Inside the Great Barrier Reef – Nature’s Underwater Paradise | Full Documentary

Nature is not a place to visit. It's our home. Nature is all that we see. Animals, insects, disappearing into their surroundings. Using deceptions, disguises, lures. Nature is all that we hear. The call of an eagle. The hiss of ocean spray. The rumble of thunder. The doings of a cricket. The wonderful beauty of nature. The crucial, fragile affinity between animal life and their environment. All of this is World of the Wild. The Great Barrier Reef. The largest coral reef system in the world. It stretches for over 2,300 kilometres along the east coast of Australia. Comprised of billions of tiny life forms known as coral polyps, the reef is the largest structure on Earth made from living organisms. So large that it is visible from outer space. With the continent of Australia uplifting into its solitary position tens of millions of years ago, the land mass was raised above normal sea levels, creating a base platform for the reef at the perfect depth for corals to flourish. In this episode, we delve into the waters of the coral sea to explore its colourful environment and examine the diverse animal life that it's home to. We will search for the concealed octopus, follow green sea turtles on their journeys, comb the seagrass with dugongs, learn the secrets of jellyfish, and hunt with white-tip reef sharks. Teeming with life, the Great Barrier Reef supports a densely interwoven ecosystem. Taking advantage of the coral infrastructure, octopuses are among the most intelligent and versatile of the reef's inhabitants. Perfectly adapted to life among the nooks and crannies of this maze-like construction of the reef system, octopuses lack any sort of skeleton, making them remarkable contortionists. Squeezing into the most improbable spaces, the octopus is able to both protect itself from predators and launch ambush attacks on passing prey. All octopuses are venomous, but one takes this adaptation to the extreme, the blue-ringed octopus. Despite their small stature, blue rings are one of the world's most venomous marine animals. Powerful enough to kill creatures far larger than itself, at any one time a single blue-ringed octopus carries enough venom to kill 26 humans within minutes. Navigating the reef system by expelling water in a form of jet propulsion, the blue ring spends the majority of its time hiding in the coral crevices. Masters of disguise, not only can blue rings change their colour in a split second, but they are also able to alter the texture of their skin in order to blend seamlessly with their surroundings. And the blue ring employs it to deadly effect when pursuing its preferred prey, the small crabs and shrimp. Hunting by vision, when stalking prey in the open, the blue ring blends so effectively with its environment that it can steadily approach its quarry and attack before the victim knows what hit it. Seizing prey with its tentacles, the blue-ringed octopus uses its horny beak-like mouth to puncture through the crustacean's exoskeleton and deliver a different kind of venom, Reserving their most potent venom for self-defence, blue rings administer a less potent toxin in hunting. The effect is the same, paralyzing the victim in seconds and allowing the octopus to safely consume its quarry. Facing few threats in the wild, the greatest danger to the blue-ringed octopus is the degradation of its ocean habitat. In the case of the Great Barrier Reef, the coral that underpins the entire ecosystem faces an uncertain future. With 80% of the land adjacent to the reef used for farming, the runoff from fertilizer and pesticides is a major health risk for the reef and the life it supports. As the connectivity between the environments of the land and the sea are becoming more widely understood, integrated management plans are needed to ensure the future of the blue ring, the reef and all the life it supports. Of the seven species of marine turtle, six can be found in the Great Barrier Reef. The most abundant of these is the green sea turtle, which has its nesting grounds on the islands of the reef system. Feeding on the abundant sea grasses and algae of the warm waters of the coral sea, adult turtles are exclusively herbivores. Juveniles, however, have a broader, more carnivorous diet, targeting animal life including crustaceans and jellyfish. Whether in the open water or tucked into the crevices of the reef system, green sea turtles know few natural predators, thanks to the evolution of their shell. Streamlined for effective swimming, this armoured carapace encloses the vital organs and is all but impenetrable to attack. Only large sharks stand a chance against the robust shield, and even then, green sea turtles can be surprisingly difficult to catch. Despite their slow-moving reputation, turtles are powerful swimmers, and when threatened, employ their paddle-like flippers to reach underwater speeds of over 55 kilometres an hour. For these migrating turtles, the Great Barrier Reef is not just a breeding ground, but a cleaning station. Throughout the reef system, turtles have developed a symbiotic relationship with various species of cleaning fish. This mutually beneficial arrangement sees the fish given an easy