Palau Underwater: Manta Rays, Ancient Reefs, and Jellyfish Lake

Palau, a remote and tiny island chain near the equator, is home to one of the world's richest reef ecosystems. It is also home to giants. Massive Second World War wrecks harbor dark secrets on the ocean floor. I turn around, there's a huge monster wreck behind me. My heart went whoop! Undersea trenches, deep enough to swallow mountains, offer a glimpse into the abyss. The old phrase that we know more about the surface of the moon and Mars than we know about the bottom of the ocean holds true. And large and mysterious creatures soar through its azure waters. You turn around and all you see is these big gaping mouths coming out of the blue. It's basically like a mouth with wings on it coming at you. Here, in this land of the giants, at the southern end of the Palau Islands, near a dive site called German Channel, manta researcher Mandy Eptuson prepares to descend into the blue. During the German occupation of Palau, prior to the First World War, miners blasted and dredged a channel here to create a shipping route between the islands. Today, strong currents carry plankton to the mouth of the channel, making it an ideal feeding site for one of the ocean's most graceful and gentle giants, the manta ray. One of the largest creatures in the sea survives by feeding almost entirely on one of the smallest. It's sort of like a bottleneck, so the plankton gets concentrated here, and that's why it's famous for mantas. So we're hoping to see mantas, obviously, and if we're lucky, maybe a new individual that hasn't been recorded yet, so we can add it to our database. Mandy began the Palau Manta ID project in 2009, identifying each animal by the spots on its belly. The spot formation on a manta is as unique as a fingerprint. We started taking pictures of the bellies to identify the mantas, and trying to show, especially Palau government, that we don't need to hurt the animals or attack them to be able to find out more about them. We've identified over 280 right now. Five years ago, nobody would have believed we have that many mantas in Palau. A simple ID project can do a lot. By tracking the numbers and movements of mantas, Mandy and the UK-based Manta Trust can identify any population decline caused by illegal fishing, and whether or not tourism may be driving mantas away from German Channel. Tourism is on the rise in Palau, a collection of more than 200 islands nearly 1,000 miles east of the Philippines, in the western Pacific Ocean. The tourists that flock here to explore its natural wonders contribute about $125 million to the economy, more than half of Palau's gross domestic product. Hundreds of miles of sky-blue oceans surround the archipelago. Limestone islands, blanketed in thick and pristine jungle, rise like mushrooms from the sea. They appear to be floating gardens. Scuba divers from across the globe are drawn to Palau for what lies beneath the emerald lagoons, one of the world's richest reef ecosystems. These coral gardens overflow with 1,500 species of fish, 500 species of coral, and more than 100 species of sharks and rays. Palau's seas may contain more species of marine life than anywhere else on Earth, and provide researchers an exceptional window into a vanishing underwater world. The explosion of marine life here is due to marine geology. Palau sits on the tip of an underwater mountain that formed 70 million years ago. Far below the island peaks, currents crash against the drowned mountain, then surge upward, carrying the nutrients that underpin the oceanic food chain. There is another reason for the sheer numbers of fish that throng these waters. Palau has a long history of conservation. For centuries, Palauans have lived in harmony with the sea, never taking more than they needed. In 2009, Palau created the world's first shark sanctuary, making it illegal to catch sharks in its seas. Then in 2014, it expanded its conservation efforts and banned all foreign fishing within its waters. Palau is now home to the world's largest marine sanctuary, a swath of protected ocean nearly the size of California. Marine law officers patrol the Palauan seas, on the lookout for illegal fishing vessels. As a result, the big fish that have been all but wiped out in some areas of the Pacific are still very much alive in Palau. Hefty gray reef sharks, five-foot-long Napoleon wrasses, and of course, manta rays, the marine giants that patrol these seas. Though smaller than their oceanic cousins, reef mantas are still among the largest fish in the sea. They have an average wingspan of 11 feet and reach weights of more than 3,000 pounds. Mantas have exceptionally large brains, specifically the region responsible for hearing, touch, and vision. They are highly social and curious about humans. If you've been diving a long time, you interact with different