The Bizarre Sea Creatures of The Great Barrier Reef

Heron Island, Australia. A surface speck overlooking an underwater empire 6,000 years old. The Great Barrier Reef. Here life ebbs and flows with the pull of the moon. By day, barracuda, sea snakes, and shovel-nosed sharks prowl the shallows. At night, an alien world comes to life. And at the reef's heart, a creation not of this world. Heron Island belongs to the Earth's largest marine sanctuary. Visible from space, Australia's Great Barrier Reef stretches over 1,250 miles, the distance from Boston to Miami. Anchoring the southern end is Heron Island. Centuries of disaster to emerge. After cyclones and quakes, broken corals and animal bones piled up. Their remains formed the beach. Over time, a rich soil developed, the seeds rooted, and a home grew for the turns. Today, more than 20 other species of bird call this sanctuary home. Green sea, loggerhead, and hawksbill turtles also come ashore to nest. It's late October, and these female green sea turtles struggle up the beach. It can take hours to find a spot to nest. They're not alone. 1,500 will come for the same reason. Some have traveled over 700 miles. Most females will lay from 30 to 100 eggs. This loggerhead weighs over 300 pounds. It takes all her strength to reach the surf. Over the next three months, she will return up to five more times to lay eggs. Once in her element, she transforms into a streamlined and weightless creature. Heron Island is ringed by a seascape built entirely from coral. 400 species of coral form the backbone of life on the Great Barrier Reef. All reefs need sun to survive. Like plants in a rainforest, corals rely on photosynthesis to turn sunlight into energy. Different shapes allow them to compete for space and light. Table corals spread out like giant solar panels. Staghorn coral grows tall rather than wide to get its share of sun. Brain corals' sheer size and weight give it access to the sun while keeping it anchored during storms. Thousands of coral colonies sprawl around Heron Island, acting as homes, nests, and feeding grounds. For small fish with no means of defense, the reef offers their only protection. Damselfish won't venture more than a few feet from home. When danger approaches, they slip between the branches. Today, the danger is yellowtail barracuda. At 20 inches, they're the smallest barracudas, but giants to smaller fish. Danger lurks around every corner of the reef, but corals aren't the only protection. Clownfish take cover in a venomous anemone. Other fish can die just by grazing the anemone's tentacles. The clownfish are protected by a mucus layer that makes them immune to the anemone's sting. The fish build up resistance over time by thickening their mucus covering. Move away and they lose immunity. If they return, it could be fatal. The anemone's first cousin is more nomadic, the jelly. Like anemones, the lion's main jelly offers safety to some creatures. With its venomous tentacles, the jelly itself seems untouchable, but not to the green sea turtle. It's immune to their toxic sting. As a juvenile, this turtle fed on jellies because they were quick and easy meals in the open ocean. Now, as an adult, it feeds strictly on vegetation. Toward sundown, schooling baitfish dance in unison like one giant organism. Their ballet signals a shift from day to night when the dynamic of the reef completely changes. On the reef, life follows the rhythm of the moon. Its magnetic pull triggers mating, breeding, and birthing for most marine life. Three months have passed since the green sea turtles laid their eggs. Tonight, hatchlings heed a summons to the sea. Pure instinct drives them toward water. Under the cloak of night, they may sneak past sharks and birds. They'll swim non-stop for at least 24 hours to put distance between themselves and shore predators. Almost a week after the turtles hatch, one of the greatest wonders of the natural world unfolds. A wave of life sweeps across Heron Island's reefs. The entire coral kingdom is reproducing. In unison, millions of corals unleash bundles of egg and sperm. This is a coral spawning. Corals reproduce in different ways, but most follow three basic steps. First, egg and sperm bundles are packaged inside the parent coral. Next, the coral releases the bundles three to eight days after the full moon. To prevent inbreeding, the bundles open and sperm leave to seek other partners. The fertilized larvae can drift hundreds of miles before finding a home. If a larvae somehow survives without being eaten, it may become the foundation of a coral colony that lives for centuries. Resembling streamers on New Year's, these