SUNDAY 12 NOVEMBER 2017
BBC One/RTE One
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.