Scientists dropped a camera into an active underwater volcano... sharks were living inside

This episode is brought to you by GiveWell.org. Go to GiveWell.org and enter Real Science at checkout to have your donation matched up to $100. In the Pacific Ocean is a region that's been almost impossible to study, a region so dangerous, for many years, scientists didn't dare venture there, a place with nearly continuous volcanic eruptions. Kavachi volcano in the Solomon Islands is one of the most active underwater volcanoes in the world. It sits just 20 meters below the surface, and its base lies on the seafloor at a depth of 1.2 kilometers. Beyond this, little was known about this volcano for the centuries it's been known to exist. That is, until 2015, when a rare lull in volcanic activity allowed researchers to get close to its active crater and flanks for the first time. Using a combination of underwater cameras, recording devices, and scuba divers, the team collected a huge amount of information, even though it meant taking a few risks. Although the volcano wasn't actively erupting, gas still bubbled wildly from around the rim, which could cause caustic burns if the divers got too close. The team had to listen carefully to the water for the telltale rumble that comes along with eruptions. just in case Covache suddenly unleashed its fury once more. But what they found was worth the danger. Not only did they get bacterial and rock samples, but their baited cameras also captured some incredible sights. There were zooplankton and larvae, as the scientists expected, but also something completely surprising. Schools of fish like bluefin trevally and snapper, silky sharks and hammerhead sharks were all seen inside the crater. The water temperature above the crater was more than 13 degrees Celsius higher than the surrounding ocean, growing as warm as 29 degrees Celsius. What's more, the hydrothermal vents were still releasing concentrated amounts of carbon dioxide and sulfur dioxide, which makes the water much more acidic than normal. And yet, this vast array of life forms was still living in and around the mouth of the volcano. How are these creatures all surviving such an inhospitable environment? And what can they tell us about the future of our oceans? Kavachi is a fascinating example of submarine volcanoes, but it's only a tiny window into a vast underwater realm. Of Earth's 1,500 active volcanoes, the vast majority are found in the ocean. Some are the result of plate tectonics, plates pulling apart or smashing into each other. Other volcanoes come from hot spots, which form not from tectonic plates, but from abnormally hot areas of magma that burst through. And erupting volcanoes are only a small part of the geothermal activity happening on the seafloor. There are also hydrothermal vents, which form when water seeps into the broken crust, gets superheated up to 400 degrees Celsius, and shoots back into the ocean filled with chemicals and minerals. Cold seeps occur in similarly volcanic places, but the water doesn't heat up. Instead, sulfide, methane, hydrogen, and hydrocarbon-rich fluids leak into the ocean, often for longer than hydrothermal vents. And then there are the megaplumes, which are like hydrothermal vents on steroids. These brief but enormous bursts of hot, mineral-rich water are still baffling to scientists because they're so hard to observe. But it's clear they have immense consequences for surrounding ocean water chemistry, since a single megaplume can discharge more than 100 cubic kilometers of water in one go, the equivalent of 40 million Olympic-sized swimming pools. As for Kawachi, it's located on the Pacific tectonic plate, only 30 kilometers northeast of the boundary with the Australian plate. It's released huge quantities of steam, ash, and glowing bombs of lava on multiple occasions. It's even produced ephemeral islands up to a kilometer long over the course of its explosive activity, making it a very dangerous object of study. And all of this volcanic activity in Earth's oceans has had an enormous impact on the seafloor. Even long-extinct volcanoes have left traces on the underwater topography. The rugged hills and mountains created by volcanic activity are called seamounts, and they cover more than 28.8 million square kilometers, an area larger than any terrestrial habitat. Some of them are in the deepest, darkest parts of the ocean, while others come all the way up to warm, shallow seas. Scientists think around 45,000 seamounts exist all over the world, but we've explored fewer than 200 of them. In other words, we've seen less than 1% of what might be some of the most unique habitats on our planet. While researchers stumbled upon the first seamount back in the late 1800s, it wasn't until the 1970s that we first saw hydrothermal vents and the bizarre creatures living around them. In 1977, a team of 30 geochemists, geophysicists, and marine geologists came together to study the Galapagos Rift. No marine biologists were included because everyone assumed there would be no life to see. As they dropped their cameras down 2,500 meters below the surface, the researchers were surprised to see what looked like signs of heat. And then, to their shock, something even more unexpected came into view. what looked like alien life forms. Foot-long pale crabs, red-headed tube worms the size of a full-grown human, clustered tightly around steaming pillars. They had discovered hydrothermal vents and the baffling ecosystem they support. From that point on, scientists employed a vast array of technologies to continue exploring these underwater geysers. There's the Lost City hydrothermal field in the Atlantic Ocean, whose vent structures grow as tall as the Leaning Tower of Pisa and come from peridotite rock instead of basaltic rock, which makes up most of the ocean floor. This means the chemicals coming out of the vents around the Lost City have a much different composition than in other locations, and yet they still support life. In fact, scientists have found around 800 vent animal species and countless microbial species, with many more likely to be discovered as we continue exploring the deep