Tropical Seas

The warm, sunlit waters of the tropics support the greatest diversity of life in the ocean. Bathed in year-round sunlight for millions of years, these seas are home to more species than anywhere else on earth. In a world where competition is fierce, animals have evolved extraordinary ways to survive. Yet even in these seemingly familiar waters, remarkable new behaviours are still being discovered.

At the northern tip of Australia, a tawny nurse shark patrols the shallows in search of food. Too slow to chase fish in open water, it relies on a surprising strategy. Gathering in groups, the sharks appear to work together in a coordinated ambush. After waiting patiently in the shallows, they drive huge shoals of fish out of the water and onto the beach before vacuuming up their prey by the mouthful.

Further west, Shark Bay is home to one of the world's greatest concentrations of dolphins. Here, bottlenose dolphins have developed a hunting technique previously unknown to science. Carrying sea sponges to isolated coral bommies, they use them to block the hiding places of fish, creating one of the most sophisticated examples of trap-setting ever documented in the animal kingdom.

Across the tropics, coral reefs are bustling underwater cities where predators and prey are locked in a constant battle. In the Red Sea, coral groupers communicate with two very different hunting partners - giant Maori wrasse and sleek moray eels. Only by working together can they flush prey from the reef's maze of crevices, making the grouper far more successful than it could ever be alone. After dark in Bali, the reefs take a more sinister turn as harlequin shrimp stalk starfish for supper. Barely five centimetres long, these tiny hunters have developed a macabre way of overcoming prey many times their size.

Beyond the reefs lie immense plains of sand and mud. Here, humpback whales arrive after epic migrations from Antarctica. For one female, this will be her final journey. As she takes her last breath, hundreds of sharks gather nearby. In death, her body becomes a vital source of nutrients, feeding a host of scavengers and bringing life to one of the tropical seas' most barren landscapes.

Far out to sea lies Fernando de Noronha, a remote volcanic island in the equatorial Atlantic. Here, hundreds of green turtles gather to graze on lush seaweed. Their abundance attracts one of the tropics' most formidable predators: the tiger shark. Yet turtles are far from defenceless, combining surprising agility with nature's most effective armour.

In the seagrass meadows, dugongs spend up to ten hours a day grazing, cultivating an unexpected following. Remoras hitch a ride and feed on parasites, dead skin and even the nutrient-rich waste left in their wake.

Among tangled mangrove roots, one of the planet's most effective carbon-storing habitats, male fiddler crabs risk their lives for a chance to mate, dodging the probing bills of hungry scarlet ibis before the tide returns.

There are some special places on earth where all these tropical habitats converge, like in the Coral Triangle of Asia. Here, a clownfish family depends on a single sea anemone for survival. When an unprecedented marine heatwave causes both corals and anemones to bleach, the fish fight to save their home. By cleaning away debris and helping oxygenate their host, they do everything they can to keep it alive until cooler waters return.

But the tropical seas are changing. Across the tropics, many reefs are struggling to recover from increasingly frequent marine heatwaves. As scientists race to understand and protect these extraordinary ecosystems, the tropical seas remain a world of ingenuity and wonder, where every habitat reveals a new and surprising story of survival.