How to Stay Cool in the Intertidal

We are lucky to have the privilege of using the weather forecast to prepare for the weather. We can dress warmly when we expect cold temperatures, or wear a hat and carry around a water bottle to stay hydrated during extreme heat.

intertidal zone

Intertidal zone during low tide (PC:


The intertidal zone is an area in marine environments that are alternately covered by the sea in high tide and exposed to air during low tide. Other hazards include exposure to dangerously high temperatures and desiccation. Organisms that inhabit this environment must have adaptions for extreme conditions in both wet and dry conditions. Sea stars keep themselves cool after heat exposure by soaking up water to protect themselves from the blazing temperatures that persist when the tide goes out. Hermit crabs use their shells to shelter themselves from high temperature and retain water in their shells. How do intertidal snails, Littorina Littorea, adapt to heat and desiccation stress?


L. littorea in its shell in hot & dry environment (PC:Juhae Oh)


Snails have shells and are able to store water in their mantle cavity.  Would they store more water and take longer to come out of their shells after suffering desiccation and heat stress? In my experiment, different temperature treatments representing hot, warm, regular, and cold environmental conditions were set up. Each temperature treatment was paired with wet and dry environments representing respective high and low tide conditions. The effects of temperature, water level, and the combined effect of both were examined by quantifying amount of water stored in the snail’s mantle cavity, and the time it takes to come out of its shell. Water stored in the mantle cavity was calculated by change in weight. The initial weight of individual snails was measured before exposure to treatment conditions. After treatment exposure, they were placed in regular seawater to give them time to store water, then reweighed. Any change in weight was assumed to be from water stored in mantle cavities. The time it takes the snails to come out of their shells was also observed to see if shells were utilized as a form of protection. Results revealed a significant difference in the time it takes for them to come out of shells. Snails in hot temperatures did not come out of their shells regardless of wet and dry conditions. Snails in regular and warm temperatures took significantly longer to come out of their shells in dry conditions than wet conditions whereas in cold temperatures, they took longer to come out in submerged conditions. There was no significance in change in weight there. My experiment suggested that snails prefer to use their shells to protect themselves instead of storing water in their bodies, just like some people choose to stay away from the sun rather than carrying around water while exposing themselves to the stinging sun rays.


Click here to learn more about how plants and animals survive in the intertidal.

Caprellid fight club: spines vs poison tooth

The first rule of fight club is that you don’t talk about fight club. I set up a competition for space between two species of caprellids, and I’m going to break the first rule and tell you all of the epic details. Caprella mutica is an invasive species whose back is covered in spines, and Caprella laeviuscula is a native species that has a poison tooth it uses to kill enemies. This sounds like a pretty epic fight, and I’m sure you’re all dying to see some action photos.


Can you see them fighting? I think one just used a right hook! Photo: Emily Lim

These organisms are only about 15 mm long, and I need to use a microscope to identify them, but that doesn’t make their battles for space any less cool.


C. mutica. Photo:


C. laeviuscula. Photo: http://www.dfo/








If you go out to a dock in Vancouver and lean over the side, you’re most likely to find the native C. laeviuscula and the invasive C. mutica clinging to the Obelia growing on the dock. I started getting really interested in caprellids, so I thought it would be a fun project to investigate competition for space between these two species!


I also decided that Obelia makes a great beard. Scientists are weird, ok? Don’t judge me. Photo: Chris Harley

Now I know what you’re thinking. Why does anyone care? Beyond my own personal interest, I think caprellids will make really good model organisms. Model organisms are organisms that we might not care about much, but they’re useful for testing theories on. One of the most famous model organisms is the fruit fly. No one really cares about fruit flies, but scientists have used them to test many hypotheses, especially in genetics. I think that caprellids would be a fun species to use to answer questions about ecology, but in order to do that I need to know more about how these two local species interact with each other first.

In order to see which species is a better competitor for space, I set up 9 plastic cups, each with a little piece of Obelia covered in caprellids. After letting them fight for three hours, I counted how many C. laeviuscula were booted off the Obelia when it was just C. laeviuscula, compared to when I also had C. mutica in the cup. I found that when the invasive C. mutica was present, a lot more C. laeviuscula were kicked off the Obelia. This tells us that when we give the two species a limited amount of space, C. mutica is better at fighting for that space than C. laeviuscula. Despite C. mutica’s spines and C. laeviuscula’s poison tooth, none of the caprellids were killed, just displaced.


Except this guy, who was beheaded in a pilot experiment. Photo: Emily Lim

If you want to learn more about these weird, alien looking crawly things, check out this blog here!

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 (

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:

The Great Mussel Feast starring Hungry Hungry Hemigrapsus

Rising ocean temperatures and decreasing salinity are predicted to affect (and are affecting) the world’s oceans… but what does this mean for our favourite intertidal invertebrates such as shore crabs?

For my independent project, I chose to study the shore crab Hemigrapsus oregonensis and the effects of temperature and salinity on their feeding behaviour. H. oregonensis inhabit muddy banks in rocky intertidal zones from Alaska to California (Sliger 1982). I wanted to measure how many minutes out of a five minute period they spend feeding on their favourite prey, crushed mussels.

