Say you're Aquaman back in the early days. You're streaking through the ocean, getting to know your domain, and after a few weeks of dolphins, porpoises, whales, coral reefs and fish, fish, fish, you're growing a little bored with the same old, same old, so you dive down to the lightless depths.
Here's where things start to get really interesting. Phantasmagoric, bioluminescent creatures materialize from the murk. They would eye you with curiosity if they had eyes, but what's the point of vision down here? Luckily your Atlantean heritage grants you not only the ability to see in inky darkness (the darkest dark there is) but also to survive the bone-crushing pressure of all that water above and around you.
Attracted by movement in the distance you zoom down to one of the weirdest places on the planet — a vent in the ocean floor where the Earth's crust is splitting apart and spewing super-heated, toxic seawater from its guts. Surely nothing could live in a hellhole like this. But to your aquatic astonishment, the place is carpeted with huge tubular organisms sprouting out of the ground like gigantic, demented stalks of wheat.
Not only are these things surviving, they're thriving down here. The red plumes that top them off are waving contentedly in the ocean currents as though they couldn't have picked a better spot to settle down. And they're right. These creatures (saddled with the grotesque but evocative label, "tubeworms") are uniquely adapted to flourish in this, the most adverse of growing conditions imaginable.
Of Worms and Subs
Let's start by talking about Alvin. Not the beloved 70's toy aardvark, and not that singing chipmunk either, but the three-person, robotic-armed, deep-sea submersible that has starred in a series of spectacular discoveries on the ocean floor since the mid-1960s. Alvin's most famous find was the wreck of the Titanic back in the 1980s.
Nearly a decade earlier, in 1977, scientists were piloting Alvin around a vent in the sea floor in the neighborhood of the Galapagos Islands when they stumbled upon, or rather floated over, a field of very weird beings. They had expected to see nothing but a barren seascape. Instead, their headlights picked up a lush oasis of hitherto unseen organisms. The most prominent new species was our friend the tubeworm [source: Trivedi].
This discovery was like a bomb dropped on a whole set of biological assumptions. These creatures were living in an environment where nobody thought life was possible. At the bottom of our familiar land-dwelling food chain are photosynthetic plants that eat sunlight. So how can anything live where there's no sun?
Different world, different food chain. Instead of a photosynthetic foundation to the local diet, there's a chemosynthetic one. That means the organisms at the bottom of the food chain on the bottom of the ocean are eating chemicals. In fact, as Tim Shank, one of the leading researchers in the field of deep-sea vent life has said, the vents host the largest "chemosynthetic community" on Earth [source: Nevala]. And that community has been around for a long time. The fossil record shows that the ancestors of modern tubeworms and their vent neighbors were getting their start at the same time as the dinosaurs [source: Shank].
But the giant tubeworms aren't the only worms down there. Keeping them company are little straw-length guys called Jericho worms, bristly orange worms, wriggling benthic worms and red palm worms the size of your finger [source: Stover].
Interestingly, while there are tubeworms at vents all over the Pacific Ocean, there are none in the Atlantic where creatures like deep-sea shrimp dominate the scene. Nobody knows for sure why this is, but there are many factors that could be behind it. One theory suggests that when the Atlantic Ocean was forming, it was extremely salty, a condition that shrimp tolerate better than tubeworms. Once the shrimp were firmly established, they never let the tubeworms move in. That's because shrimp scrape the surfaces around vents for the bacteria they like to dine on, meaning they probably eat up any tubeworm larvae before they have a chance to grow [source: Shank].
Lifestyles of the Hot and Vented
One of the strangest things about the climate around deep sea vents is that the temperatures are extreme. Extremely different, that is. The water pushing out of the vents can be as hot as 752 degrees Fahrenheit (400 degrees Celsius), but just an inch (3 centimeters) away from the vent opening the water is already down to 36 degrees Fahrenheit (2 degrees Celsius). So most of the organisms living around vents have to put up with temperatures that hover just above freezing. In other words, they're not there for the nice weather. It's all about the chemical stew spewing from the vents [source: Stover].
The main chemical compound coming from the vents is hydrogen sulfide. Bacteria that colonize deep sea vents thrive on the stuff. In turn, tubeworms depend entirely on bacteria for their food — but they have no mouths and no stomachs. What they do have are massive quantities of bacteria lodged inside them — 285 billion bacteria per ounce (28 grams) of tissue, in fact. Actually, beyond its bacterial chums, there's not much to your typical giant tubeworm besides an aorta and some gonads encased in a 4- to 6-foot-long (1.2 to 1.8-meter) white tube rooted in the ocean floor [source: Trivedi].
Tubeworms are decked out with red plumes on top, but they're not just for looks. The plumes are red because they're full of blood. The hemoglobin in the blood binds to the hydrogen sulfide floating by and moves it down into the tube where bacteria oxidize it and produce the carbon compounds the tubeworms need to live. The tubeworms and their bacteria live in a completely symbiotic relationship, each benefiting from the other [source: Stover].
The only problem is that vents don't vent forever. They can switch on or off suddenly without any notice. And when they switch off, the flow of hydrogen sulfide stops, which means all the organisms in the environs die. And since the vents are isolated from one another like undersea islands, the big question is: How do those tubeworms manage to colonize the next vent that appears far away across the seafloor?
