Exclusive Footage: Male Seahorse Gives Birth to 400 Babies

Australia, the Great South Land. Her southern seas hold some of the world's most exotic creatures. Bizarre dragons, living treasure, and camouflaged predators. Here, males give birth at night and wrestle for females by day. It's a playground for some, a hunting ground for others. Isolated from the rest of the planet for 40 million years, the South Coast still holds secrets in its deep, cold waters. Australia's southern coast stretches thousands of miles. Here, the mighty East Australian Current collides with cold eddies from the Tasman Sea. The surf pummels and reshapes the shoreline. Near the center of the South Australian coast sits the town of Waiala on False Bay. On the eastern end of the bay, the peninsula of Point Lowly. These waters are the breeding grounds for giant cuttlefish. Each year from May to August, hundreds of thousands come to mate. Some travel more than a hundred miles. There's no other gathering of cuttlefish like this on the planet. Why they travel only here to breed is a mystery. Weighing more than 13 pounds, these are the world's largest cuttlefish. Cuttlefish live just two years. This annual gathering may be their only chance to mate. With time pressing, males compete for the smaller females. Their bodies pulse with color to intimidate rivals. Special skin cells called chromatophores allow them to change color faster than any other animal. When color fails, fights erupt, but they're seldom fatal. With several males vying for one female, the competition heats up. This male has to tackle two jobs at once, court a female, and fend off interlopers. For all his work, it's the female who chooses her mate. She rejects more than 70% of her suitors. Big males use their size to keep others away from the female. This small male uses a clever tactic to get close to her. He poses as a female by mimicking her color and posture. When the larger males are distracted, he makes his move. Once he wins her affections, the couple intertwines to seal the bond. He deposits his sperm quickly before being noticed. Hundreds of offspring will hatch in a few months from an embrace lasting less than a minute. It's Mother Nature's ultimate kiss. At the end of the mating season, giant cuttlefish leave Spencer Gulf and head out into deeper, colder water. More than 650 miles southeast of Wayala lies Australia's southernmost frontier, Tasmania. It covers almost 27,000 square miles and nearly 40% is a national park. Like living art, vibrant schools of matto fish paint the ocean. Matto have a sensory system called the lateral line running from gills to tail. It's sensitive to the slightest vibration and keeps the school synchronized. As they move around the island, they encounter some of Tasmania's volatile seas. Waves and currents shape all life beneath the surface, especially plants. These bull kelp fronds sway in the surge. The plant grips the rocks with a root-like hold. Leather kelp covers every surface as far down as 80 feet. But for power and grandeur, nothing rivals the giant kelp forest. Kelp forests form some of the most biologically productive ecosystems on Earth. They support thousands of plant and animal species. Gliding through an undersea jungle is a creature from a fairy tale, the weedy sea dragon found only in Australia's southern waters. Despite its fierce name, the sea dragon is a gentle dwarf. It grows no more than 18 inches long. Propelled by tiny clear fins, it seems to drift like a weed. Its neon colors mimic the algae and sponges, and its leafy skin flaps mirror kelp fronds. Why the sea dragon needs such heavy camouflage is an enigma. It seems to have few predators. Climate change, over-harvesting and pollution, the true threats to the dragon, have destroyed 95% of Australia's giant kelp forests. The weedy sea dragon is now listed as a threatened species, along with others that share the forests. In the shadow of giant kelp lives a cousin of the sea dragon, the seahorse, one of Tasmania's most iconic residents. Swaying in the surge, this big-bellied seahorse has a bigger belly than usual. Cued by lunar cycles, it prepares to give birth. But the one to deliver the new generation isn't the female. In an extraordinary twist of nature, all males have a brood pouch in their bellies. After the female deposits her eggs in the male's pouch, he fertilizes them. During the pregnancy, the couple engages in courtship dances. Almost a month later, in the dead of night, he goes into labor. With 400 babies to deliver, giving birth can take hours. Offspring take shelter in seagrass beds, yet fewer than 1% will survive. The rest fall prey to crabs and fish, and some are so small they're even accidentally ingested by stingrays. This banded stingray moves more like a magic carpet than a critter. The stingray is one of the most ornate members of the ray family. Its stout tail has a serrated spine that delivers a painful wound. Tasmania's kelp hides even bigger predators, like the draftboard shark. It's small for a shark, only 5 feet long, but when threatened, it gulps water and balloons in size. The draftboard shark dwells deep below the surface, as far as 