animals. You can see the difference, for instance, between a guppy or a Napoleon wrasse. A Napoleon wrasse, you can tell there's somebody home, there's an intelligent being in there. And it's the same with mantas. When you look at them and you start realizing they're actually, in my opinion, they can recognize certain dive guides. They will go over a dive group and go straight for the dive guide. And especially the newborn mantas, they will play with divers when it's not too crowded. You can see it's an intelligent animal, like a dog or a cat, and they can learn. At German Channel, mantas swim against the current to feed on large concentrations of plankton swept into the channel entrance. Fins curving around its face direct water into the manta's large open mouth. You turn around and all you see is these big gaping mouths coming out of the blue. It's basically like a mouth with wings on it coming at you. It's an amazing sight. Tissue between the manta's gills sift tiny crustaceans and plankton from the water. A manta is like a giant filtering machine capable of vacuuming up more than 400 pounds of plankton in a single week. At times, manta feeding can be a dizzying display. Depending on the current and the wind direction, sometimes they'll feed by themselves and roll. They call it barrel rolling. It's like an underwater ballet. Really nice to watch. The manta may look like it's chasing its tail, but by rolling, it pushes more plankton into its waiting mouth. When the current is strong, usually right before a full moon, mantas adopt an entirely different but equally captivating feeding strategy known as train feeding. So you can get anywhere from 2 to 20 or 200, if there are that many, feeding together in a train, which is an amazing sight. And they'll just keep going back and forth across the line where the plankton gets trapped. One of the largest creatures in the sea, mantas are also one of the most mysterious. Research into their mating and birthing behavior has barely begun. For hundreds of years, mantas were simply known as devil fish due to their imposing size and bat-like appearance. But they're very, very gentle. When the current's strong, sometimes when you're taking photos or video, it's very hard to stay out of their way, especially when there's that many of them. So when you're freediving and you dive down to take a picture, they'll come straight at you, and sometimes you get thrown in their path, basically. And they'll just very gently lift their wing and try not to touch you. They're very careful with people, which is amazing. They could just slap you, you know, if they wanted to. Mandy believes that physically tagging mantas can cause harm to these gentle giants. A manta's skin is like rubber, and wounds can take years to heal. Even though they might be able to recover from it, it leaves scars, and by photographing the mantas at German Channel, we've seen how long it can take for those scars to heal. By photographing them every season, you can start seeing those results. So we prefer to not do actual tagging. Previous tagging studies enabled scientists to track the movement of mantas. Photo IDs can't do that, but Mandy has developed an alternative that is unveiling more secrets of their behavior. She places time-lapse cameras at the cleaning stations, spots on the reef where small fish rid the mantas of dead skin and parasites. It takes pictures every 10 seconds or 30 seconds, and normally we put four or five around the cleaning station, and then when you pick it up, you've got thousands of pictures to go through. In the previous year, Mandy was able to identify 44 new mantas from thousands of time-lapse photos. It's a lot of effort, but worth it in the end. Because instead of acoustic tagging where you can just see a beep how many times a manta passed by, you can actually see the manta and what they're doing and learn about their behavior at the same time without hurting them. Mantas are curious creatures and will closely inspect the cameras left behind on the reef. When we put the time-lapse cameras, we start realizing that they're immediately aware of something changing in their cleaning station. So they come up to the cameras and they unfold their cephalic flaps, which are sort of like feelers for them also. So they're doing like this to the camera to see like what is this thing that's sitting on my cleaning station. So those are the kind of things you would never find out any other way. Today at German Channel, one of the busiest manta sites in Palau, there are no mantas to be seen. Currents, which should be incoming based on the moon cycle, have switched to outgoing, which means no plankton is flowing into the channel, and that means fewer mantas. Mandy spots something on the bottom, a feather-tailed stingray, buried up to its eyes in the sand. Finally, she sights a large male