I predicted that in the high temperature conditions the crabs would spend more time feeding because the rate of metabolic activity is higher at high temperatures and the crabs face greater metabolic demands. At low salinity conditions, crabs consume more oxygen suggesting higher metabolic activity. This led me to predict that the crabs would also spend more time feeding at low salinity. When the two conditions, high temperature and low salinity, were paired together I expected the crabs to spend the most amount of time feeding when compared to the high temperature or low salinity conditions alone.

To test my predictions, I set up four tanks with different combinations of temperature and salinity as shown below:

Screen Shot 2017-04-12 at 11.13.09 PM

In the center of each tank I placed some crushed mussels. Then I placed one crab in the tank at a time and recorded how much time they spent munching away on the mussels. The crabs had been in the lab for 2 weeks and were starving at this point, so they were quick to attack the mussels and start eating!

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H. oregonensis devouring mussel tissue. Photo credit: Arpun Johal

I found that salinity and the temperature-salinity interaction did not have significant effects on the amount of time that the crabs spent feeding. However, temperature did have an effect. The crabs spent less time feeding in the warm temperature compared to the high temperature. This was surprising because I had predicted the opposite effect!

After looking at some previous studies on temperature and Hemigrapsus, I decided that my results may have something to do with the crabs’ thermal tolerance. The warm temperature (22°C) was higher than what the crabs are normally used to and this temperature may have been too extreme for the normal function of the crabs. Hence the observed decrease in feeding under high temperatures instead of the expected increase. Increases in temperature only increase the rate of metabolic reactions to a certain extent. The graph below demonstrates this:

The following video also explains the connection between optimal temperature and metabolic activity.

Although my experiment did not find high temperature and low salinity to have a significant effect on the feeding behaviour of Hemigrapsus, the effects of increasing temperature and decreasing salinity on marine intertidal species and communities still remains an important question.

The following video explains the effects of climate change on the world’s oceans.


Sliger, M. C. (1982). Distribution and microhabitat selection of Hemigrapsus oregonensis (Dana) and Pachygrapsus crassipes Randall in Elkhorn Slough, Monterey County, California (Doctoral dissertation, California State University).

Majestic undersea meadows and their hungry residents

Like most biology enthusiasts, I love an excuse to go into the field. So when given complete freedom to investigate any invertebrate question we wanted for our final project, I didn’t have to think twice before choosing to study invertebrates in seagrass meadows: a severely underappreciated ecosystem type.

Yes I know- seagrass sounds like just about the most uncharismatic thing there is. Grass isn’t very interesting at all…

boring grass

Figure 1. Boring land grass. Image: 1234RF Stock Images

… so grass under the sea probably isn’t that much more interesting, right? Perhaps these images might change your mind…

Some words that come to my mind from looking at these ones include “tranquil”, “majestic” and “lush”, which is a far cry from the average person’s conceptions of grass. So what’s the big deal with seagrass, and more importantly, what on Earth do invertebrates have to do with them?

Unlike seaweeds, seagrasses are marine angiosperms: land plants that have colonized the ocean. Different species of seagrasses are found all over the world with the exception of the high poles. As is apparent from the photos above, seagrass meadows are highly productive; the grasses harness energy from the sun, creating far more biomass per unit area than microscopic phytoplankton do in pelagic (open) waters. They also stabilize the sediment, and provide habitat for a diversity of life on the same order of magnitude as some coral reefs, from tiny invertebrates to juveniles of commercially important fish. Invertebrate herbivores (also known as grazers) living in seagrass meadows have one very important job- to eat! Grazers play the critical role of transferring all the nutritious food generated in seagrass meadows to animals higher up in the food web like fish. Juvenile fish that use seagrass meadows as nursery habitat eat lots and gain weight, and eventually they transport this biomass to pelagic waters when they are large enough to leave. In other words, seagrass meadows are important for creating biomass that ends up in open ocean, and grazers are a key player in this process.


Snorkelling at the field site in Tsawwassen to collect seagrass-associated invertebrates for my experiment

Lucky for me, there is a seagrass meadow not too far away where I was able to get my field fix and collect my experimental organisms. The low tides that week were quite high so I ended up having to snorkel to catch them- no complaints there (aside from not being able to feel my face in the 6°C water). I also happened to visit in the middle of an algae bloom; the seagrass was looking pretty scummy from algae growing on the blades.

The most abundant grazers at the field site were the green eelgrass isopod Idotea resecata and the eelgrass limpet Lottia parallella. The results of my experiment showed that both actually prefer eating seagrass over algae, which may make seagrass at the site more vulnerable to decline from being strangled by the algae (More details here). Seagrass meadows are experiencing disastrous losses all around the world; since the 1940s, we have lost seagrass meadows on an order of magnitude of 10 000 km2 1. Despite this, they are not getting nearly as much attention from the media and general public as their charismatic counterparts, coral reefs. Along with conducting research to further understand factors causing their decline, creating public awareness and appreciation of their importance is crucial.


Who needs a tropical reef fish aquarium when you can have a seagrass mesocosm instead?


