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:



Attention all Vancouverites : Free Housing Available at a Beach Near You!

Do you live in Vancouver and are tired of paying rent?  
Great news! I have just become aware of completely free housing right on the beach! There’s only one catch… you must shrink yourself to be about half an inch tall to be able to fit inside. I haven’t been able to figure this out just yet, but if you do, let me know, and we will head over to the beach to claim our new free homes inside acorn barnacles!

Ok, so acorn barnacles don’t provide free housing for us humans (yet)… but they sure do this for other intertidal organisms!

Acorn barnacles are very abundant species that live in intertidal zones  of beaches (the zone between high tide and low tide) all over the world, including Vancouver. They are good competitors for space, and usually form mats of hundreds of individuals all over rocks in the intertidal zone. These mats greatly change the topography of the rocks, providing great protection and habitat for many species like sea snails and isopods (pictured below). And the best part is, the barnacles don’t ask for anything in return.


Barnacle mats in intertidal zone at Acadia Beach, Vancouver. Look closely! Can you spot any sea snails in between or inside the barnacles? (Pictured by Maria)


I was so taken away at the selflessness of this creature, so for my independent project I decided to learn more about how acorn barnacles provide habitat for other intertidal organisms and if some organisms preferred this type of habitat over others.

In short, I found that intertidal isopods (pictured below) actually love living on top of barnacles. Barnacle habitat seems to provide these little guys with protection from many of the scary stressors of the intertidal zone such as thermal stress, desiccation, wave action and predation. I also monitored two other organisms, sea snails and amphipods, however these two organisms did not show a preference for barnacle habitat. My thoughts are they are searching the housing market for something a little more upscale… perhaps some algae canopy.


A close look at a marine isopod. Photo from: 


Barnacles sure are amazing creatures for doing this for other organisms, however they are not the only ones who do! In fact, many animals in many different ecosystems create, maintain or modify habitats which benefits other species in their ecosystem. Animals who do this are very important to their ecosystems and are called “ecosystem engineers”.

Beavers and corals are two great examples of ecosystem engineers. Corals provide a framework for marine habitats that most coral-reef organisms depend on, and beavers build dams which support extensive wetland habitat and tons of species!

If you’d like to learn more about amazing ecosystem engineers, check out this video explaining why termites play such key roles as ecosystem engineers in the African savanna:

And to learn more about the amazing acorn barnacle, read this:

These Snails Did Not Want to Play Hide and Seek

If you were a 2.5 cm tall snail, would you be afraid if alerted to the presence of a 20 cm long, unfamiliar predator? Well, if I were the snail, I think I would! The project that I conducted over the past few weeks points to the contrary; the Littorina littorea sea snails, also known as the Common Periwinkle, that I exposed to the presence of a large and potentially predatory Dungeness crab did not seem to show a tendency to look for places to hide, a curious result.

Sea snails often show a common response to predators – they move upwards and outwards away from the potential danger! For my project I looked at a different response; do they move towards rocks to find refuge from the chemical presence of the Dungeness crab?


One of the Common Periwinkle used in my project. (Photo Credit: Casey Chiu)

In order to assess if the sea snails were looking for hiding places in the presence of chemicals from the Dungeness crab, I looked at how much they ate in the hiding places provided in my experiment; the more algae, one of their favourite food, they ate in the hiding places, or rocks, the more time I assumed they spent hiding. The feeding action of the Common Periwinkle when eating algae is a very interesting one. They have a tongue-like structure called the radula in their mouths. The radula has tooth-like projections that allow them to grind off algae for consumption.


Ulva lactuca on the rocks – a favourite species of algae of the Common Periwinkle. (Photo Credit: Mitchell Sattler)


The radula of the Common Periwinkle. (Image from

After leaving the snails in water with Dungeness crab chemicals for four days, I recorded my data and then looked at my results. Like I mentioned before, I didn’t find that they spent more time hiding in the presence of the predatory Dungeness crab chemicals. Why would that be? It seems logical that they would try and hide from a potential predator. Well, there are number of things that could be responsible for this result. Maybe the escape response of the snails to this crab is primarily the action of crawling out of the water, not looking for rocks to hide under. Another response could be the snails hiding in their own shells! Common Periwinkles have a special structure called the operculum. The operculum acts like a swinging gate that can close shut when they need it to escape danger. Lastly, it may also have to do with the predator. Dungeness crabs live in the Pacific, while Common Periwinkles are from the Atlantic. It could just be that they don’t recognize the scent of the Dungeness crab as an alert that a predator may be nearby! Regardless, the interactions and responses between species in our oceans are complex and they are definitely always interesting!

To learn about the interesting account of the Common Periwinkle in North America take a look at this link:

“Plans are an invitation to disappointment.”

