I found my true calling; coaxing hermit crabs out of their shells (in the name of science of course).

This week our class’s lab was the perfect example of how a seemingly serious (and important) topic in science, can quickly become a platform for what I call “scientific tom foolery”, given the right people and the right study animal. Of course, what do you expect when you give a class of marine invertebrate nerds to chance to play with hermit crabs….

Our lab started out strong and serious, as we began with a lecture on how climate change. As carbon dioxide (and other green house gases) increases in our atmosphere, sea water will consequently change too and expose marine life to new living conditions. We discussed the widely distributed and sever coral “bleaching” events, where corals under high temperature, lose their ability to harvest light energy, leaving only their white (bleached) skeletons. When scientists first started studying how marine invertebrates may respond to climate change, the main environmental condition they were investigating was temperature. However, now researchers investigate how multiple environmental conditions work together and invoke a stress response in marine invertebrates (multiple stressors). For example, how do invertebrates deal with raised temperature, lowered salinity, and a combination of the two?

We decided to run our own “multiple stressors” experiment on the charismatic marine invertebrate, the hermit crab (pictured below). Instead of spending energy on growing their own shell, hermit crabs are “naked”, but steal empty snail shells and tuck their backsides into them for protection.  We chose to see how hermit crabs respond under temperature and salinity stress, and whether one stressor has a larger effect than the other. We expose these crabs to tanks of high salinity + low temperature (our control treatment) and compared them to crabs in tanks of high salinity or high temperature, and a tank with both high temperature and low salintiy (the multiple stressor treatment).

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A typical sized hermit crab of the species Pagurus hirsutiusculus in its borrowed shell.  Photo  credit: wikimedia.org

We needed a behaviour to compare between our treatment tanks, and one of the responses we measured was how long it took the crabs to find their shell after being removed from it. Now this is where the “scientific tom foolery” comes in to play, as the serious side of science teams up with the goofy side of experimenting on invertebrates.

We started by holding the crab upside down by its shell. This worked for some crabs but for more stubborn crabs, we had to get creative. Eventually we started shaking the crabs out of their shells (the crabs might have not been too keen on that, but that’s why it worked!). For some we had to hold them out of the water, with their claws just touching the water surface, coaxing the crabs to leave their shells willingly. One crab had a longer shell and was not willing to part with its prized possession. I tried my proficient techniques but this one required some thing bigger and better. This is where Doctor Harley had to step in with his decade long skill set of mastering the hermit crab removal. With the combination of heat stress via a table lamp, and a couple pokes, but we finally got the sucker out (pictures below)! Turns out it takes more than just a bachelor degree to master the hermit crab removal.


Our tricky hermit crab after we finally pull it from its prized shell. 

For more information of coral bleaching and multiple stressor studies, check out the work being done at The ARC Center: https://www.coralcoe.org.au/

and give this article a read for further information: http://www.academia.edu/4869207/Evidence_for_multiple_stressor_interactions_and_effects_on_coral_reefs

The Socialite Hermit Crab

I suggest a name change for “hermit” crabs to be changed to “socialite” crabs, and here’s why:

As a hermit crab’s body grows, it will outgrow its current shell and must go on an expedition to find a new bigger shell. This leads to an incredible process called the “Shell Exchange”.

A hermit crab will set out in hopes of finding that new perfect shell: not too big, not too small, but just right. Once it stumbles across a vacant shell, it will leave its current shell to go inspect the size of the new one. If it happens to be too big, instead of continuing the search for that perfect sized shell, it will simply return back to its original shell and take a snooze. Slowly over the course of the day or night, other hermit crabs from far and wide will join together around the vacant shell, socializing and passing time. At some point, the crabs form a conga line, ordered from largest to smallest, patiently waiting for the one hermit crab who will set everything into action. Once a hermit crab comes along who finds the large vacant shell to be just the right size, he will claim it leaving behind his slightly smaller shell. All the crabs in the conga line now exchange shells in sequence, leaving every crab with a perfectly sized shell!
Check out this amazing Shell Exchange in action at : https://www.youtube.com/watch?v=f1dnocPQXDQ

Hermit crabs have these shell exchange gatherings many times throughout their lives, making me believe their name should really be “socialite” crabs rather than “hermit crabs!

The only other time you might see a hermit crab out of its shell is when it feels threatened.

Hermit crabs rely tremendously on their shells for protection, as the core of their bodies are soft, unlike most of their crustacean relatives. This can lead to vigorous competition between hermit crabs because vacant shells tend to be very limited. This ends up leaving many hermit crabs with shells too small for their body size. If these hermit crabs sense predators, they are not able to retract back into their shells and therefore will abandon their shells temporarily to find better refuge.

