Coral Reefs

Coral Reefs

Published: 15 October 2017
Introduction -
An interview with James Honeyborne - Executive Producer
An interview with Mark Brownlow - Series Producer
One Ocean - Episode 1
The Deep - Episode 2
Coral Reefs - Episode 3
Big Blue - Episode 4
Green Seas - Episode 5
Coasts - Episode 6
Our Blue Planet - Episode 7
On location with Blue Planet II -
About the series -
Meet the team -

Coral reefs are home to a quarter of all marine species. Survival in these undersea mega-cities is a challenge with many different solutions.

A turtle heads to the reef's equivalent of a health spa - but she must use trickery to avoid the queue. A remarkable Grouper uses the fish equivalent of sign language to collaborate with an octopus, flushing their prey out of hiding holes.

A metre-long, ferocious-jawed Bobbit Worm hides in its tunnel. Monocle Bream retaliate by squirting water to expose its sandy lair.

Filmed in super macro time-lapse, coral polyps grow and die, laying the foundation for structures we can see from space. Whirlpools, tides and caves create currents.

As darkness falls, sharks gather in their hundreds to take advantage of a Grouper spawning event.

Rising temperatures have led to one of the most devastating coral bleaching event in recorded history. But there is hope. We witness one of the greatest spawning events in the oceans: corals, fish and invertebrates release a snowstorm of eggs during just one night.

Key story - Grouper gesturing and hunting with octopus

Written by Yoland Bosiger, Researcher

Coral Grouper are some of the most common coral reef inhabitants and yet in the last ten years, research shows that their behaviour is so sophisticated that some aspects of their intelligence might rival that of chimpanzees. Groupers are mid water predators feeding on small coral reef fishes. They are fast in the open sea but too large to access prey in cracks and crevices. For this reason they seek out the assistance of a more manoeuvrable marine creature – a reef octopus. But what is truly amazing is that this is not simply a passive partnership - these animals communicate with each other. By assuming the headstand position and shaking their head from side to side above where a little fish is hiding, the grouper is able to tell the octopus where the prey is hidden. Gestures such as this are thought to only occur in the largest brained species and mean that fish are able to think flexibly to achieve their goals. Not only is this behaviour challenging our understanding of what a fish knows but it’s also making scientist rethink the definition of animal intelligence.

Filming locations

1. Bottlenose Dolphins - Egypt
2. Green Turtles, Saddleback Clownfish, Bump Head Parrotfish - Borneo

3. Grouper, Octopus, coral bleaching, various corals - Great Barrier Reef, Australia
4. Broad Club Cuttlefish, Bobbit Worm, Monocle Bream - Indonesia
5. Manta Rays - Maldives
6. Grouper, Grey Reef Sharks - French Polynesia
7. Various corals - Philippines
8. Whirlpool, various reef fish, invertebrates - Bahamas

Key facts

  • Coral reefs cover just 0.1% of the ocean’s surface area, yet they are home to 25% of all known marine species, and new ones are being discovered every day
  • The variety of life supported by coral reefs rivals in many ways, that of the tropical forests of the Amazon or New Guinea
  • Corals are not plants but in fact animals which are closely related to jellyfish and anemones
  • Corals are predators. While many get the majority of their energy from photosynthetic cells living in their tissue, corals also have barbed, venomous stinging cells that catch passing plankton and small fish
  • Corals can live to several thousand years in age - at which point the coral colonies can be as big as a small house.

Crew filming facts:

  • Across four years, the reef team spent 250 days at sea and 1,500 hours underwater diving
  • The reef team’s longest dive was four hours and 20 mins and deepest dive was 40m
  • While filming the team endured El Niño conditions, typhoons, storms and unseasonable flooding

Dolphins sleep and play

Location: Egypt
Species: Bottlenose Dolphins


  • Dolphins have lungs and breathe air like we do. They can hold their breath for more than 10 minutes!
  • Dolphins sleep while they are swimming. However, half of their brain is awake
  • Dolphins can swim at a speed of up to 35 kilometres per hour and can dive to a depth of 300 metres
  • Dolphins in the Red Sea play with seaweed, pieces of coral, jellyfish and other sea creatures

Great Barrier Reef, Australia


  • The Great Barrier Reef is the world's largest living structure. It is made up of around 3,000 coral reefs and is larger in area than the entire United Kingdom
  • The Great Barrier Reef has looked something like it does today, on and off, for over 20 million years
  • This natural icon is so large it can even be seen from outer space
  • The Great Barrier Reef includes 600 types of soft and hard corals, more than 100 species of jellyfish, 3,000 varieties of molluscs, 500 species of worms, 1,625 types of fish, 133 varieties of sharks and rays, and more than 30 species of whales and dolphins


Location: Borneo
Species: Saddleback Clownfish


  • Using their all their strength, they are able to push large objects, sometimes up to 10 times their own weight up to two meters in distance to their anemone - an incredible feat for a tiny fish.
  • Scientific research born from this filming found that these eclectic collectors are highly selective about the objects the push to their nests, preferring nice solid objects with smooth surfaces and colour that blends in with their unborn offspring
  • Many coral reef fish have the ability to change sex but clownfish are one of the few fish to change from male to female. If a dominant female dies, a subordinate male will change sex to become the new dominant female
  • The coral reef team’s longest dive was on the clownfish dive - four hours and 20 minutes spent observing their egg-laying behaviour

Coral Grouper and Octopus

Great Barrier Reef, Australia

Our researcher Yoland Bosiger heard this fantastic story from Dr Alexander Vail who had grown up on a tiny island in the Great Barrier Reef. From observing the reef over the years, he’d found out that the Coral Grouper which is a fish that’s often caught and eaten in Australia, that has revolutionised our thinking about fish.

The Coral Grouper can’t always hunt effectively by himself, because there are so many hiding places all over the reef for the little fish that he eats. What we discovered is that this fish is capable of forward planning and co-operatively hunting with a completely unrelated animal, in this case an Octopus. The Grouper finds the fish and if he can’t get to it in the coral he goes off and does a display to the Octopus; he puts his head down, flashes white, wiggles in front of the Octopus and gets its attention. Then they both come over to where the fish is hiding and if the Octopus wants to play, it can use its tentacles to get in and actually flush the fish out. Once it’s out in the open the Coral Grouper gets the fish about half the time, and about half the time the Octopus snags it.

If we’d have tried to film that sequence a few years ago we’d have ended up filming a lot of it from slightly above. With the underwater probe camera we managed to get inside the reef - and you’re looking in the reef like you’re a little fish with these Octopus tentacles coming down all around you. You really feel like you’re experiencing this behaviour. It’s the only way in a six minute sequence that you can truly understand it and truly come into their world. In the case of the Coral Grouper and the Octopus it’s a new story, new to science since the original Blue Planet was filmed.

Jonathan Smith
Producer, Coral Reefs