manta. It's one called Uncle Fester, a regular at German Channel that has fed here for at least ten years. On this day, Mandy sights just three other mantas, one pregnant female, already logged in the database, and two others that passed by without stopping at the cleaning station. Mantas may be large, but they are dwarfed by another giant living in the waters of Palau. Its barrier reef. Coral reefs are the world's largest living structures, made up of millions of tiny plant-like animals known as coral polyps. Reefs begin when a polyp attaches itself to a surface on the ocean floor, then divides into thousands of clones, which secrete a calcium carbonate skeleton. Together, the polyps act as a single, immense organism. Coral reefs are always growing. When coral dies, it leaves behind the rock-like skeleton. The next generation of coral grows on the old skeleton. Coral reefs are the rainforests of the sea. They cover fewer than 2% of the ocean floor, and yet they provide food and shelter for about one quarter of all ocean species. One billion people depend on coral reefs for food and income from fishing and tourism. Reefs also provide protection from hurricanes and typhoons. The Palau Reef, believed to have formed about 2 million years ago, may be the most essential giant in these waters. The bone-white beaches of the low-lying rock islands are built from sand that originated as coral. Reef animals like this parrotfish feed on coral and algae that grows on the surface of the reef. The parrotfish's hard, beak-like teeth bite off not just the coral, but its hard skeleton as well. The pulverized hard coral material ingested by the fish passes through its digestive system and is deposited back into the ocean in clouds of fine white coral sand. One parrotfish can produce 200 pounds of sand in a single year. These rock islands, built by coral sand and topped by lush and untouched Pacific jungle, are a major tourist draw. Palau is a country of just 20,000 people. In 2015, it received more than 150,000 visitors. This tiny island nation is struggling to find a balance between the profit tourism generates and its impact on the reef. You know, if you have one or two people, you know, and they go there and they do a little bit damage, it's not a big deal. But if you have thousands and thousands of people doing that every day, then, you know, eventually we would destroy the corals and destroy the structure. The research that we're doing is to look at the sites that are visited by tourists and to try to look at their impact on the reef communities, including the corals and the fish and the animals that live around the reef. Today we're trying to look to see the impacts of snorkelers on shallow coral reefs. So with Palau's tourism boom, we've seen an increase of tourists on our snorkeling reefs. And a lot of them, as we've noticed, have very little or little confident swimming skills. So we want to see if that has any impact on the corals and if they're breaking corals or standing on them and the effects of that. To determine the health of the coral at this site, Evelyn uses a sampling square called a quadrat. She throws it randomly 50 to 60 times at a given site. When the quadrat lands on the lagoon floor, she photographs the area within the frame. Researchers study the photos for evidence of coral damage and compare the sample photos taken at busy snorkeling sites with those taken at sites untouched by tourists. Initial research by Dr. Gobu's team reveals that the reefs at crowded snorkeling sites are dominated by broken coral, which seriously threatens the health of the reef. But the team is studying more than just corals today. Gary is going to be counting fish today. He's one of our experts at the Coral Reef Centre. He knows a lot of our fish species, their common names, their Palauan names, as well as their Latin names. So what he will do is he will go and measure any fish that comes within a five metre radius of him. It's what we call a stationary fish count. So he'll stay in one spot for three minutes and he'll count any commercially important fish that comes in that five metre radius and then write down their sizes in centimetres. The fish count, like the reef survey, is designed to assess the impact of tourism on the lagoon. Although it's prohibited, tour operators have been known to feed fish to attract them to tourist snorkeling sites. Hand-feeding fish makes them associate humans with food and can interfere with their natural feeding cycles. This study will help determine the effect fish feeding has had on both the size and numbers of fish in the lagoon. On a global level, coral reefs face a threat far greater than tourism. Ocean acidification. Humans have produced more and more carbon dioxide emissions through the burning of fossil fuels. More than one quarter of carbon dioxide pumped into the