Thanks to Linode Cloud Computing for  supporting this episode of SciShow.

You can go to linode.com/scishow to learn more and get a $100 60-day credit  on a new Linode account. [♪ INTRO] If you’ve ever found yourself in an  aquarium or at a tide pool on the beach, you’ve likely come across a sea urchin, one of those spiky round creatures  that sometimes hang out on the shore. And if so, maybe you’ve noticed  that they like to cover themselves in all sorts of odds and ends, like bits  of shell, algae, small rocks… even trash.

Urchins that live in home aquariums  will even wear little hats that people 3d-print print for them,  which of course is a thing that people do. Over the years, several studies  have looked at why urchins bother picking things up off the  seafloor and putting them on. And the answer seems to depend  on the species of urchin and the environment they inhabit.

Out in the tropics, the so-called collector  urchin may be protecting itself from the Sun. These urchins can be found in  the shallow waters off Hawaii, the Indo-Pacific, and the Bahamas, where  they’re exposed to a lot of sunlight. And in a 2016 study, one  researcher tested a hypothesis that they were picking up items for UV protection.

They put a group of urchins in both  high- and low-light conditions, and offered them small plastic squares  that came in either clear and red. They found that in settings with high  light, urchins chose to cover themselves with more red pieces, which gave them  the most protection from UV light. It’s kind of like how you might trade your  daily SPF lotion for a heavy-duty sunblock if you’re spending all day in the sun.

And maybe wear a big floppy hat! Meanwhile, researchers think that the  green sea urchin uses its adornments to weigh itself down. This species tends to live in shallow  waters in the northern Atlantic and Pacific Oceans, where it  sometimes gets battered by waves.

Wherever there’s lots of wave activity,  the urchin heavily covers the top and sides of its body with whatever it can find, which helps make it heavy enough  to avoid getting swept away. And further south, Antarctic urchins  have been found to cover themselves as a way to avoid predation. Their main predators are king crabs  and sea anemones, and researchers found that they were more likely to put on  coverings when more predators were around.

In a lab experiment, another species  of urchin was more likely to survive being exposed to a predator if it  was given shells to cover itself. So basically, these decorations  may be a type of camouflage to keep urchins from being found and eaten. And finally, the kina, a large  urchin found in New Zealand, may use the items it collects as a source of food.

Researchers found that this species  was covering itself even in the dark, suggesting that it wasn’t trying  to protect itself from sunlight. And its predators don’t rely on sight to find  prey, so camouflaging itself would be pointless. But a field study of these urchins  found that they were carrying algae. or stuff with algae attached –  specifically, a kind they rely on for food.

So, it seems like they’re basically  carrying around their own little pantry. Being able to capture food and tote it  around is pretty handy, especially for these urchins, which may not always have  lots of algae around for grazing. As of now, researchers are still exploring how and why urchins dress  themselves in seafloor debris.

But all in all, they can agree that while  various species have many different habits for different reasons, these  could all be examples of tool use, though that definition depends on who you ask. So, even though urchins are  probably interested in fashion, these spiky residents of the seafloor are  still pretty smart… and smartly dressed! And talking about fashion-forward  sea urchins just wouldn’t be the same without videos like this one to show them off.

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