party favors are actually polychaete worms. Parents reproduce by breaking off segments of their own bodies. The new strands will grow into adults up to six feet long. The streamers seem to celebrate this season of birth. The future of the reef drifts into the late night. The next morning, it's business as usual. Reef residents seek out specialists who provide premium health care. Unable to clean themselves, many rely on a tiny fish called the cleaner wrasse. Marked by distinct black and blue lateral bands, the cleaner fish never lacks for customers. Darting in and out of the gills and mouth, the cleaners remove debris, parasites, and infected tissue. Without their help, most reef fish could succumb to infection. Not all relationships are mutually beneficial. A Napoleon wrasse is shadowed by two pesky remora, and they're not here to clean him. They're here for protection, transportation, and leftovers. The Napoleon wrasse can reach over 500 pounds by gorging on sea urchins, mollusks, crabs, and shrimp. Without the reef, he won't survive. CO2 emissions worldwide are lowering the ocean's pH levels. Healthy corals like these are at risk. Seventy percent of the world's reefs are damaged or are dying. Heron Island may be suffering the worst trauma in its history. Global warming isn't the only threat. An army of invaders advances from the north. Like vampires, the crown-of-thorns sea stars are sucking the life from reefs. Once they wrap their arms around healthy coral, it's all over. Their digestive fluids dissolve the coral's tissues, leaving behind a white skeleton. It's utter devastation. Covered with venomous thorns, the sea star has few predators. It takes a special hunter to eat a crown-of-thorns, the giant triton snail. It can sniff out and chase down the sea star. The snail pins down the star with a sticky foot. It pierces the star and injects paralyzing saliva before feasting at its leisure. A triton can devour a crown-of-thorns in three hours, but can only eat one per week. Crowns reproduce faster than tritons can devour them. The crown-of-thorns has always lived off the reef. It kept fast-growing corals in check so slower ones could take root. But lately, mankind has thrown nature out of whack. Farm fertilizers running into the sea cause more algae to grow. Baby sea stars eat algae until they're two years old, then switch to live coral. With so much extra algae, the sea star population has exploded. An estimated one million crown-of-thorns are ravaging the Great Barrier Reef. It's only a matter of time before they reach Heron Island. The sea stars have already devastated huge swaths of the Great Barrier Reef. Almost 400 miles north of Heron Island, an unusual reef remains safe from the crown-of-thorns. It sits alone in the open ocean. The seabed here is smooth and sandy, but coral polyps need a hard surface to attach to. And therein lies the mystery. A reef where none should be. Man is destroying the world's reefs, but inadvertently he helped create this one. A product of human engineering and natural disaster. This reef was once a luxury liner. In 1911, 121 passengers and crew died when a cyclone sank their ship while traveling along Australia's coast. The SS Yungala lay undiscovered for 50 years. Today, only a steely skeleton remains. The ship has become a vibrant, living memorial. The wreck is more than 350 feet long, and every square inch is festooned with corals, sponges, and mollusks. This decorator crab is a master of disguise. Using sticky saliva, it glues pieces of the reef to hook-shaped hairs on its shell. If it moves into new turf, the crab will redecorate itself to blend in. Predators constantly inspect the wreck. Using its flat tail like a rudder, the olive sea snake navigates around the ship looking for prey. Crabs, fish eggs, even eels are fair game. At six feet long and highly venomous, this predator has little to fear. A resident hawksbill searches what was once the deck for dinner. She'll spend most of the evening plucking ripe sponges. By removing sponges, she frees space for new communities to settle. But the reef is still a ship. Eventually, the steel beams will crumble and the rusty shell will collapse into the sand. With nothing to hold on to, the corals cannot survive, and the reef's residents will move on. The Great Barrier Reef still reigns as one of the world's seven natural wonders. Soft corals capture the essence of the reef, both fragile and resilient. Global warming will take decades to reverse. Reefs worldwide will keep dying. But places like the Yangala offer a glimmer of hope. It's a signal of nature's ultimate adaptability and tenacity to survive.