  1. Orth, R. et al. A Global Crisis for Seagrass Ecosystems. Bioscience 56, 987–996 (2006).

The Intestines of the Earth

Despite most of us paying little more attention to them than a quick pirouette to avoid smooshing them as they crawl on the sidewalk after a spring rain, earthworms happen to be one of the most important soil dwelling invertebrates. In fact, they’re so important that the last scientific book that Charles Darwin ever wrote was about earthworms. So, I invite you on a journey into the soil’s depths, as we get a brief glimpse into the life of Squirmin’ Herman the red wiggler worm (


Red wiggler worm. Look at its shiny, mucus-coated skin! Image from:

Red wigglers are a non-burrowing species of worm. They live in the top layer of soil where their primary food source, organic matter, is abundant. A red wiggler can eat around 2 times its weight in organic matter every day! On top of this, they have huge water requirements. Water is constantly secreted through their skin as a slimy mucus. This keeps their body surface moist, so that they can crawl smoothly through the soil. Their moist skin also helps them absorb oxygen and get rid of carbon dioxide, as like other earthworms, red wiggler worms breathe through their skin!

Given these high organic matter and high moisture requirements, I conducted an experiment to test how they would prioritize these two factors. That is, when given a choice between dry soil that is rich in organic matter but lacks moisture, and wet sand that is rich in moisture but lacks organic matter, which would they choose? I was quite surprised to find that a huge majority of the red wigglers I tested, around 90%, chose the dry soil.

I wondered if there was a reason they might have avoided the wet sand. Perhaps it was because, like us, red wiggler worms can sense and respond to unpleasant stimuli, and might have avoided crawling through the sand as it may have been quite scratchy and painful compared to the fluffy soil. Or, since red wigglers aren’t physically adapted to burrow, they may have been unable to crawl into the dense, wet sand, even if they might have preferred to.

I also wondered how they might cope with the dryness of the soil. I learned that almost all earthworm species can tolerate low moisture conditions through a period of inactivity known as aestivation. Some species dig deep into the soil, and tie themselves into a knot in a mucus-lined chamber to minimize water loss. Others keep their body extended, but stop all activity until conditions are more favourable. As for Squirmin’ Herman, in this experiment it seems he and his friends chose the latter option (pictured below on the right).

ARKive image ARK022318 - Earthworm

Earthworm in knot in “aestivation chamber” during drought conditions. Image from:


Red wiggler worms extended in dry soil in a choice experiment with dry soil and wet sand. Image taken by Brent Ludwig











With that, this brief earthworm journey comes to an abrupt close. However, there are many more earthworm adventures waiting for you outside. Next time it rains, perhaps instead of dodging them, lean in to take a closer look. These underappreciated sidewalk noodles will be pleased to find a friend.

SNAILS: Flipping out, cooling off, heating up, and looking for answers.

Scientists are always trying to answers the big questions; but sometimes to get those big answers we need to start small. Like under-some-dirt-in-your-garden-never-even-noticed-them small.

So I dug out some of our under-appreciated and under-studied critters to start asking the big questions. My research took a closer look at two invasive snail species found in Southwestern British Columbia: the Glass Snail (Oxychilus sp.) and the Grove Snail (Cepaea nemoralis).

To better understand where these snails are likely to live and how they might cope with a changing environment I observed their response to temperature change.

The snails were split into two groups. One set was kept at a chilly 3ºC for 48 hours, the others were kept cozy at 19ºC. When the treatment was over it was time to flip some snails…

Snails are highly motivated to not be stuck on their backs. So one by one I performed a “righting time” test: snails were flipped upside down onto their shells. From that point I timed just how long it took this snail to flip completely back over. This “righting time” is a good approximation of how agile and active that snail is!

Watch below to see righting time analysis for one little Grove snail:


So I flipped and flipped and flipped… and finally the times were all in!

After comparing all righting times I found that both snail species slowed down in response to being left out in the cold!

Interestingly I also found a difference between my two groups: the Grove Snails were a whole lot faster than the Glass snails!

So who was the fastest?  Your friendly neighbourhood Grove snail (Cepaea nemoralis) when kept at a nice 19ºC.

Snails hibernate in cold weather, their body functions slow down as they settle down for their winter snooze. So it makes sense that the cold treatment made both snail species a little less active than their usual speedy-selves.

Explaining the difference in flipping time between species is more complicated… maybe the flat shell of the glass snail is harder to flip with its little body, or maybe grove snails are a little tougher when it comes to spending 48 hours in the fridge!

The primary goal of this research was to provide some understanding of how these species respond to different temperatures, as a baseline for further studies into how they might spread in an environment as invasive species, or as a result of climate change…But it became much more than that! It became an observation of how little we know about these diverse critters.

glass snail pic

Note the translucent shell on Oxychilus sp. (hence the name Glass snail). If you look closely you can watch their lungs pump!

The physical and behavioural differences between just these two species was astounding! They are fascinating, friendly, and wildly understudied. You can identify the snails you see in your garden here, and start making observations! Go forth and discover the drama and intrigue of the daily life of a good ol’ garden dwelling gastropod. 🐌