Biol326: Experimental Biology Of Invertebrates

You’re walking along the sidewalk and suddenly, someone accidentally  bumps into your arm pretty hard. As a Canadian you instinctively say ‘sorry’, but you toss back a dirty look and continue on your way, not noticing that your arm is also back there on the ground.

Image 1: Arm regeneration of sea star; one arm dividing in two. (Photo credit: http://coolmarinescience.blogspot.ca/2012/01/heart-of-silk-sea-star-self.html)

Now this would probably result in a significant amount of blood loss and most likely death for a human. But sea stars have the ability to lose their arms (autotomize) without any serious implications on the animal. Sea stars can regrow arms lost after a disturbance, this is most likely an adaptation to predation, where losing one arm to a predator is better then being totally eaten and dying.

Feather Stars

An interesting kind of sea star is the Feather star, which raises its arms into the water and feeds on particles that get caught. They also are able to autotomize their arms and regrow them.

Image 2: Feather star arm with tube feet extended.

An experiment done at the University of British Columbia, by Dr. Angela Stevenson, looked at the rates of arm regeneration in a local species of Feather star, and whether they are effected by climate change. Regrowth requires energy to form new cells and this may or may not depend on temperature, if the animal becomes stressed because of it.

What she found was that Feather stars in high temperature climates, had faster growth rates than those at the normal temperature, at which they are found in nature. This means that Feather stars in British Columbia, may actually be affected positively by increases in temperature caused by climate change.

Community Interactions

While this potential increase in temperature may positively impact regrowth in Feather stars, the surrounding community may be negatively affected. This is because, Feather stars produce feces that are usually high in calorie content at their normal temperature, and other animals stay by the Feather star and eat it. But at higher temperatures, the feces is lower in calories because the sea stars take up more nutrients from their food to supply energy for their fast regrowth.                           Image 3: Small crab waiting to feed on Feather star feces.

Now the creatures, like crabs and worms, relying on this food source won’t be getting as much energy, but the direct impacts of this are unknown. This example shows just how complicated climate change will impact individuals and whole communities, directly and indirectly through the food web.

 

 

Most of us have probably heard the word “cold-blooded” before, but do we know what it really means? You might think: “I’m human, so I’m warm-blooded, and that fish, it’s a fish, so it’s cold-blooded.” That thought process wouldn’t be incorrect, but when you get down to the nitty-gritty of it, ‘cold-blooded’ isn’t the best term to use. The blood of cold-blooded animals isn’t always cold, just sometimes, if their environment (whether that be the ocean or the land) is cold. The more appropriate term to use is ‘poikilotherm’,

poi·ki·lo·therm
/poiˈkēləˌTHərm,-kil-/

noun  ZOOLOGY

an organism that cannot regulate its body temperature except by behavioural means such as basking or burrowing

Poikilotherms include everything from frogs and snakes to the naked mole rat (a mammal!), and these days they are becoming the total opposite of ‘cold-blooded’ animals. What with the temperature of the earth on a precipitous upward trajectory, poikilotherms face a risk of mass extinction. (Warm-blooded vs. Cold-blooded: What’s the difference?)

For marine organisms, the effects of climate change are currently looking a bit more dire than their terrestrial counterparts. Poikilotherms have some leeway to the temperatures they can tolerate, but if their environment gets too hot (or too cold), they won’t survive. However, predicting how individual species will respond to climate change isn’t black and white. Last month I tested to see what had a stronger affect on shore crabs: long-term water temperatures or short-term (extreme) water temperatures. Using a local species of shore crab called Hemigrapsus oregonensis, I found out that, even if a crab lived its entire life in really cold water, it has no better chance of surviving a 30˚C heat wave than a crab that lived its entire life in warm water.

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However, the results of my experiment aren’t the be-all-end-all for these shore crabs. I only tested how quickly the crabs flipped over, and how long they took to start eating some food, so there are still lots of other factors to be tested, both behavioural and physiological, that will help predict how they will respond to climate change. I also mentioned before that it’s tricky to predict how individual species will respond to water temperature, and that’s because lots of species are so spread out across the earth that each population has its own unique adaptations to their environment. This becomes problematic when you consider that there are some species that are simply better at just about everything compared to any other species: feeding, mating, and surviving in unfavourable climates. For all species, including Hemigrapsus oregonensis, determining population-specific responses to thermal stress could be key for predicting how the marine intertidal ecosystem will look in 50 years. Will native species or non-native species fair better in the face of climate change? Will any poikilotherm do well? (See a comprehensive review here.) When considering Hemigrapsus oregonensis, in this dog-eat-dog world, who know which crab will win…

 

Sea anemones (uh-nem-uh-nee), not many know but during my presentation I had to really take the time to say their or names otherwise I’d sound just like Nemo!

