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Sir David Attenborough explores the dangerous frontiers created by the world's coasts, where animals fight for survival amidst constant change.

On South Africa’s Robberg Peninsula, thousands of Cape fur seals are squeezed onto a small ledge. A yearling pup escapes into the water, where the clumsy youngster becomes nimble and graceful. In recent years, this coast has been home to unprecedented numbers of great white sharks, and the seal colony must band together if they’re to see off the world’s most notorious predator.

The Arctic coast is the scene of the biggest seasonal transformation on earth, and the melting of billions of tonnes of ice brings short-lived opportunities to these coastal waters. Animals arrive en masse, perhaps the strangest of which is the sea angel. This beguiling creature has a devilish side – it’s a voracious predator whose ambush wouldn’t be amiss in a sci-fi horror.

On Namibia’s infamous Skeleton Coast, where the world’s oldest desert meets the cold Atlantic, we meet some unexpected residents. Hungry lions discover this coast for the first time in 40 years and try their luck in a huge seabird colony.

Coasts attract visitors from far afield. A southern right whale reaches her journey’s end at Peninsula Valdes, Argentina. In British Columbia, terrestrial garter snakes take the plunge into chilly waters in search of a meal.

In tropical Raja Ampat, Indonesia, coral reef is sheltered by forest. Mangrove trees are salt-tolerant and rooted in the seabed, providing a unique opportunity for archer fish, which use jets of water like arrows to shoot down insects from high above.

By contrast, the shallow lagoons of Mexico’s Yucatan are very exposed. It’s here in these hostile, hypersaline pools that Caribbean flamingos choose to nest, but can their offspring survive the tropical storms that have arrived early?

Coasts are the front line in our changing world. Increasingly unpredictable storms and sea level rises are urgent threats to those that make their homes near the coast, including nearly 40% of the world’s human population.

On tiny Raine Island, tens of thousands of female green turtles come ashore to nest, but many are stranded by the ebbing tide. The island is on borrowed time. This, the world’s largest green turtle rookery, is set to disappear beneath the waves. The end of the episode reveals the speed of change over the course of Sir David's lifetime. His was the first filming expedition in 1957. Little could he have known just how much the island would change in 66 years.