atmosphere is dissolved into the oceans, where it upsets the chemical balance, making water more acidic. The acidification threatens the survival of the animals on the reef. The skeletons of most marine organisms, including crustaceans and fish, are made from calcium carbonate. If the acidity of the water increases, there are fewer carbonate ions in the water, and it becomes harder for these animals to form a skeleton. Acidity can be increased to the point where even coral can no longer make a skeleton. Even before that stage, the struggle to make a skeleton can leave coral weak and vulnerable. You might have a coral, but it's not strong. And it's able, like a little storm, and it would break. Or you would have very high bio-erosion. A lot of other organisms would be able to live inside and break a skeleton of a coral. It's yet another threat on the Palau Barrier Reef that was already stressed by reckless overfishing. For decades, foreign fishing vessels plundered these seas, brutally raking fish from the reef. The reef is an ecosystem, and you need corals and you need fish. And if you take all the fish from the system, then it will affect the reefs. It will affect its health and its recovery from disturbance. And so that is one of the main issues that we need to ensure, that we still have enough fish in the reef to allow the reef function to continue. Not all of Palau's reefs are 2 million years old. Some are relative youngsters that can be traced back just 70 years, to a time when battles raged over Palau's tropical skies. At the bottom of Malakau Harbor, a massive broken skeleton appears slowly from the blue. It is the Iro, a Japanese Navy tanker that met its doom during the Second World War, when U.S. airplanes rained explosives on the Japanese fleet. Over the decades, the Iro has transformed into an artificial reef, providing shelter for prey, food for predators, and a breeding ground for the hard and soft corals that have taken hold of the ship. She's a spectacular wreck to dive now. She is teeming with life, and it's just an amazing wreck dive, because you have all that history, you have all that drama of the sinking of the vessel, and now, 70 years plus later, you look at it, and it's just the most beautiful, spectacular reef there is around there. The Iro sits upright in its watery grave, 130 feet below the surface. It's a colossal wreck, nearly 500 feet long, weighing upwards of 14,000 tons, and remains largely intact, except for the damage caused when a massive explosion in the engine room sent the ship to the bottom. On the bow sits a turret gun, its barrel an armored shield draped in soft coral. Wrecks like the Iro provide a stable setting for coral. Corals spawn in the water column. Eggs are carried by the current and can land anywhere. The shallow depth, warm water, and relative stillness of this lagoon make an ideal breeding ground for the algae that cements coral reefs together. The Iro is alive with stony staghorn coral. Ivory tube sponges and black coral trees. Fish make their home on or near the wreck as well. Clouds of fry, lionfish, and Pacific spadefish. Three masts reach toward a distant sky and provide an ideal surface for sun-seeking organisms, including huge colonies of bubble-tip anemones. A close relative of both jellyfish and coral, the bubble-tip anemone is equipped with sweeping venom-filled tentacles that ensnare passing prey. The slightest touch triggers the tentacles, which inject a paralyzing neurotoxin into its victim, but not to the tomato clownfish nestled inside its tentacles. To defend itself and ensure it has enough to eat, the bubble-tip anemone forms an unlikely alliance. A layer of mucus on the clownfish's skin makes it immune to the anemone's lethal sting. It's a symbiotic relationship. The anemone protects the clownfish from predators and snacks on its leftover meals. In return, the clownfish drives off intruders and cleans the anemone of parasites. The coral-encrusted Iroh is just one of more than 60 Second World War wrecks in Palau. In March 1944, U.S. Navy planes appeared high above the islands, bombarding the Japanese fleet with rockets and torpedoes and sending most of its vessels to the bottom. The coordinated attack was codenamed Operation Desecrate I. In September 1944, the island of Peleliu was the scene of one of the bloodiest battles of the Second World War. U.S. Marines made an amphibious assault on these beaches to liberate the island from Japanese forces. Fighting lasted for months and took the lives of 10,000 Japanese and 1,800 American soldiers. Today, the island is surreally peaceful. Although scattered amid the lush vegetation are the reminders of past horrors. A crippled Japanese fighter plane reclaimed by the jungle. A gutted U.S. Marine landing craft corroded by the elements. And sobering memorials to the thousands, Japanese and