´óÏó´«Ã½

Marine invertebrates are extraordinarily diverse, outnumbering fish by ten to one. They range from some of the most primitive creatures in the sea to some of the most intelligent.

Many creatures of the deep make a nightly migration to shallower water.

For the first time, a huge number of six-foot long carnivorous Humboldt squid are filmed hunting co-operatively to attack a shoal of fish off the coast of Mexico. Co-ordinating their assault, they herd the fish and drive them onto the reef. They flash their bodies red and white – either to confuse the fish or to signal to each other when they are about to go in for an attack.

Conditions under the ice in Antarctica's Ross Sea are similar to the deep ocean. But, rather surprisingly, the sea bed is carpeted with thousands of sea stars, sea urchins and huge nemertean worms which make this sub-zero world their home. Seen in tracking time lapse for the first time, they swarm across the sea bed to feed on a dead seal pup carcass – a rare bounty.

Off the southern coast of Australia giant spider crabs emerge from the deep to congregate in vast numbers in the shallows to moult. Having shed their old shells, they are soft-bodied for a while before their new shell hardens. This is their opportunity to mate, but it is also a time when they are vulnerable to attack from stingrays.

Giant Australian cuttlefish also emerge from deep water to mate in the shallows. A large male will attract and mate with a female, and then guard her from his rivals. If another large male challenges him, he flashes colours and stripes that pulse along his side to tell the rival to keep off. However, devious smaller males have a different approach. They change their colour to look like a female and hold their tentacles just like a female who wants to mate. With this disguise, they slowly swim towards the female, and right under the larger male's nose, quickly mate with her!

The female Pacific giant octopus is a dedicated parent – she finds a cave and blocks herself and her eggs in with rocks. For the next six months she does not leave her den but guards her eggs, keeping them oxygenated and free from disease and predators. Gradually she starves, and her last act of devotion is blowing water over her eggs to help them hatch. And then she dies.

In the warm but nutrient-poor seas of the tropics, microscopic coral polyps multiply and grow, creating the largest living structures in the world that, staggeringly, harbour a quarter of all marine life. And yet coral reefs are built by the tiniest of creatures, occupying less than half of one per cent of the oceans' floor.

Sink Or Swim

The Life team travelled to the freezing waters of the Antarctic to film the slow motion world of the creatures living under the ice.

First they drilled a huge hole in the ice to feed all the equipment through. It took more than 150 dives to gradually construct and operate a tracking time lapse rig.

And, finally, they could film the behaviour of starfish, sea urchins and giant worms swarming over a dead seal pup, speeded up 500 times.

The Life team also discovered creating their very own ship wreck in the Bahamas was much more difficult than they imagined – but in the end the boat sank perfectly, settling upright on the bottom. The team returned several times during the next two years to watch nature take a hold on the rusting hulk.

Producer: Neil Lucas.