2,000 feet, but occasionally visits the shallows. As the kelp thins out in deeper water, a spectacle looms from the darkness. Fluorescent flower beds. The waters of Tasmania contain some of the world's richest sponge gardens, a tangle of soft corals and sea whips. They look like plants, but they're animals that ingest drifting plankton. One of the brightest in the garden is this yellow zoanthid coral. Like other coral, it taps sunlight for energy. It also draws energy from tiny algae and zooplankton. Zoanthids can contain some of the most toxic substances found in nature. Why? No one knows. Living among the sponges are some of Tasmania's most bizarre species, like the Shaw's cowfish. Its unique body is formed from fused plate-like scales, not an actual skeleton. The spineless creature comes from a family aptly known as boxfishes. Males flaunt yellow and blue markings. For females, shades of brown. If agitated, cowfish will spew toxic chemicals from their pores to deter attackers. Drifting with the tide is this rarely seen nocturnal red velvetfish. It's related to one of the world's most venomous creatures, the scorpionfish. But its toxins are much less potent. Sharp spines on its dorsal fin are fatal to other fish. The bright red skin signals danger, keeping predators at bay. The velvetfish has no defense against pollution. As runoff from mining destroys its home, the fish has become endangered. But man can also intervene to help. Less than 400 miles northeast of Tasmania, and just five miles from the Australian mainland, is the Montague Island Nature Reserve. The island is tiny, just under a mile in length. It's a popular playground for juvenile Australian fur seals. Youngsters will test their water skills and form vital bonds. In the 19th century, the fur seal was hunted for its hide and oil, to the brink of extinction. Today, they're fully protected throughout their range, but the population remains small, under 12,000. Fur seals are superb swimmers. They use their front flippers for locomotion, and their heads and necks to steer. As they dart and dive, air bubbles escaping their waterproof pelts seem to make the seas boil. Super flexible backbones let them change direction in an instant. After 40 minutes of fun, they have to surface for air. All fur seals have excellent vision, and stay alert for sharks, especially the great white. Sharks rarely catch fur seals alive. They're too fast and flexible. Hitting speeds up to 25 miles an hour, they leave most sharks behind. This Port Jackson shark captures their attention. It's combing the seafloor for sea urchins and mollusks. After investigating, the fur seals decide the shark poses no threat. On Montague, fur seals flourish, but who knows if they'll recover throughout their range. So far, conservation seems to be helping them rebound, and they're not alone. 600 miles north of Montague Island, and just 2 miles from the mainland, at the very limits of this southern water zone, lies another marine reserve known as Julian Rocks. Since 1982, this small, rocky outcrop has sheltered hundreds of tropical and temperate species. Strong currents rip around Julian Rocks, delivering schools of fish to the island. By day, black-tipped bullseye hide in one of the island's small caves. They form layers of gold, a living treasure chest. At night, they'll venture out to sea, where fewer predators lurk. One of the reserve's success stories, the wabagong shark. After decades of overfishing, it's making a comeback. Wabagongs, in the throes of mating. Males seize the opportunity, clamping onto females. With all adults roughly the same size, females aren't easily overpowered. The trick is to wrestle a female into position. The male's persistence will pay off. A female can birth up to 37 sharks. While the wabagong is one of the reserve's top predators, the grey nurse shark sits even higher up the food chain. Up to 11 feet in length and living to 35 years, the grey nurse is an icon of the southern seas. Only 500 of these magnificent creatures remain on Australia's eastern coast, and their future is shaky. But evolution has given them unique tools for survival. Green nurses have the same five senses we do, and a sixth, electro-reception. Pores under their snout let them sense electrical currents, so they can navigate the earth's magnetic field and find food. True to their nature, the sharks are top predators even before they're born. Inside their mother's womb, embryonic sharks are fighting. The strongest pups eat their siblings in a phenomenon called inter-uterine cannibalism. Out of 15 babies, only one or two will likely survive. Perhaps it is the most extreme example of survival of the fittest. But evolution may not throw them a lifeline. Wrongly accused as a man-eater, the grey nurse has been savagely hunted and decimated by fishing. Today, in the great southern seas, even the fittest struggle to survive. For millions of years, these cold waters have sheltered and nourished life. In less than a century, most of that has changed. It's hard to imagine a world void of these colorful spirits. Whether or not their ancient legacies will survive in the land down under is yet to be revealed.