Deep in the Indian Ocean, sunlight disappears and life gets... weird.
Hydrothermal vents are openings on the ocean floor that reach down below the surface of the Earth's crust. The heat and minerals from inside the crust come pouring out of the vents like a chimney. The water surrounding the vents are filled with intense heat and "smoke" that is full of toxic compounds and minerals. It sounds like a terrible place to live! Instead, scientists have found tube worms, heat-loving crabs, and other extremophiles that never see daylight living happily by these vents.
In 2001, a submersible ocean craft dove twenty-six hundred meters (8,500 feet) into that inky darkness to reach an underwater sea vent. Scientists thought this would be just another vent, but they were in for a huge surprise. They discovered a snail covered in living metal armor!
Meet the scaly foot gastropod (AKA the "volcano snail" or Chrysomallon squamiferum). It's covered in parts that absorb iron from the environment. The shell is coated with iron, and the soft foot is covered in hard flaps called sclerites that are also made with iron. Scientists were shocked! This is the only known living creature in the world to have this ability to blend metal into its body parts.
Most organisms have iron within their body. For humans, iron is an important mineral in our diet and our red blood cells would not carry oxygen properly without it. The scaly foot gastropod is different, though.
There are bacteria living inside of a large gland next to the gastropod's esophagus. These bacteria use chemosynthesis (like photosynthesis, but with chemicals instead of light) to turn materials like iron and hydrogen sulfide into nutrients for the gastropod. The snail itself doesn't "eat" anything; it's just fed by its bacteria buddies. A true symbiotic relationship! 🤝
Scientists aren't exactly sure how the iron gets built into the snail's shell and sclerites. One theory is that the snails absorb iron directly from the water around the vent . If that were true, though, we would expect other extremophiles in the area to soak up the iron, too. Another theory is that the bacteria inside the gastropod make iron sulfide minerals as waste that accumulates in the snail's body, but we don't know how that iron ends up being useful to the snail instead of just killing it. The science world is still pondering these unanswered questions.
So far, volcano snails have only been found near a few vents of the Indian Ocean. Scientists are realizing that each hydrothermal vent can have a unique combination of properties. For example, the graphs below show data from vents in shallow water near Kueishantao Island, AKA Turtle Island:
Here are a couple of questions I think of when I look at this graph:
💡Cell abundance is a measure of how much life is found around the vent. Scientists collect seawater samples and look for tiny organisms inside. What do you notice is different about the cell abundance of vent C, and can you see any potential reasons for this difference from other vents? How could scientists test these reasons?
💡Imagine you are a scientist diving around Turtle Island to explore these vents. Write a story where you find one vent, describe everything you notice, and then discover a different vent and describe it how it compares.