Ah yes, the end of term. A time where students invariably have loads of assignments due and exams to study for. I had the added complication of having to fly to eastern Canada three times. Fortunately, I had interesting projects to work on.

My classmates and I all came up with grandiose plans, but as in battle, no plan survives the laboratory. This brings me to my first point: Experimental design is very important. Scientists come up with questions then design experiments that control as many variables as possible in order to answer the questions. If the design is poor, it could mean hundreds of hours lost. If the design is good, it will survive with minor alterations.


“Things that can go wrong…”: You can try and prevent unwanted “alterations” to your experiment by leaving a nice sign.

Personally, I wanted to test how strongly mussels attach to docks and other construction on the ocean. A bit about mussels, they attach themselves to hard surfaces using tough fibers called byssal threads that have a sticky end; the attachment plaque. Each mussel lays dozens of threads, extending their foot out of their shell and secreting protein from the byssal gland found inside of their shell. This process takes only around 3 minutes per thread! Mussels are actually mobile; they can detach, move, and reattach. I wanted to test how well the plaques stuck to different construction materials, aka substrates. My plan was to use a dulled razorblade, to target the plaque portion of the thread, attached to a spring scale in order to measure the relative force necessary to detach the mussels. I set up 120 mussels on the substrates and then flew out east. When I returned four days later, I began testing and immediately found out that the spring scale was not sensitive enough to record the detachment force.


“will go wrong…”: In our lab, we learned that crabs will get everywhere. Even into isolated experiments. 

This brings me to my second point: Science is limited by resources and equipment. In every lab across Canada, researchers constantly apply for grants to the point where some feel like they do more proposal writing than research. Without enough money for labour or equipment, impeccable experimental design will not matter. I was short on both time and equipment. I shifted my design and instead counted the number of threads mussels lay on the different substrates, hypothesizing that they would lay more on surfaces they had a hard time attaching to. It turned out that, on average, they lay the same number of threads no matter what surface they are on.


“or at least most of the time!”: Something went according to plan! Here you can see the byssal threads attached via plaques to the aluminum substrate.

Some interesting observations I made were that mussels would much rather stick to each other than anything else. Dozens of mussels will clump together with only a couple of them holding the group to the substrate. I also saw a couple of isolated mussels that did not attach to the substrate at all, but instead had a dozen threads that attached to themselves. Those must have been some confused mussels.

If you are interested in reading the detailed article about my research, you can read it at the following link:

For more about the specific mussel I studied, Mytilus trossulus, a native species of the British Columbia coast, check out the following links:

Monkey Sea, Monkey Do

Sea monkeys, or brine shrimp, are invertebrates that can tolerate intense conditions like no other. They may seem like simple novelty pets, but their calm demeanor hides their extreme side. Brine shrimp are particularly good at living in water with high salt concentrations, surviving in water where the salinity can be as high as 300 parts per thousand (for a reference, the ocean is generally around 30 ppt!). They can produce cysts that lay dormant for years until conditions are favorable for hatching, making them ideal survivalists, and pets. I became interested in these robust little shrimp and decided to study how they respond to quick changes in salt concentrations.


Brine shrimp life cycle.

Salt is a major limiting factor for aquatic species, which makes the durability of brine shrimp so intriguing. One explanation for their high tolerance is that it helps them avoid predators: nothing can eat you if your enemies die when they step foot in your home. But this evasion may come with a cost, as the brine shrimp need to expend more energy to maintain their health when exposed to high concentrations of salt. Salt also seems to affect young shrimp more than adults. Scientists have studied the effects of long-term exposure to high salinity but know less about how brine shrimp respond to fast salinity changes.

I wanted to see if quickly changing salinity altered brine shrimp behavior. I collected some brine shrimp from a toy store and hatched them in my room, raising them in 30 ppt water. They breathe through their feet, so I measured how fast they beat them in response to changing salt concentrations. I found that younger shrimp (one-week old) increased their beating activity when exposed to higher salinities, but that juveniles (two-week old) had no response. This shows how there may be costs associated with extreme lifestyles, as young shrimp need to expend more energy to tolerate high salt concentrations.

This highlights the powerful rule in nature that there are no free lunches. Brine shrimp are just one example of the tradeoffs often found in biology. While being able to live at high salinities is beneficial for predator avoidance it is not so simple as just hopping pools; salt tolerance requires energy and appears to put stress on young brine shrimp (many studies have found that baby brine shrimp aren’t as good at tolerating salt as adults).


Mono Lake in California, a saltwater lake where brine shrimp live

Brine shrimp are by no means the only extremophiles out there. There are species that live in such intense environments they are used as models for organisms we may find on other plants! Some organisms can only live in areas without oxygen, while some can live at pressures over 1000x that on the surface of the Earth. Studying these extreme creatures is a useful way to understand just how flexible, and resilient, life can be.