For about 2 weeks, I had the opportunity to study sea anemones up close! Taking care of these creatures are hard, they’re super sensitive to a lot of things. This is why you should stay away from them and let them be on their own.

When touching them in the wild or in laboratory conditions, make sure you have clean hands! Soap, oil, metals and other contaminants even in small concentrations go a long way in changing their body conditions. The moment these guys get too stressed out they release this white/transparent mucus that gets all around them in the water column. This makes it harder for predators and perhaps you touching them to get a grip on them. However, depending on the mucus levels, if other sea anemones get a whiff of it (either physically, or through other sensory methods) they might stress out too! Now you got a big group of them all freaking out!

Sea anemones are closely related to jellyfish and have poisonous cnidocytes (similar to a poison dart) in their tentacles. Most of the sea anemones that live here in Vancouver in shallow waters are okay to touch. Their cnidocytes arn’t strong enough to puncture human skin. But always be cautious! However, the big tropical ones especially Hell’s Fire anemone, and the Carpet anemone living in the Indo-Pacific are harmful to humans. The sting from Hell’s Fire can give skin ulcers and the Carpet anemone’s sting can send you into organ failure. Those are to not mess around with! Someone has been stung and has lived to tell the tale, just ask our professor Chris, who one day decided to lick an anemone in the tropical oceans — must have been in the name of science!

 

 

 

 

 

 

 

 

Mother nature always has exceptions up her sleeve. There are some species that can live happily with some of the sea aneomes. Nemo for example can! Clownfish are coated in a specialized mucus which allow them to go live within the sea anemone without being attacked. It’s been seen that these clownfish bait other fish into the tentacles of the anemone. Talk about a cool partnership!

More a fun video to watch on the symbiosis between clownfish and sea anemones, check: https://video.nationalgeographic.com/video/clownfish_amonganemones

 

 

 

Kyle (Interviewer):          Hello everyone, and welcome back to the “Snailing It!” podcast, the show where we interview invertebrates who are at the top of their game. I’m Kyle, your host with the most, and today we have a very special guest. You may know him for his striking zebra-like shell stripes, or recognize him from his recent appearance on ‘Dancing with the Sea Stars’… please welcome two-time water polo world champion, Sheldon Natalensis!

Sheldon:          Thanks Kyle, pleasure to be here… big fan of the show.

Kyle:          Now Sheldon, first off, congratulations on your recent win against ‘Urchins United’. Amazing game.

Sheldon:          Yeah thanks Kyle, they put up a great fight, but we were able to clinch the win in the last couple of minutes there.

Kyle:          What a shell-biter. So, we’ve brought you on the show today to talk about your amazing career in water polo. Tell me, how did you first get into the game?

Sheldon:          Y’know, I’ve always been an active snail. I grew up in a pretty warm place, usually between 22 and 26 degrees [Encyclopedia of Life: Neritina natalensis], so me and my buddies were out playing in the freshwater intertidal zone year-round. In Shellementary school, I joined the water polo team, and it kinda progressed from there.

Kyle:          I understand you faced a bit of criticism when you first started playing at the professional level… what was that about?

Sheldon:          Yeah, tropical organisms like me get a bad rap, because we don’t have as high a tolerance for temperature change [Vinagre et al., 2016]. With the way things are going out there, a lot of value is placed on your ability to acclimate or adapt to changes.

Kyle:          On that note, what’s your personal experience with the changing global climate?

Sheldon:          I’m lucky to live in the tropics, Kyle, because the warming here is nothing compared to changes further north [State of the Climate 2016]. Although, they say that our metabolic rates will change by the same amount as the north, but with a smaller change in temperature [Dillon, Wang, & Huey, 2010], so I’m a little worried about the long-term implications of global warming in that sense.

Kyle:          Yeah, I think we’re all a little worried about that.

Sheldon:          It’s a scary world out there for an ectotherm, Kyle!

(laughter)

Kyle:          So, I know top-level invertebrate sports can get pretty intense… how do you handle the pressure?

Sheldon:          Y’know, I do my best to stay calm. Even with changing temperatures, I try to keep my oxygen consumption rate steady. That way, even if you’re stressed out, no one can tell. It’s helped a lot with my ability to cope with changes in my environment.