Since the discovery of tubeworms in 1977, scientists have been scratching their heads about vent colonization. After all, these tubeworms have specifically adapted to a highly specialized environment that has the capricious quality of switching on and off at random. And, to add another layer of difficulty to tubeworm propagation, the vents are little oases on the vast desert of the seafloor. How do organisms that are rooted to the ground spread to another vent that might be more than 50 miles (80 kilometers) away?
After much intensive and inventive research, scientists are closing in on an answer. To start with, it's important to know how tubeworms make babies. That part is easy: They do it the same way shellfish do, by unleashing eggs and sperm into the water. The sperm bump into the eggs and combine to form larvae. The larvae drift on the currents like dandelion spores on the wind, until they come to rest, hopefully on a hospitable spot suited to their highly specific needs — i.e., a vent.
Here's where things get interesting: It turns out that those larvae are born with a ton of energy. Not rambunctious-toddler energy, but stored energy in the form of lipids. In fact, they've got enough of the stuff to last for 40 days.
But still, within that 40-day allotment, how do those larvae get from point A to point B? Researchers had to be creative because trying to keep track of thousands of microscopic specks in the pitch darkness of the deep sea is no joke. They started by building computer models of the currents and then releasing virtual larvae into those currents. Once they had some interesting results, they dumped a harmless, trackable chemical compound near a vent and watched what happened.
They soon discovered that the currents around a vent can carry the little tubeworms-to-be along the mid-ocean ridges where vents are found. Even if the currents eddy and veer off course, they can still swing back and drop their passengers in hospitable vent territory where they can happily grow to full tubeworm adulthood [source: Villano].
Mysteries of the Vents
Historically, how could tubeworms and their other vent colleagues have spread to vents that were more radically isolated from each other? It turns out, there might be some handy stepping stones between vents that are more widely dispersed.
Have you ever caught yourself idly wondering, just what happens to whales when they die? Well, it turns out that there's something called a "whale fall," which refers to a dead whale sinking down to the bottom of the ocean. There, it becomes food. A lot of food. The microbes that tuck into the whale's soft tissue produce hydrogen sulfide. Sound familiar? That's the stuff those vent bacteria love to feast on. And the bacteria like to live in symbiotic bliss with tubeworms. In fact, studies have shown that whale falls have 10 species in common with vents [source: Shank]. Two of them are miniature versions of the giant vent tubeworms to which they're related. These little worms also live symbiotically with bacteria, and it appears they co-evolved with whales over the past 40 million years [source: MBARI].
Another stepping stone for chemosynthetic deep-sea fauna like tubeworms may be something called "seeps." These are areas in shallower waters where methane and hydrogen sulfide seep from the ocean floor, supporting a variety of chemosynthetic species. The tubeworms that live at seeps aren't the same as the ones that cluster around vents, but they share enough in common to make some researchers theorize that species could migrate back and forth between seeps and vents.
In the past few centuries, yet another stepping stone has been introduced: shipwrecks. As the wood from old shipwrecks decays, it produces the chemical nutrients those marine bacteria crave.
Taken together, whale falls, seeps and shipwrecks might help to explain how deep-sea critters like tubeworms survive and disperse themselves across the vast tracts of the ocean floor.
Author's Note: How Volcano Vent Tubeworms Work
I'll confess that until researching this article I never gave tubeworms a second thought. Now that I've given them a second, third and fourth thought, I'm intrigued. There's something oddly reassuring about the existence of creatures that can live without sunlight and under crushing pressure while thriving on chemical compounds that would be toxic to most organisms. Come the robot/zombie/nuclear/environmental apocalypse when all life on Earth appears to be wiped out, those tubeworms and their ilk will still be down there enjoying the weird world of deep-sea vents oblivious to our travails topside.
More Great Links
- Monterey Bay Aquarium Research Institute. "Whale carcass yields bone-devouring worms." MBARI Press Room. July 29, 2015. (June 22, 2015) http://www.mbari.org/news/news_releases/2004/whalefall.html
- Nevala, Amy. "Settling on the Seafloor." Oceanus Magazine. July 8, 2005. (June 18, 2015) http://www.whoi.edu/oceanus/viewArticle.do?id=5367
- Shank, Timothy. "The Evolutionary Puzzle of Seafloor Life." Oceanus Magazine. March 22, 2004. (June 18, 2015) http://www.whoi.edu/oceanus/viewArticle.do?id=2505
- Stover, Dawn. "Creatures of the Thermal Vents." Smithsonian. (June 11, 2015) http://seawifs.gsfc.nasa.gov/OCEAN_PLANET/HTML/ps_vents.html
- Trivedi, Bijal P. "Giant Tubeworms Probed for Clues to Survival." National Geographic Today. Oct. 28, 2002. (June 11, 2015) http://news.nationalgeographic.com/news/2002/10/1028_021028_TVtubeworm.html
- Villano, Matt. "The Mysterious Movements of Deep-Sea Larvae." Oceanus Magazine. Dec. 31, 2009. (June 20, 2015) http://www.whoi.edu/oceanus/feature/the-mysterious-movements-of-deep-sea-larvae