Warning: salt is bad for you!


Green shore crabs from BC coast (PC: Casey C.)

Once upon a time, a bunch of green shore crabs (Hemigrapsus oregonensis) decided to have a race among themselves. Instead of having a simple race where they time how long it takes them to run one meter, they decided to test salinity tolerance.

One of the crabs being adventurous suggested, “hey guys! Let’s see if salt can be our magic potion to make us run faster!”

Another crab said, “That’ll be cool! I remember my parents once told me that we’re osmotic regulator!”

A little baby crab asked, “What does that mean?”

“It means that we can regulate how much salt is in our body independent to the environment!”

osmotic regulator

osmotic regulator vs. osmotic conformer (https://www.studyblue.com/notes/note/n/exam-3/deck/8949610)

The adventurous crab then said, “well if we are not affected by just a little change on salt, then let’s try the extreme concentration of salt!”

With that said, some crabs withdraw from the race because they didn’t think it was a good idea, but some stayed in the race. The rules of the race were that each participant had to spend every second of every day for a in either super salty water or water with low-salinity water. The crabs that wanted to join the race but were hesitant chose to live in the water that they’ve always lived in. three hours later, the fraction of the participants gathered and started their first race. One at a time, the crabs took turn to run one meter; a referee/ score keeper tracked the time that each crab took to finish one meter to calculate their speed. Three days after the first race, a different fraction of the crabs had the same race. Then a week later, the last fraction of the crabs had the same race again.

At the end of the last race, the referee called a meeting and announced the results. “Before I announce the winners, I’d like to take a moment and remember the fellows that passed away because they couldn’t cope with super high amount of salt. It was a tragedy, but they taught us that we suck at regulating when we are hypo-osmotic to the environment. Now, let me announce the results!”

While referee was talking, most of the folks that exposed themselves to a lot of salt were still lethargic and didn’t know what was happening.

“So overall, it turned out that y’all who diluted your water (low salt content) ran faster than everyone! The folks that played it safe and stayed in normal water were second place, and the brave and adventurous bunch who chose lots of salt ran the slowest!”

A grandpa crab just happened to pass by and heard the result, he said, “my generation had the same race when we were young! We had the same result too. Want to know why?”

“I want to know! I want to know!” a crab that lost the race yelled.

“It’s because we are used to the low salt content that happens in the summer, so we are well adapted to low salinity and are fantastic hyper-osmotic regulator. However, we don’t normally experience super salty water, so our body is out of whack and we spend lots of energy trying to restore homeostasis!”

“Wait…why is there less salt in the water in the summer?” a curious crab asked.

“Because snow melts on the top of the mountain, and all the water drains into the ocean and dilute the water,” answered the grandpa. “As a lesson, don’t forget to tell the next generation what you learned from this race so they don’t sacrifice themselves for science again!”

More about osmoregulation of H. oregonensis: https://www.jstor.org/stable/1539589?seq=1#page_scan_tab_contents


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!


Taking Without Permission (a.k.a. Stealing)

A huge sign at the Royal Vancouver Yacht Club entrance says “members only”. How can we get in without paying for membership? Be part of the BIOL 326 class! Earlier this week, our class was on a mission to find some native and invasive invertebrates. What better way to spend a beautiful afternoon hanging over the edge of the deck looking for invertebrates (without falling into the water!). Before we dive in and talk about our interesting observations, let’s understand what invasive species are and where to find them.

Just like the French colonists who colonized North America in 1534, invasive species are introduced to a new habitat and drive the native species to vulnerability. They can compete for food and/or space with the native species. One of the invasive species that we investigated during the lab was the golden-star tunicates. They are named for their star-shaped colonies. The other species we collected was the Japanese skeleton shrimp that holds onto sea plumes. We looked for them at fouling communities, which are communities on artificial surfaces like docks, rocks, boats, and marinas. The reason why we chose fouling communities to study invasive species was because fouling communities are especially vulnerable to invasive species.

During the lab, we were split into two groups to go to two locations of Royal Vancouver Yacht Club that have different salinities. My group went to the one at Jericho Beach, and we did not find any invasive tunicates (which is a good thing!) but the other group did at Coal Harbour. (Hmmm…I wonder if their survival depends on the ocean salinity…) They also collected some colonies back to the lab so we could look at the them closely under the microscope. The subtle movement of the tunicates were quite interesting. When we looked carefully, we could see the water movement in through the siphons and through the bodies!

(more about golden-star tunicates from Fisheries and Ocean Canada: http://www.qc.dfo-mpo.gc.ca/publications/envahissant-invasive/botrylle-etoile-golden-star-tunicate-eng.html)


Golden-star tunicates! Aren’t they gorgeous! (www.exoticsguide.org/botryllus_schlosseri)

While the other group found the golden-star tunicates, my group found the Japanese skeleton shrimps! They were hard to find because they are so tiny (~3mm) not very abundant. It was easier to look at them under a microscope in the lab. The one that my partner and I observed under the scope was pregnant! When we zoomed in even closer, we could see her tiny heart beating (212 beats per minute!). After a few minutes of observing our skeleton shrimp, she stopped moving, and her heart stopped! We thought it might be the lamp of the scope that was warming up the water. After we changed the water, she returned to life! It seemed like Japanese skeleton shrimp survival depends on the water temperature…


The swelling is her belly filled with eggs! (PC: Casey C.)


Watch me stretch! (PC: Casey C.)


Fresh out of the water! Can you see me? (PC: Casey C.)

Next week’s lab we are looking into what really determines the survival of these invasive species, so stay tuned…