If a whale falls in the ocean and no one's around to see it, does it still create a complex, unique ecosystem? Turns out it does!

A "whale fall" is what happens when a whale dies out in the open ocean and its body sinks really far, to at least 1,000 meters down. Deep down in the cold, dark water there isn't much food around, so when a whale carcass shows up, all that nutritional goodness totally changes the ecosystem of the ocean floor.

The first natural whale fall ever studied was discovered accidentally by a team of scientists in 1987 during an expedition in a specially designed submarine known as a Deep Submergence Vehicle. The bacteria the team found growing on the whale bones were similar to those you'd find in places like hydrothermal vents, and they even discovered some new species of clams. So marine biologists started looking for more whale falls to study, and eventually realized that these bacteria and clams were part of a whole unique ecosystem.

It all starts with Stage One, just after the whale dies when its body reaches the ocean floor. The first scavengers to show up are creatures like sleeper sharks, hagfish, and tiny shrimp-like crustaceans called amphipods, which start to strip the flesh down to the bone. Combined, these animals can eat 40 to 60 kilograms of tissue per day, but even at that rate, it can take a few years for them to finish off something the size of a whale.

Once they've polished off most of it, it's time for Stage Two. A swarm of invertebrates moves in, bringing crustaceans, mollusks, and bristly polychaete worms-- a type of worm that's good at surviving in extreme environments like the coldest part of the ocean. They feed on anything that's left over, plus the sediment surrounding the whale, which is now packed with bits of decomposing tissue. Some of these animals have never been spotted anywhere else, like a species of snail found on that first 1987 whale fall that led to the discovery of a whole new family of aquatic snails.

After about two years, mats of bacteria colonize the whale bones, kick-starting Stage Three. These bacteria feed on lipids-- the fats and oils from the whale bones-- turning them into hydrogen sulfide gas, which would be very toxic to most forms of life, but in this case it's a key part of the whole ecosystem. All that hydrogen sulfide creates a sulphophilic, or sulfur-loving, community made up of the bacteria, the organisms that feed on them, and other scavengers that show up late to the party. An average of 185 different sulfur-loving species end up in each whale.

This stage can last for decades, 50 to 100 years, and it's a lot like some of the other strange things you'll find on the ocean floor, like hydrothermal vents and cold seeps. These vents are cracks in the ocean floor that spew hot mineral-rich stuff into the ocean, and the seeps are briny pools of liquids and gases that include lots of sulfide and methane also on the ocean floor. Since all these places provide so much potential food on the sea floor, which is otherwise pretty barren, life tends to take over.

It's kind of hard to study environments so far down though, so we're still learning about the different species found on whale bones and how they're related to those found in deep-sea vents and seeps. And it's not totally clear how the organisms that colonize a whale fall get from place to place, or how they find the carcass at all. Biologists are also trying to figure out how whaling, which could have lowered the number of whale falls, might have changed life on the sea floor.

They're working to answer these questions by studying artificially placed whale bones and other kinds of sunken biomass, like wood and kelp, to learn more about the organisms that move in. The life forms that colonize these places have had to evolve all kinds of adaptations to survive without oxygen or sunlight, surrounded by chemicals that would be toxic to anything else.

So if you want to learn more about some of the strangest examples of life on Earth, a dead whale is an excellent place to look. And SciShow is another good place to learn about weird life forms, so if you want to keep getting smarter with us, just go to youtube.com/scishow and subscribe.