My weekend with some seriously stressed out sea stars

The past year I have immersed myself into the world of intertidal ecology and have found myself obsessing over sea stars. Most people actually share my fondness of these charming animals, but maybe not to my extent…. so I naturally found myself doing my final project on them.

One of the patterns I have observed around Vancouver, is it’s pretty challenging to find sea stars on the rocky shore during the summer. Sea stars are actually the most abundant during winter. I expect few people to know this because they likely spend their winter nights inside their warm houses, but not me! I bundle up and spend my winter nights counting these critters, and let me tell you, there are tons of them! There are two main sea star species you are likely to find around Vancouver, the mottled sea stat, Evasterias troschelii, and the ochre star, Pisaster ochraceus, . I have additionally observed that Evasterias seems to completely disappear from the intertidal where as Pisaster can still be found occasionally. So why do sea stars retreat from the intertidal in the summer and why does Evasterias do it more than Pisaster? Obviously, an experiment was needed to settle this.

Maybe sea stars are not able to handle the extreme conditions experienced in the intertidal during the summer, and they retreat to the subtidal to escape. Vancouver is by the Fraser River and each summer the river’s output increases and makes the sea water less salty (lowers the salinity). Temperature also increases as the sun cooks the intertidal. Sea stars do poorly in low salinity, check out this study, so maybe this summer condition was driving the sea star retreat. Temperature may also be a player here, so I decided to test this too. Specifically, I wanted to see how lowering salinity and increasing temperature, affected the activity of sea stars, and whether any negative effects were more harmful to Evasterias.

To test this, I placed sea stars of both species into tanks of low salinity and high salinity, across a range of temperatures from 12 degrees Celsius to 18 degrees Celsius. To see how activity changed for each species, I flipped sea stars and timed how long it took for them to right themselves. This felt a bit cruel at times, especially for the ones that never made it back rightways up.


An Evasterias trying to right itself under in a low salinity tank. Photo credit: Sharon Kay

I found that low salinity, but not raised temperature, decreased the activity of both species, and that Pisaster was just as affected as Evasterias. So it looks like salinity could be driving the retreat of sea stars during the summer, but maybe other factors are causing Evasterias to disappear entirely. Maybe biological factors may be driving the disproportional retreat between my two species. My next future experiment…. effect of gull predation!


A sea gull snacks on a sea star. Photo credit:



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:

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:

and give this article a read for further information:

Forget the view from above, look under your boat for the best marine wildlife!

If you are like me, you’ll take any chance you can get to head out on the water, with the faintest hope of spotting some rare marine wildlife. Almost anyone (minus those prone to sea sickness) have the desire to get up close and personal with the wildlife of the ocean, however most people don’t, seeing as the majority of people living near a coast don’t own a boat or have access to one. Turns out, as I learned this week at the Coal Harbour Marina in Vancovuer B.C., turning on the boat isn’t all that necessary. As long as you can find your way to the nearest public dock, a seemingly unseen world of marine animals awaits you.

Now I’m not promising you are going to see a pod of dolphins pop up between a moored boat. If fact it’s doubtful you will see any of the kinds of animals you are used to seeing at all. Here in urban marinas, exists a bizarre community of organisms most people have never heard of. This is because even the people who own their own boat or regularly walk along the dock side, tend to miss these animals from the typical person’s bird’s eye view. I suggest getting a bit lower, and leaning over the edge of a dock or boat (while making sure someone is holding on to your legs!). Just underneath these submerged structures is a neighbourhood of slimes, sponges, mussels, and even animals disguised as algae.

The wondrous world of marine invertebrates growing out of our sight. Photo by Harsonic boats.

At first these critters might not look as striking as the friendly face of a harbour seal, but I think that is just from the public not being exposed to the everyday sights of these underappreciated species. Try pulling up a submerged rope or taking a scraping from underneath a boat, and you will see what I mean. Turns out the slimes are actually called Tunicates, an evolutionary group that functions as a link between invertebrates and vertebrates (us!). Here in Vancouver B.C., the Tunicates found on most docks or boats belong to the species Botryllus schlosseri. The animal you see below shows the intricate pattern created by each individual Tunicate grouping together in an organized colony.

The Golden Star Tunicate growing on mussels shells underneath a dock. Photo by J. Martin, Department of Fisheries Canada.

Golden Star Tunicate up close. Individual Tunicates bundle together to create a colony of star-shaped patterns. Photo by David Fenwick, Aphoto.

This species has an interesting story as it is an invasive species, originally from the Mediterranean Sea. It was introduced to the Pacific ocean through shipping traffic and may be negatively impacting the rest of the native community of animals living under the docks. Without scientist first poking their heads under boats due to curious nature, this species may have not been detected in the first place. So now that you are running towards your nearest marina, make sure you grab a bucket and try not to be too modest as you collect some Tunicates for your next art project. Good luck with the smell…

For more info on invasive Tunicates go to: