This episode is sponsored by Squarespace.

Go to Squarespace.com/microcosmos to save 10%  off your first purchase of a website or domain Every time we see diatoms, we have to give  it to them: they’re just simply stunning. They’re single-celled and major  producers of the oxygen we breathe,   but the real reason we love seeing  them is because of their frustules— those silica shells they construct  for themselves to live in.

They’re architects building stained glass  walls to float in, and the effect is beautiful. But apparently, diatoms are not content  to rest on their ornate laurels. Because some don’t just  construct a home for themselves.

They construct a much larger structure  that houses a whole gathering of diatoms,   an apartment building made of one long tube. Yes, a tube. They’re really striking to look at, like pieces  of hay or strands of hair braided together.

The tubes we’re looking at  right now come from Iceland. Our master of microscopes James sent his  assistant Ela there on a microbe hunt,   collecting samples from a  bunch of different places. But they saved the marine samples for last because   those organisms tend to be  more delicate to handle.

So on this last collecting session,   James was on a video call, watching as  Ela scanned the dock she was standing on. And along the submerged parts of the dock,   James spotted tufts of brownish  stuff peeking out as the waves broke. So he asked Ela to grab some and bring them back.

The next day, she arrived at 6 am  and crashed on the couch, while James   immediately grabbed the samples to take a look.  And apparently, the entire time, he was saying, “This is so beautiful.” The samples that Ela brought back from  the dock were teeming with diatoms. It might seem surprising that the waters  of Iceland can bring forth so much life,   especially during the cold and dark winter months. But this matches James’ experience with the  ponds in Poland he gathers samples from,   which often end up dominated  by diatoms during the winter— even as green algae numbers drop.

Diatoms seem to be fairly hardy in the dark. One study found that diatoms survive longer than  flagellates in extended periods of darkness. The researchers didn’t find a specific reason why  they’re able to tolerate the dark for so long, but   they theorized that perhaps the diatoms were more  conservative in how they managed energy reserves.

Others have also suggested that their  survival may be due to oils stored in   the diatoms, which may keep them better  stocked compared to other organisms. Their survival in winter means  that when spring rolls around,   diatoms are often the first  groups to bloom in polar waters. And perhaps these tube-like  structures are part of their success.

They’re not found as often in warmer waters,  but things are different when it gets cold. In 1994, a scientist found a whole bunch of  these tubes along the Dutch coast in late winter. And by a whole bunch, I mean there were more than   10 billion diatom cells living  in tubes, per square meter.

These tubular colonies start with  one diatom secreting a thread of   mucus from a pore, which it weaves into a tube. Living in a mucus tube might not have  the same romantic feel as the diatom’s   stained glass shells, but diatoms  don’t have much need for romance. As the tube gets longer and longer, the cell  reproduces asexually, dividing and populating   the tube with more cells like it so they can  travel through their shared home and add to it.

With every cell, a new roommate  and construction worker is added,   a cell that can strengthen and add  to the tube by producing more mucus. At times, the cells might reproduce  faster than the tube can expand,   at which point they might start  to create a little side tunnel. Their tube is a colony, and they  might end up attached to surfaces   like sand particles, or a submerged Iceland dock.

And they’re kind of similar to  colonies we’ve seen on this channel,   like Volvox and their spherical gatherings. One thing that’s strange though is that based  on what little we know about these tubes,   it doesn’t seem as if these diatoms  do much to coordinate their activity. This is different from volvox, where  various cells take on different functions,   and they work together to create  a better life for everyone.

But some of these diatoms act like they’ve  constructed a crowded city street just to   ignore each other, a group of co-workers who  don’t even say hi to each other in the hallway. They’re little independent entities,  countless ships passing in the night. And for those living in narrower  tubes, there’s no movement at all.

They’re simply stuck in place, next to  a family member they don’t acknowledge. But there must be a reason they  live together in these tubes. Otherwise, why bother with the time and  energy it takes to start making a tube,   and to keep adding to it.

The tube might be a form of protection,   making the diatoms too big for  microbial predators to consume. But it’s probably also a way to help the diatoms  access light through a few different mechanisms. To start, the tubes help lift the diatoms away  from the substrate they might have sunk to,   raising them towards any light  that might penetrate the water.

And as they float in the water,  the tubes allow the diatoms to   move with the rhythm of the waves,  illuminating all sides in the process. At least, that’s one of the possibilities  for why these diatoms turn to tubes. But stepping back from the “why,” it’s like  we’re starting to see more of who diatoms are.

They’re builders. They may never have set out to become that,   but their approach to the world around  them has been to build, to assemble. To make something functional and beautiful  even if the beauty is not the point.

Thank you for coming on this journey with us as  we explore the unseen world that surrounds us. And thank you to Squarespace  for sponsoring this episode. Squarespace gives people a powerful and   beautiful online platform from  which to create their website.

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