American, that spent their final moments on what was once an island paradise. Francis Torabeyong is a native Palauan who grew up on the islands in the years following the war. He founded Palau's first dive operation and, in the 1980s, helped discover more than 30 Japanese wrecks, including the 285-foot-long Chuyomaru. Like the Iro, it sits upright and is overgrown with corals, sponges, and oysters. The Chuyomaru was a coastal freighter sent to the bottom during Operation Desecrate I and discovered by Torabeyong in 1989. Because it's a huge thing, right behind me. I did not see it because I was going down this way. That was exciting. I mean, that completely changed my way of diving. Today, when I take people diving, I don't try to explain everything. I talk about safety, the depth, time, and how we go around this wreck. And I tell them, that's good enough. I don't want to go beyond that. Why? I say, I want you to have that excitement like I do. I want you to have that feeling. It's hard to explain, but when things are in the water for the last 50-some years, 70 years, and then the first time you go, it's a really exciting dive. The Chuyomaru shares its watery grave with a mystery ship. Its true name remains unknown. No records of the ship can be found in Japanese Navy archives. Though like most wrecks in Palau, it was sunk along with most of the Japanese fleet during Operation Desecrate I. Today, it's known simply as the Helmet Wreck or Depth Charge Wreck for the dozens of bombs found in its hold. Divers are warned not to touch any of the charges. Many of Palau's wrecks are laden with live ammunition that can explode if disturbed. In fact, it's illegal for divers to take anything from Palau's sunken historical treasures. The Depth Charge Wreck is a trove of Second World War artifacts. The cylinder poking out of the wreck is a clinometer used to measure the height of clouds to predict incoming storms. These sake bottles and a corroded Japanese gas mask are grim reminders that men died here in what is now a living museum of the sea. When I took the Japanese diving there, I can see they have a good pump. They tell me a little bit eerie. That's the way they do. I respect that. So it's part of history and part of our relationship with Japan and something that people need to understand that we need to respect other people. These once mighty wrecks won't last forever. Saltwater corrodes and eats away at the steel skeletons. Eventually, the lagoon will swallow these remains. Over the eons, saltwater erosion has also carved stunning caverns and tunnels into Palau's limestone geography. Hidden 12 feet below the surface, Chandelier Cave is one of the largest cave systems in Palau. At one time, it was an open-air cave on the surface of the Rock Islands. After the last ice age, oceans rose, filling the cave with seawater and concealing the entrance. Stalactites, formed from calcite deposited by water dripping from the cave ceiling, hang like glittering light fixtures, giving Chandelier Cave its name. Inside the cave, there is no sunlight to nourish plankton. Free from these microscopic organisms, the water is crystal clear. At Ceaus Tunnel, divers drop down to enter a chamber that reaches depths of more than 140 feet. Even this far below the surface, sunlight penetrates the tunnel to illuminate gorgeous orange sea fans and lionfish nibbling on soft corals. Palau is a jumping-off point for some of the deepest diving in the Pacific. It sits atop what is essentially a sunken mountain range. A steep drop-off, more than 30,000 feet deep, fringes the islands. This is the Palau Trench. It just drops off, and it plummets into the abyss, and very, very close to shore as well. So people always talk about the Marianas Trench, the deepest part of the planet, Challenger Deep. That's nearly 300 kilometers offshore. We've got massively deep water within 15 or 20 kilometers of our shoreline, so it's very, very unique. The Palau Trench is deep enough to completely submerge Mount Everest. Scuba divers typically descend about 130 feet, less than half of 1% of the depth of the trench. Divers have only just scratched its surface. What is known about what's down the Palau Trench, honestly, very, very little. The old phrase that we've all heard, that we know more about the surface of the moon and Mars than we know about the bottom of the ocean, holds true. Collins has compiled a 3D map of the trench from satellite-derived gravity data and sonar measurements collected on dives. The green shows the Palau Islands, just the tip of a massive underwater mountain. You can see that some of these sheer walls, they plummet miles, literally miles, two or three miles, before they might have a slight shelf, another feature, and again before they just plummet into the abyssal plain at over 9,000 meters deep. Once we look over the edge of that