feast, and the turtles relieved of the tiny parasites that come to congregate on their shells. Taking decades to reach sexual maturity, females do not breed until they are around 45 years old. And while males annually visit the sheltered breeding sites of the Great Barrier Reef, females only breed every two to four years. When she is in a breeding year, the female controls the process, mating with multiple males to fertilise her clutch of over 100 eggs. Then, along with her fellow gestating females, she makes the arduous journey to the surface. With almost a thousand islands dotted throughout the Great Barrier Reef, green sea turtles have a range of nesting areas. Graceful creatures in the sea, the laying females face an exhausting journey on land as they drag their near 200 kilogram bulks up the beaches in order to bury their nests beneath the sand. This is goodbye for the mother and her young. She will not stay with her children. Instead, she is heading back to the waters of the Coral Sea. Around ten weeks later, the eggs hatch. Surfacing en masse, they make their perilous journey back to the sea. This process of crossing the beach is thought to imprint the hatchlings with the cues they need to find their way back when it is their time to breed. But many will not make it. With their mothers long gone, the hatchlings must fend for themselves against predators such as crabs that pick the vulnerable turtles off as easy meals. For the green sea turtle this, their first journey from nest to sea, is the most dangerous of their lives. And even for those that manage to swim away, the future is far from certain for this endangered species. The Great Barrier Reef ecosystem is not all about coral, with shallower sections of this marine environment encompassing large sandy tracts dominated by seagrasses and other plant species. Specialized for life in this niche environment of underwater meadows is the sea cow, otherwise known as the dugong. Capable of diving to almost 40 meters, these oxygen-breathing mammals prefer the shallower waters between the reef and coastline. Here, in depths averaging 10 meters, the seagrass beds they depend on are most abundant. Highly specialized marine herbivores, dugongs have adapted perfectly to their grazing lifestyle. Their elongated snouts face downwards, ending in enlarged, muscular upper lips. Pressing these lips to the seafloor, they sift through and pull out entire plants, including the roots, shaking them free of sand before ingesting large mouthfuls. While they may look like giant vacuum cleaners running indiscriminately along the seafloor, in the Great Barrier Reef, the dugongs avoid bulk eating by targeting high-nitrogen, low-fiber varieties of seagrass. Coastal development, boat traffic and pollution all degrade seagrass communities, and it is these anthropogenic factors that are endangering the future of the dugong. Because they are evolved for such a specific marine environment, to protect the seagrass habitat is to protect the dugong. Social animals, dugongs are rarely seen in large numbers because of the lack of seagrass beds to support them. However, in times of plenty, herds in their hundreds have been witnessed coming together. While numbers of this shy and elusive creature are difficult to gauge, the Great Barrier Reef is considered to support a stable and healthy dugong population. Although fishing-related fatalities continue to occur, dugongs are protected in many countries by strict anti-hunting laws. Slow-moving creatures, the average speed of a dugong is just 10 km per hour, even less when feeding. This gentle pace allows for fish such as remoras to travel with the dugongs, cleaning them of the parasites that settle on their skin. Long-lived mammals with a lifespan of around 70 years and a slow reproduction rate, preserving this endangered species will require a sustained commitment for many years to come. The corals of the Great Barrier Reef are living things, made up of colonies of thousands of organisms growing over the calcified remains of their ancestors. Linked by their simple anatomical design and carnivorous feeding habits, corals are part of a group of animals called cnidarians. The basis of the Great Barrier Reef are tiny, stony coral organisms called polyps. Members of the cnidarian family, when these polyps attached to the continental shelf around Australia's northeast coast, they divided into thousands of clones to form colonies. As polyps are soft-bodied, they secrete a protective limestone skeleton around themselves, and in this way, the reef was formed over millions of years by billions of polyps. Gradually growing by around a centimetre each year, the coral reached up toward the light like trees in a rainforest, and once at the surface, spread outward to create the stunning formations we know today. Vastly different in appearance, the free-floating cnidarian cousin of the coral is the jellyfish. While the sedentary corals of the Great Barrier Reef required clear, sunlit waters at a very particular depth range, the mobile jellyfish is far less fussy, and can be found in almost every ocean on the planet. A non-polyp form of cnidaria, the name jellyfish is somewhat of a misnomer, as invertebrates, they lack a spine, and therefore