If you’ve ever gone beachcombing, you’ve probably noticed how skittish crabs are. These little critters are pretty common in tide pools and under rocks, but you can often only catch quick glimpses of them before they’ve burrowed, withdrawn into shells, or otherwise hidden. That being said, I was thinking about the differences between hermit crabs and “regular” (shell-less) crabs and came up with an interesting question: are hermit crabs, who carry shelter around with them, braver than regular crabs (also called true crabs)? They don’t have to scurry away under rocks because they have their shell, so perhaps they’d be willing to take bigger risks. This idea became the foundation of my independent project, which I’ll talk about more below.

              My project was made up of two experiments. The first experiment involved putting crabs in a container with food on one side (in an exposed area) and a rock on the other, then waiting for 3 minutes to see if the crabs would start eating the food. With each trial I switched between using a hermit crab and a true crab. After analyzing my data, I turned up no significant relationship between the type of crab and their likelihood of feeding.

              My second experiment involved a similar setup, but with a foreign object at one side of the tank and no rock. The goal was to see how willing the crabs were to investigate an unknown object, and if hermit crabs were more likely to investigate it than true crabs. I didn’t use a rock because I noticed in the first experiment that the crabs treated the walls as shelter, so I decided that was enough. The foreign object was a pink aquarium rock, and I switched between two sizes. Much like the first experiment, after analysis I found that one crab type was not significantly more likely to investigate the object than the other.

              So at the end of the day, I wasn’t able to find any significant differences between hermit crabs and true crabs. What does this mean? Well, maybe hermit crabs and true crabs are actually equally brave (or not brave). When you think about it, this might make sense considering lots of predators have found ways of cracking into shells. If hermit crabs and true crabs are equally vulnerable, then they’re likely to be equally skittish. It’s also possible that a different test would reveal the difference I was looking for. For example, I noticed that the hermit crabs tended to explore their environment more than true crabs. A test that measured the amount of a habitat that the crabs explored could reveal something interesting. Maybe crabs don’t have a knight’s bravery, but perhaps hermits are adventurous at heart?

Looking for more interesting info about crabs? Check out this awesome video about how hermit crabs work together to change shells: Hermit Crabs LINE UP To Swap Shells! | Life Story | BBC Earth Kids – YouTube. Or, you could read this paper about crab smelling by Waldrop (2013): https://doi.org/10.1093/chemse/bjt024

              In the remote town of Bamfield, B.C., a group of scientists and UBC students (who were tagging along digitally through zoom) performed a dredge of the ocean bottom and what they found will shock you! What wonders, or horrors, did they uncover from the depths? Read on to learn about some of these mysteries yourself!

The elusive decorator crab

              While it may not look like it, the picture above is in fact a crab. These masters of disguise are called decorator crabs, so named because of how they decorate themselves with whatever is around them. This can let them hide in plain sight by sticking pieces of their surroundings to themselves, but they can also choose a different path with their decoration…

              Rather than simply hiding, this crab has taken to the offensive by decorating itself with small anemones. This way, it uses the anemone’s stinging ability as a form of predator deterrence. Why evolve stinging cells when you can just use your neighbor’s?

Nature’s tanks: the chitons

              Another organism that was found was the chiton. Chitons are a part of Mollusca, a large group of animals that includes some organisms with shells like clams and snails, as well as shell-less animals like octopuses and slugs. Among the mollusks with shells, chitons are recognizable for their shell that is composed of plates, like plates of armor. This gives their shell some flexibility, so the chiton can bend while still being protected.

Voracious predators of the ocean: sea stars

              The dredge also turned up numerous species of sea stars. These seemingly simple animals are in fact quite weird and wonderful! They have a complex system of water-filled tubing that connects to each of their numerous tube feet, which generate suction power using hydraulics. Sea stars are also formidable predators, eating a wide variety of different things depending on the species. They feed by ejecting their stomach onto their prey, digesting them outside their body, then sucking up all the digested nutrients. While we find them interesting and cool, they are terrors of the sea for their prey!

              You may have also heard of sea stars over the past few years because of their mysterious decline in numbers. Sea stars of many species have been suffering from Sea Star Wasting Disease (SSWD), a poorly understood phenomenon that is causing mass fatalities of sea stars. Sun stars, an example of which is shown above, have been particularly affected. A few were found in the dredge, but they were much smaller in size than those that used to be found.

              Want to learn more about some of these creatures of the deep? Check out this video on SSWD: https://www.youtube.com/watch?v=ISY3Ebeq5jk or Sanka et al.’s 2016 paper on decorator crab morphology and how it contributes to their decorative abilities: https://doi.org/10.1016/j.actbio.2016.05.021.

Have you ever been walking along the beach, seen a little crab scurry under a rock, and wondered: how would that crab react to a really loud Katy Perry song? Because we have! In all seriousness, we spent our lab last week running all sorts of interesting experiments with crabs (yes, including the Katy Perry thing).

The crabs we studied were of the species Hemigrapsus oregonensis. These little critters are common on beaches along the west coast of North America and eat pretty much anything that they can get their claws on: algae, plankton, even smaller crabs. It really is a crab-eat-crab world out there! Our class was split into groups to investigate different aspects of these crabs. For example, one group looked at what factors affect aggression in these crabs by putting them in a series of wrestling-style cage-matches (okay not really, the most aggressive the crabs got was poking each other).

My group decided to investigate whether these crabs would respond to the sound of bird calls. Birds are known to take advantage of low tides by eating exposed crabs. While crabs tend to hide at the first sign of danger, are they able to hear and recognize the sound of their foe? To spice up our experiment, we also measured their response to “Roar”, by Katy Perry.

Unfortunately, we didn’t end up finding any significant trends. It seems that the crabs either don’t count on their hearing, or we needed to do more tests to get a better idea of what was going on. Funnily enough though, several group members noticed that the crabs tended to respond to Katy Perry. While the crabs didn’t care about a mighty seagull roar, apparently they took notice of Katy Perry’s “Roar” (see what I did there?). You’d think that they would be afraid of the music, seeing as it’s probably just a loud noise to them. However, instead of running away from the source of the music, they seemed to run toward it! So, while my group didn’t find any scientifically significant facts, we did find out one important detail: shore crabs appear to be Katy Perry fans. If that’s not hard-hitting science then I don’t know what is.

Interested in learning more about Hemigrapsus oregonensis? Check out this video of one feeding: https://www.youtube.com/watch?v=D2PHyOjIzLI. If you want something a little more science-y, try reading Waldrop’s 2013 paper on crab smelling (https://doi.org/10.1093/chemse/bjt024) or Jensen and Egnotovich’s 2015 paper on crab colouration (https://doi.org/10.1093/czoolo/61.4.729).