This past week in the Biology of Invertebrates lab we worked with hairy hermit crabs to see how long it would take for the crabs to re-enter their shells once taken out. We did this by removing the crab from its shell, then placing both the crab and its shell into a small tank and timed how long until the crab re-entered its shell. My group found that the crabs felt very naked and afraid without their shells, and as soon as they found their shell in the tank they would immediately crawl back into it, as shown below:


Hermit crab re-entering its shell after being removed. 

If you have fallen in love as much as I have with these cute and clever invertebrates and want to learn more about them, check out this BBC page full of information on the “socialite” hermit crab ! 




Harry, the Hairy Hermit Crab

Say hello to Harry the hairy hermit crab (Pagurus hirsutiusculus).   Common to the intertidal zones of Alaska to California, as well as South Japan, these little guys are a friendly face you’ll be sure to encounter on the West Coast at some point or another.  In our lab we did 3 different experiments with them – but first, here are some quick facts to get to know our hairy pals before explaining our experiments:

  • They’re distinguishable by white stripes on their legs and antennae, as well as being covered in hair.
  • They’re opportunistic feeders, so they’ll pretty much eat whatever is around: detritus, seaweed, meat, etc.
  • They use the abandoned shells of other gastropods (mostly sea snails) as protection from predators. They’ll leave this shell either after growing too big for it and wanting a more spacious abode, or as an escape tactic from predators.
  • They have 2 antennules that they constantly flick in the water to smell different odours.
  • The right claw is bigger than the left and is mainly used for defence.  The left one is used for more delicate motor skills like eating or getting in a new shell and has special hairs (setae) on it that can tell what shell would make a good home.  See here for more info on how they choose shells.
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See the white bands?

To get a little more acquainted with Pagurus we did 3 experiments to see how some of their basic behavioral traits change hermit crabs kept in different temperatures and salinity levels.


First, we counted how many flicks the hermit crabs made in 30 seconds – which is easier said than done because those buggers move fast.  Here’s an even closer look of a similar species.

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The antennules are the 2 short middle things flicking up and down

Secondly, we cracked open some mussels and put the meat in a beaker with a hermit crab.  Over the course of 5 minutes we timed how long the individuals would spend actively eating the mussel.

And last, but not least, we coaxed hermit crabs out of their shells and timed how long it took for them to get back inside it.

The actual cajoling of the hermit crabs out of their shells was difficult at times, and took a certain touch.

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The best method seemed to be holding the tips of their shells and lightly shaking them very close to water. Nothin’ like the satisfaction of finally getting them to leave their shell.

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Anyways, the results were… drum-role please…

Not significantly different between different temperature and salinity levels for any experiment!

Average number of antennules flicks per 30 seconds: 74

Average feeding time: 0.58 seconds

Average time to return to their shell: 5.9 minutes


Although our results didn’t show any major differences in behavior between different stress levels, better understanding the possible effects of future changing salinity levels and temperature due to climate change is always important.

Next time you’re at the beach, keep an eye out for hermit crabs – will you be able to pick out Harry from the crowd?


A Real Estate Market as Brutal as Vancouver’s

Most millenials in Vancouver can relate: the low availability of decent, affordable housing in the city can sometimes make house-hunting feel like a brutal competition. I’ve had personal experience going to view an apartment and waiting in line amongst upwards of twenty other students to interview with a landlord, with the hope of “outcompeting” the others by proving that I am the best prospective tenant.
For invertebrates living in the rocky intertidal zone, competition for a nice place to live can be just as intense. Mobile organisms like shore crabs compete for shelter under cool, shady rocks, where they can avoid predators and direct sunlight (to avoid overheating)¹. Stationary animals like mussels and barnacles compete for space on rock surfaces to attach themselves; like those wealthy UBC students who are able to afford a one-bedroom apartment for over $3000 a month, some of these animals are able to live in more exclusive spots than others like gooseneck barnacles
However, no intertidal critter knows the struggle of finding a place to live like hermit crabs do. Not only do they still need to find spots under rocks, tidepools, and seaweed² like their cousins the shore crabs- they also need to find a gastropod (snail) shell to house their soft, de-calcified abdomen. This diagram shows what I am talking about- hermit crabs have a soft, asymmetrical abdomen (it looks like a tail) so that it can fit inside a snail shell. Which means that without a shell, they are a lot more vulnerable than their fully calcified (hard-shelled) cousins.


       If you’ve ever wondered what a naked hermit crab looks like, this is it! The soft, decalcified abdomen (labelled “smooth tail” has no legs except for small ones used to grasp its shell from the inside. Source: The Hermit Crab Patch.