ocean. In addition to the tube worms and crabs scientists first saw in the 70s, we now know there are also giant mussels, shrimp, and perhaps the most important organisms of all, microbes, that survive alongside the vents. These microbes make up the entire base of this strange food chain, and they do it in a place where there's no sunlight at all for photosynthesis. Instead, the microbes convert inorganic compounds like hydrogen gas, sulfur, methane, or iron into nutrients. This allows the microbes to thrive in what would otherwise seem like hellish environments and support many other organisms as well. These microbes help explain the surprising amount of life around Kavachi. The researchers found bacteria related to Sulphurimonas, which use chemosynthesis on sulfur and carbon dioxide to produce energy. Filter feeders like krill and clams can survive entirely on these bacteria, and those populations in turn can support bigger fish and even sharks. It's all part of a vast volcano-based food web, and it happens all around the ocean in different environments. Take the giant red-tipped tube worms, for example. They have no mouths or digestive tract, instead relying on their on chemosynthetic microbes hosted inside their body to provide them with energy. Or there's the vent shrimp, which has a symbiotic relationship with chemosynthetic bacteria living in its gill chambers. It seems that the shrimp gets some kind of nutrients from the bacteria, and the bacteria benefit from the shrimp being able to get close to the vent systems where the highest quantities of chemicals are pouring out. And the life forms populating these volcanic settings don't stop there. Around Kickem Jenny, the most active submarine volcano in the Lesser Antilles of the Caribbean, researchers found what they believe to be the largest mussel shell ever sampled. One bathymodiolus boomerang measured 36.6 centimeters long, bigger than a foot-long sub. And near one seamount in Samoa, a growing volcanic cone named Nafanua supports a thriving population of eels around its summit vent. They feed on shrimp and seem capable of surviving the hydrothermal emissions, even though other fish are killed by them. And that is one very big problem with all these volcanically active sites. There's a big risk of getting burned, poisoned, or caught up in an explosion. While most of the seamounts around the world are made from extinct volcanoes, there are still hundreds of active volcanoes erupting on a regular basis. And when those eruptions happen, they can be disastrous for marine life. In 2011, for example, a submarine volcano near the island of El Hierro triggered more than 10,000 earthquakes on land and led to vast numbers of dead fish floating on the ocean surface. The ocean temperature increased nearly 19 degrees Celsius around the volcano crater. Carbon dioxide caused the water to be much more acidic. and in some areas, the water was almost completely void of dissolved oxygen. The debris created by the eruptions also made the water much cloudier than normal. Scientists found that the upper limit of light penetration was 100 meters shallower than normal, which can have a big effect on plankton communities and other organisms living in the mesopelagic. In other cases, submarine volcanoes unleashing gouts of lava have killed deep-sea fish, which then float to the surface, sometimes teaching us about fish we never knew existed. But it means that even those organisms that may be benefiting from hydrothermal vents can be killed if the volcanoes become more eruptive. And if there's enough volcanic activity happening all at once, it can have profound consequences on ocean life. Researchers point to the Cenomanian-Turonian event that happened around 90 million years ago and led to the extinction of almost a third of marine invertebrate species. That sudden collapse of ocean life is thought to be largely the result of high levels of hydrothermal activity, making the ocean too warm and too acidic. That said, huge eruptions can have a positive effect, namely on phytoplankton populations. Just this year, the largest submarine eruption of the past century occurred in the South Pacific Ocean. The Hunga Tonga volcano erupted in January and was so massive that its plume of ash reached 58 kilometers in altitude. The blast was so loud that it could be heard in Alaska, nearly 10,000 kilometers away, and it triggered a massive tsunami wave. But that enormous eruption also triggered a huge phytoplankton bloom that could be seen by satellites. Scientists have hypothesized that these oxygen-producing microbes had a sudden boom because of the ash and nutrients released by the volcano. The effects of underwater volcanism are clearly a mixed bag for ocean life. which raises the question of how the sharks and fish swimming around Kavachi are able to deal with the chemical changes to the water and the threat of another eruption. And it's still an open question. There are a lot of logistical challenges for researchers trying to get out to such remote locations, let alone avoid having an eruption occur right underneath them. But these issues are well worth researching because they could tell us a lot about how marine life will respond to climate change. As more carbon dioxide enters the atmosphere, the oceans will become more acidic, affecting shell builders and other invertebrates. And as the temperatures rise, marine heat waves are becoming more common and threatening coral reefs as well as fish. So the better we understand how life survives around hydrothermal vents and underwater volcanoes, the more we might be able to do to protect threatened species and help them adapt. And maybe we'll uncover a few more sharkcanoes along the way. My mission with these videos is to inspire people to love the natural world and to show that through methodical science, we can improve the state of things. 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And if you're looking for something else to watch right now, you should watch our latest video about the insane biology of sperm whales. Or watch Real Engineering's latest video about Helion and the new way to achieve nuclear fusion.