are not true fish. Fish they may not be, but jellies are actually the most energy-efficient swimmers in the ocean. While they lack speed, and have only limited control over their movement, the jellyfish's pulsating motion creates a tiny vortex effect in the water, demonstrated to provide effective transport with a minimum energy output. As carnivores, jellies feed on the plankton, crustaceans, even other jellies that are abundant throughout the reef. Each tentacle houses thousands of tiny cells containing stinging, thread-like harpoons, called nematocysts. When a tentacle happens to brush against prey, the nematocysts uncoil, piercing the victim's flesh, and injecting their paralyzing venom. Found in the offshore waters of the reef during the tropical wet season, box jellyfish are considered among the most venomous animals in the world. While jellies feed on small fish, certain fish species of the reef have evolved a symbiotic relationship with their would-be predator. With an immunity to the stinging nematocysts, these fishes shelter among the otherwise deadly tentacles, gaining protection from other ocean predators. Having wandered the seas for over 500 million years, jellyfish are considered the oldest multi-organ animal on the planet. In evolutionary terms, simplicity is often the best, and there is evidence that jellyfish numbers are increasing globally despite changes in the oceans that are unfavorable for other species. Recent research is suggesting that jellyfish are resistant to ocean acidification caused by global warming, and while creatures such as sharks, tuna, and sea turtles may prey on jellyfish, overfishing is reducing many of their predators. So, while greenhouse gases and intensive fishing are having a harmful effect on the reef and most of the life it harbors, it seems that the humble and ancient jellyfish is able to float on as it has for millennia. With an abundance of life comes an abundance of predators, and the Great Barrier Reef is no different. Of the variety of sharks that inhabit the teeming waters of the reef's rich ecosystem, the white-tip reef shark is the true specialist of this coral environment. One of the most common sharks found on the reef, the white-tip is relatively small, around 1.5 meters in length, and has a slender build which allows it to pursue prey through the cracks and crevices of the coral. In fact, the white-tip's lithe, elongated body is so specifically designed for hunting in tight spaces that it must swim with a strong, undulating motion, making it quite clumsy in open-water hunting. Although vulnerable to predation from other, larger shark species, white-tip reef sharks remain an apex predator on the Great Barrier Reef, controlling populations of fish, crustaceans and octopuses. While they may hunt opportunistically during the day, white-tips are nocturnal creatures, and with the onset of dusk, the true nature of the white-tip is revealed. Methodically patrolling the coral reef in loosely organized groups, white-tip reef sharks hunt by smell and by employing their sixth sense, detecting the faint electrical fields generated by their prey. The white-tip's remarkable sense of electro-reception allows them to locate creatures hiding or sleeping within the coral, forcing their way into the holes of the reef face, often with enough vigor to break the coral and damage their own skin. White-tips feed on the plentiful aquatic life sheltering within the reef, like goatfish and parrotfish. Hunting in packs, the relentless white-tips work together to drive out prey, but do not share the spoils. Unlike grey reef sharks or their black-tip counterparts, the competitive feeding of white-tips is more well-mannered and does not stir them into feeding frenzies. After dawn, the new day will find the sociable white-tips recovering from their busy nights. Resting in groups, they have the rare ability among sharks to remain motionless, pumping water over their gills to allow respiration. So well-adapted to their reef-hunting lifestyle, white-tips do not require an extensive reign. Tending to occupy small patches of reef, around a square kilometre in size, they rarely venture far from their modest home range. With diminishing numbers, the white-tip reef shark's limited range and slow reproduction rate has seen them classified as a near-threatened species. Fortunately, in the Great Barrier Reef, the no-entry zones boast populations 80% higher than in fishing zones, and this method of conservation has demonstrated a solution for preserving the species of expert coral hunters. Recognised as one of the seven wonders of the natural world, the Great Barrier Reef is a beautiful marine environment brimming with life. In this episode, we have seen octopuses, green sea turtles, dugongs, jellyfish and white-tip reef shark. Such an extensive reef system is subject to a range of challenges. Increasing water temperatures are already taking their toll on the fragile corals, and these changing conditions have allowed the coral-eating crown of thorn starfish to flourish. Considered rainforests of the sea, the shallow coral reef system is one of the most diverse ecosystems on the planet, and with dedicated management, the hope is that it can remain so for generations to come.