Seems pretty inconvenient, right? Not necessarily- many hermit crabs, such as Pagurus hirsutiusculus, can leave their shells behind as a defense mechanism when they feel threatened³. This is a great defense tactic if, for instance a fish had the snail shell in its jaws and the crab needs to get away.
In lab last week, we performed experiments on the hairy hermit crab Pagurus hirsutiusculus to determine the presence of interactive effects of temperature and salinity stress on behaviour (read more here!). One behaviour we measured was length of time it takes for a crab to retrieve its shell- a very important survival behaviour.
However when we tried to shake one little crab out of its shell, we noticed something hilarious- another larger, naked crab was trying to forcibly remove the littler one with its claws! I was astonished at how persistent the larger one was, even when we lifted it out of the water. I suppose it just goes to show competitive these animals are willing to be to get a suitable home.


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       A naked Pagarus hirsutiusculus trying to yank another tenant out of its current shell.

However, house-hunting for these rocky intertidal crustaceans is not all ruthlessness… This hilarious BBC snippet shows tropical hermit crabs lined up in order of size to switch shells that they all have outgrown- this level of cooperation is remarkable for backbone-less critters!




Unfortunately, at the end of the switcheroo, one individual is without a shell and has to settle for one that’s a bit too big and has a hole… as a broke university student who’s had to settle for suboptimal basement suites in this real estate market, I can relate.

1. Steinberg, M. K. & Epifanio, C. E. Three’s a crowd: Space competition among three species of intertidal shore crabs in the genus Hemigrapsus. J. Exp. Mar. Bio. Ecol. 404, 57–62 (2011).
2. Meschkat, C., Fretwell, K. & Starzomski, B. Hairy hemit crab Pagurus hirsutiusculus. Biodiversity of the Central Coast (2014). Available at: http://www.centralcoastbiodiversity.org/hairy-hermit-crab-bull-pagurus-hirsutiusculus.html. (Accessed: 12th March 2017)
3. Story, R. M. & Steitz, T. A. © 19 9 2 Nature Publishing Group. Nature 355, 242–244 (1992).

Climate Change and the Hairy Hermit Crab

This week, we had the pleasure of playing with hairy hermit crabs, and testing how decreased salinity and increased temperatures in the ocean will affect them. These two factors are interesting when we consider climate change. Temperatures are on the rise globally, and as a result, glaciers are melting and increasing the amount of snowmelt entering our oceans. This causes problems for marine animals of all kinds, as their bodies are not adapted to warmer and less-salty oceans. With this in mind, we set out to see how warm temperatures, low salinity, and then the combined factors affected our small crustacean friends.

Hermit crabs have little antennules, located between their eyes, which are chemosensory—essentially, they detect tastes and smells. To flick their antennules, they must


A homeless hermit crab finding his shell again! Video credit: Megan Crofts

be able to contract their muscles rapidly, requiring a lot of systems to be working correctly, many of which require specific temperatures and salt concentrations. Next we popped in some fresh mussel meat for the crab to feast on and timed how long the little guy chomped away on its meal. For our final test, we imitated a predator and scared the little hermit crab out of his shell. This specific to this species of hermit crab, as it will leave its shell quite readily (especially if the shell is too small to be a safe refuge anyway). But it won’t want to be homeless for long, and will be searching for a shell soon.

Interestingly, our results were not significant; meaning we can’t confidently say decreased salinity or increased temperature have substantial impact on these three behaviours in hermit crabs. There are multiple possible explanations for this. Maybe our Vancouverite crabs have adapted to changing ocean salinities because they deal with summertime influx of freshwater into the oceans from the Fraser River. Maybe hairy hermit crabs are uniquely able to withstand salinity and temperature stress. BUT this doesn’t mean that hermit crabs would be happy as a clam in a hot tub, or that you can plop a marine hermit crab in your freshwater fish tank at home and he’ll be okay. Actually, it could be far from it. This experiment could simply mean we weren’t looking at the right thing. Sure, these three behaviours seem to not be impacted by climate change stress, but maybe other really important behaviours will be. Maybe the differences weren’t notable at the temperatures and salinities that we were testing. Science is not so simple that we can look at our (frankly, quite weird) results and say they prove that these adorable hermit crabs will definitely be fine as our planet changes. Sometimes, weird results just give us reason to pause, look at what could’ve gone wrong, and try, try again!

Are hermit crabs stressed out by climate change?

The world’s oceans are expected to undergo some changes due to global climate change. Shifts are already happening now, but are expected to become more pronounced in years to come. Currently, in some parts of the world we are already seeing water temperate changes, ocean acidity dropping, and ecological shifts in environments.