reef, sometimes it's a little daunting, because you have the beautiful colors, the shallow waters, and you just look over and it's literally looking down a cliff, and especially knowing how deep that is. So sometimes it can be a little bit daunting and a little bit disorientating, but it's also a bit thrilling. A short boat ride from Siez Tunnel lies a marine environment so spectacular it's considered one of the seven underwater wonders of the world. Palau is home to more than 50 marine lakes. When glaciers melted at the end of the last ice age 10,000 years ago, ocean levels rose, filling low-lying areas with seawater. Fissures and tunnels in the limestone connect these saltwater lakes to the ocean. Beneath the surface of a 100-foot deep marine lake, on the uninhabited coral island of El Malik, is an astonishing sight. Millions of rippling jellyfish pack the fluorescent green water, their shimmering bodies casting a luminescent glow. This is Jellyfish Lake. These golden jellyfish have thrived in the lake for more than 10,000 years. In this closed system, there are few predators, so the jellyfish have lost their need to sting. They possess stinging cells, just not ones powerful enough to cause serious harm to humans. Getting to swim through that many jellyfish is a pretty weird but wonderful experience. When you find a very dense patch of them, the whole lake is essentially pulsating these jellyfish, so it's very cool to see. They're not harmful unless you have very sensitive skin. They're very soft. They're just doing their own thing, cruising along. There's another, even more remarkable way in which these jellyfish differ from their cousins in Palau's nearby ocean lagoons. Most species of jellyfish, like this moon jelly, drift serenely on ocean currents, just as their ancestors have since before the age of the dinosaurs. The 5 million specimens at Jellyfish Lake are far from passive. They may look like they're drifting aimlessly, but in fact, they're on a journey. Migrating almost a mile, they follow the same path and same schedule every day. As the sun rises in the east, the jellyfish swim toward its life-giving rays. They have to make the trek to survive. The body of each jellyfish contains a crop of algae, its main source of food. The algae processes sunlight to produce sugar that feeds the jellyfish. For hours, they swim east toward the sun, pumping water through their bells and rotating counterclockwise to provide even exposure to the sun for the algae in their bodies. Trees that surround and shelter the lake also cast shadows on the surface. The jellyfish must avoid the shade. They need to absorb as much sunlight as possible to maximize the energy created by the algae within their bells. So what they do is they follow the sun around the lake. So at a given time during the day, they'll be in the brightest spot of the lake finding the most food. As the sun begins to set in the west, the dense bloom of jellyfish reverses course and heads back to the western shore. All this swimming churns up nutrients in the water that form the base of the lake's food chain. When the sun disappears into the horizon, the jellyfish sink 50 feet down, where nitrogen-rich waters help sustain the algae in their bodies, before ascending to the surface before dawn to start their complex migration once more. Of Palau's 52 marine lakes, five are home to persistent populations of golden jellyfish. Fragile creatures, they have shown an outstanding ability to adapt in these landlocked lakes, lakes that were once connected to the ocean that defines and sustains this tiny island nation. For thousands of years, Palauans have depended on their coral reef for survival. It's such a diverse habitat. So if we lose that, we really lost a lot of our ocean, a lot of the biodiversity in our ocean. Billions of people live near the coast and they depend on coral reefs. So all of those, and especially us on these small islands, you know, we would be severely affected and our way of life, you know, is totally changed. It would be a devastation to us, you know, not to have the reef. These Pacific Islanders hold two traditions of deep respect for the sea. Yesterday, one of my customers asked me, Francis, don't you get tired of coming out here in the ocean? And I said, it's amazing. Not one day is the same as another day. Never the same. The cloud, the sun, the rain, the wind, the tide, the movement. So it's never the same. So that's why I don't get tired of going to the ocean. In these protected waters, that contain more species of marine creatures than almost any place else on Earth, long lost war wrecks claimed by the power of the ocean burst with energy and life. Yawning trenches plunge into unseen depths and manta rays soar. Here, in this exotic land of the giants. I love nature, fans. 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