Into the deep blue

Cameras and curiosity reach above and below the oceans, and bring back many spectacular behaviours of sea-beings in the BBC documentary Blue Planet II. And some of these actions have been filmed for the first time ever, says 91-year-old Sir David Attenborough, the narrator of the seven-part series. He even promises there are creatures 'beyond our imagination' in the depths.

Each episode explores a habitat: kelp forests, corals, coasts, deep waters, etc. So, through beautiful scenes and photography, we learn that somewhere in South Africa, the bottlenose dolphins surf the waves only for pleasure and social bonding; see a tuskfish crack open a clam using a tool in the Great Barrier Reef; gape at a trick a female fish pulls off after a period of growth; quiet down to watch if the clever octopus can trick his predator with a decorated armour; and wonder at the cruelty of giant trevallies (fish) that leap from water to prey on birds learning to fly in the lagoon of an Indian Ocean atoll.

These are small yet mighty glimpses of life that unfold inside the world's largest habitat. The four years of making the documentary include 125 expeditions, 6,000 hours diving underwater, 39 countries, and spells of disappointments.

In a first, the second episode reaches the deepest point in the ocean (almost 11 kilometres from the surface), the Mariana Trench. The environment is harsher with crushing pressure and no light. And yet, fishes with feet, a shrimp love story inside a coral, and bone-eating worms are all lives that thrive there.

There is a strong reminder of city life in coral habitats where varieties of fish swim in strong numbers and bright colours. Some species like green turtles approach coral cities for a dose of cleansing. And some dolphin species make it their playground with corals as their toys.

The most dramatic moments of the series are laced with fantastic background music; other times, natural underwater soundscapes keep the story going.

And the last 10 minutes of every episode accommodate a behind-the-scenes segment called 'Into The Blue'. Here, in complete underwater darkness, a pair of cameramen are seen filming the crazy dance of mobula rays that causes trails of light (a phenomenon called bioluminescence).

When Sir David Attenborough remarks that new science and new technology have allowed them to go deeper into the oceans, he also refers to the many kinds of cameras adopted for the series.

The iconic scene of a mother and baby walrus on an iceberg is captured by a megadome camera, which allows viewers to see both above and below water at once. Or tow cameras, suited to follow the fast movements of dolphins.

As jaw-dropping as the visuals may be, the show makes it a point to address the failing health of the oceans. A protective walrus mother and her baby scouting for space on the ever-melting ice float is caused by the rise in temperatures, says the narrator. Will the walruses find their haven?