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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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