Check out this site if you are interested in learning more about brine shrimp:

Cover picture from

Gary doesn’t like copper

We all know Gary the meowing snail from Spongebob. A list of things that he likes probably include: Spongebob, crawling, and eating. What about a list of things that Gary doesn’t like? I bet you didn’t know that Gary doesn’t like copper.


Gary the snail. Photo: Spongebob Wikia.

As it turns out, no snails like copper. And it’s not just snails, it’s probably all the sea critters that live in Bikini Bottom too- sponges, sea stars, octopuses, crabs. Copper is a common marine pollutant that harms many animals. The most common source of copper pollution in the water is from antifouling paints that are applied to boats to stop animals from growing and settling on the boat. Copper is especially good at preventing the growth of animals so it’s used in antifouling paints as a biocide.

Knowing that copper is harmful to many marine organisms, I did an experiment to see what copper does to snails. I wanted to find out what copper concentration was deadly for snails and how copper could affect their feeding and response to a predator. I predicted the rate of snail deaths would be greater at higher concentrations of copper and that feeding and a response to a predator would be reduced. I placed common periwinkles in different containers of seawater that contained various concentrations of copper. After being exposed in copper water for 3 days, I counted the number of dead snails and with the ones that survived, I tested their feeding and predator response behaviours. I gave the snails sea lettuce to see if they would eat it. To test the snails’ predator response, I would touch a sea star’s arm to the snail and record their crawling speed. In short: I found that copper does not do any good for snails. The more copper there was in the water, the more snail died, the less they fed, and they did not crawl away when there was a sea star predator. This has big implications for the toxic effects copper has on snails. Being exposed to copper pollution can prevent snails from eating, growing, reproducing, and escaping predators. Ultimately, at high enough concentrations, it kills them.


Seeing if the common periwinkle, Littorina littorea, will feed on sea lettuce. Photo: Brittany Ng.

These results shed some light on the negative impacts copper has on snails, and probably other marine animals as well. Areas where there are a lot of boats, in harbours and marinas, there is bound to be marine pollution. Animals that live around these areas may be harmed as pollutants such as copper are present in the environment. If copper can kill snails, decrease their feeding, and make them unable to escape predators, continued pollution may cause these animals to disappear. And the toxic effects of copper extend beyond snails, they effect other organisms in the habitat that they’re present in as well. We could see changes in marine ecosystems as the abundances of animals decrease from the continual exposure to marine pollution.

Does Size Really Matter?

How many different species do you think are within 1 square foot of you right now?  How about 10 square feet? Or a square mile?

Now how do you think that would change if you were standing in the middle of nowhere with nothing close by?

The answers to these questions have often been explained by 2 well known theories in biology:

  1. The species-area curve, where the number of species increases with area size
  1. The insular biogeography theory (aka the island biogeography theory), where the idea is that less species arrive at more isolated areas


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Basic idea behind the island biogeography theory (less arrows, or ‘species’, reach the farther island).  Picture from

Sometimes these theories aren’t completely true in all ecosystems though so I was interested to see if they were for Acadia Beach, Vancouver.

Since beaches are constantly being disturbed by changing tides and large weather events, the animals that live there have to be able to return to rocks quickly.  Does the size and remoteness of a rock change the number and speed of animals returning to rocks after a disturbance?

This led to 2 questions I decided to investigate:

  • Will there be consistently more invertebrate species on bigger rocks?
  • Will rocks that are farther away from other rocks (more isolated) have less invertebrates return to them after being cleared?

To answer these questions, I counted the species richness (# of species) on the bottoms of rocks of varying sizes (measured by surface area).  I then cleared the rocks (scraped off all the animals on the bottom) and moved 20 to an empty, “isolated” zone on the beach, while leaving 20 rocks in the same spot I found them.

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Rocks before and after being cleared

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“isolated zone” circled in red

1 day later, and again 1 week later, I came back and counted species richness on the moved and unmoved rocks.

The most common things I came across were barnacles and mussels (on the first day only, since they take a while to come back), crabs, isopods and amphipods.

Here are the take-aways I got after analyzing my data

  • The size of a rock (ie the surface area) did affect the species richness. More species were found on larger rocks (about 1 extra species for every 250cm2 of rock).
  • A week after rocks were cleared, species richness increased on non-moved rocks but returned to the same value on moved/isolated rocks… Maybe the isolation made it so there were less species that went back to the moved rocks than the non-moved rocks, but I can’t be sure from these results.


Overall I found that size does matter (sorry guys), but the effects of isolation weren’t as clear.  These are just the results for 1 specific ecosystem, how do you think the effects of area size and isolation would change in an ecosystem near your home?  If you’re curious, try doing a little science experiment like mine and discover something new about the place you live!