who always start out their lives as males, use these different sounds to their advantage; to find a new home from the open ocean they homes in on the healthier sounds and avoids reefs that sound like they contain too many natural predators. Clownfish rely on this sound to find their way back to the reef after spending their first few weeks out in the open ocean.

Finding a healthy sounding reef is one thing, but there's another obstacle for Clownfish — climate change. New studies suggest that ocean acidification could be affecting the delicate calcium carbonate structure inside the inner ears of Clownfish, making it harder for them to hear or identify healthy reefs, making it even more difficult to for nemo to find his way home.

New studies are also looking into the effects of Ocean Acidification on Clown Fish navigation as new evidence suggests this might be affecting the delicate calcium carbonate structure within the inner ear, making it even more difficult for Clown Fish to find their way home.

We're finding that changes in ocean chemistry are having surprising and worrying affects on the sensory abilities and behaviour of these iconic animals.

Dr. Steve Simpson, Marine Biologist

By ensuring reefs are healthy this will support the rich diversity that gives the Clown Fish the rich soundscape it needs to locate the Reef and by reducing CO2 emissions and reversing the effects of Ocean Acidification, their delicate inner ears can still help it navigate we can ensure that the Clown Fish can find their way home.

Which way home?

The sound of the reef guides young clownfish back from the ocean, to the comfort of their reef homes.

Unhealthy Healthy REEF

For clownfish, their first journey back to the reef is the adventure of a lifetime, but it is dwarfed by the lengths some creatures are prepared to go in order to reach this wonder of the natural world.

A Global Destination

The Great Barrier Reef is a magnet for thousands of animals. Some travel from as far as the freezing sub Antarctic, others come from the tropical Pacific Ocean. In this section we'll look at some of these epic migrations and find out why they travel so far to reach the reef.

Start your journey

David Attenborough's Great Barrier Reef ©Atlantic Productions 2015

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