Currently, scientists are investigating the effects climate change could potentially have on organisms and habitats of the worlds’ oceans. Initially in climate change studies, scientists manipulated a single variable- for example, temperature. But the reality of global climate change is it will not only affect a single aspect in the world’s oceans- it will likely affect multiple. Climate change is predicted to shift environments’ temperature, salinity, acidity, oxygen levels, and more. It is important to investigate the effects multiple stressors could have on organisms to fully understand the extent to how climate change will affect these organisms and alter ecosystems.

We set up a fully factorial design, a study design that allows us to test multiple stressors on an organism, on the intertidal hairy hermit crab, Pagurus hirsutiusculus. We exposed hermit crabs to high temperature, low salinity, and a treatment where they received both stressors- high temperature and low salinity. Temperature and salinity stress are expected in the worlds’ oceans in future centuries.

In our first experiment, we counted the number of antennule flicks for 30 seconds. Antennules are used to sense chemicals in the water, it lets the hermit crabs know where there might be food or a predator. There was more antennule flicking in the high salinity than lower salinity treatment in both high and low temperatures tested. This might suggest that muscular activity is affected by salinity, that hermit crabs may be better able to move and contract their muscles at higher than lower salinities.

In our second experiment, we recorded the amount of time a hermit crab spent feeding on mussel tissue in 10 minutes. Stressful environmental conditions could affect an organisms’ feeding rate but we found no trends in feeding times in either temperature or salinity treatments.

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A hairy hermit crab, Pagurus hirsutiusculus, eating mussel tissue. Photo: Brittany Ng

In our final experiment, we removed hermit crabs from their shells and recorded the time it took to return to their shell. Seeking a shell is important for hermit crabs because they provide protection from predation and help retain moisture. Temperature and/ or salinity stress could affect the hermit crabs’ ability to detect a shell in its environment or the need to seek shelter may become stronger when the organism is stressed. However, we found no trends in the time it took to find a shell between any of the treatments of temperature or salinity.

Being an intertidal organism, hermit crabs may already possess strong adaptations to large fluctuations in temperature and salinity and are largely unaffected by them because they experience these changing conditions daily. Perhaps intertidal species, like the hermit crab, will be excellent and successful competitors in changing ocean conditions due to global climate change.


They shore like rocks!

If we give Mr. Krabs a choice between a refuge made with rocks and no refuge, what would he choose? What if we shock Mr. Krabs with super salty water and freshwater, will his decision be the same? Let’s find out!


Hemigrapsus oregonensis in its natural habitat (PC: http://bugguide.net/node/view/521931/bgpage)

When you walk along the beach during low tide, have you ever lift up a rock and look what is hiding underneath? The green shore crabs (Hemigrapsus oregonensis) in the intertidal zone does not live inside an anchor like Mr. Krabs, instead, they tend to live under rocks. Underneath the rocks, the crabs have protection from predators like birds, fish, and larger crabs. Since they heavily rely on rocks for shelter, we decided to test if there are any circumstances when Mr. Krabs and his friends forget how to get home.

In Vancouver, the organisms that live in the intertidal zone experience different salinities depending on the different seasons. Unlike Mr. Krabs’ home at Bikini Bottom, the water near the water surface goes through salinity fluctuations due to freshwater that rushes into the ocean. The melted snow from the top of the mountains drains into Fraser River in Vancouver, then the freshwater is dumped into the Pacific Ocean. Therefore, in the summer, intertidal water is not as salty as in the winter. With that in mind, we were curious about how well our crab friends can find their shelters at different salinities.

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In a small aquarium, we built a nice and cozy rocky home for the crabs. One crab at a time (so they are not distracted by their friends), we give each of them two minutes to choose between the empty side and the home side. We did the same thing for three different salinities: 15 ppt, 31 ppt (normal), and 45 ppt.

At the end of the experiment, we found that saltier water did not confuse the crabs’ instinct to go home because we got the same result for saltier water (45 ppt) as for normal water (31 ppt). However, low salinity (15 ppt) seemed to influence the crabs. We found that some of the crabs did not frantically run for their lives and hide under the rocks right away in the low salinity treatment. Instead, they seemed to have forgotten which way was home. There are a few different possible explanation that can help us make sense of such behaviour. Maybe Mr. Krabs’ friends’ activity rate is lower in low salinity because they are using their energy trying to adjust to the new salinity. Follow-up experiments should be done to investigate the causation of such confusion.

The green shore crab is an interesting organism to study! If you like to learn more about their natural habitat and life history, check out this link:


Next time you are at a beach during low tide, make sure you gently flip over some rocks and say hi to colonies of cute shore crabs!