Kyle:          What do you have to say to all the little invertebrates out there who want to play professional water polo?

Sheldon:          Well Kyle, my best advice would be to not let changing conditions get to you. Keep behaving like you would in your normal temperature range, and things will all work out… Or at least that’s what worked for me!

(laughter)

Kyle:          Well, it’s been a pleasure talking to you, Sheldon. Best of luck in the upcoming Pacific Ocean Finals!

Sheldon:          Thanks, Kyle. I appreciate it.

Kyle:          And to all of you listening at home, thank you for tuning in to “Snailing It!”. For any of you interested in how the global climate has changed over the last few centuries, I suggest you check out this cool video put together by NASA.

NASA Climate Time Machine

Kyle:          Join us next week, when we talk to Clara Lamellosa, marine snail weightlifting champion, about her experiences with acute temperature change. For now, this is Kyle Gastropoda, signing off.

They’re dark purple, slimy, and ravenous worm-like predators, and they come by night. When the tides recede, they emerge from the mud on the hunt for flesh. Upon contact, a toxic orange tentacle shoots out to entangle the hapless victim who soon stops struggling and gets devoured whole. It’s the very stuff of horror movies and yet this is alien creature is a very commonplace inhabitant of the intertidal here in Vancouver, called a ribbon worm.

 

All ribbon worms share a similar proboscis apparatus with which they hunt. This tentacle-like appendage is formed from an infolding of the body wall, and can extend almost the entire length of the worm. When it contracts, the fluid in the sheath surrounding the proboscis experiences pressure that forces the tube to turn inside out and extend. A dart at the end can inject paralytic toxins, and sticky mucus secretions help ensnare prey, turning these unassuming worms into fierce predators.

 

An example of a ribbon worm in the lab. Note the massive mucus production and extensive proboscis. This specimen was roughly 20 cm long.

 

If you happened to pass by Jericho Beach on a Sundays, you might have seen me and wondered why anyone in their right mind would bring chopsticks beachcombing; through trial and error, I found that this most effective for handling these slimy creatures. Initially, I was fascinated because we know so little about them. We do know that their mucus is toxic and that they are extremely unappetizing as prey, so I wondered what other sorts of things do affect them, and the obvious answer was climate change!

 

In the lab I investigated the effects of global warming and ocean acidification by keeping some of the worms in acidified seawater (pH 7.4, control = 7.8-8.0) for a week and then heating half of both the acidified and normally treated worms at 30˚C over 4 hours. Very few people have looked into how performance in these worms gets affected, so I had to come up with a response, and what cooler (and more intuitive) to look at than feeding response! Essentially, I stimulated (poked) the worms with a dead specimen of the sandworms they eat, using masterful chopstick skills, to provoke an eversion.

 

I found that both of these effects of climate change decreased the likelihood of ribbon worms feeding, possibly in a mechanism to conserve energy, or because they were just stressed and not performing well. It also seemed that a combination of these stressors affected performance more strongly, although much more work needs to be done in this direction. Scary though they might be, by eating sandworms, these ribbon worms may be doing important pest control in the intertidal by slowing algae consumption. They are gardeners that help maintain the balance and health of coastal ecosystems and we should definitely keep looking into how they will be affected by climate change since this will have cascading implications for the entire intertidal.

 

A graph showing the proportion worms in each treatment condition that successfully everted its proboscis within 5 stimulations. 25 worms were tested in each case, except in the pH treatment which had 28.

 

To see an epic battle between ribbon worm and sandworm, like what I tried to stimulate in the lab, check out this video:

https://www.youtube.com/watch?v=EwcEYAGu07E

Does this lake speak to you? Image obtained from https://www.greenandgrowing.org/what-is-eutrophication/

Or how about this waterfall? Image obtained from https://www.dreamstime.com/stock-photo-turbid-water-tropical-waterfall-hard-rain-image9235670

Neither of these freshwater bodies look very inviting, right? If we wouldn’t want to even dip a toe in it, I can’t imagine the animals living in there are enjoying their afternoon swim either. We have the choice of not jumping in for a swim, but the same can’t be said for the organisms that call these habitats their home. Unfortunately, these are common phenomenons nowadays due to various human activities. Deforestation, urban development, wastewater discharge, the list of activities that degrade water quality goes on and on.

Eutrophication, which is caused by excess nutrients in the water, still happens often in lakes and rivers across the world, despite a reduction in nutrient loading since the 60s/70s. Changing land use is also causing increased sedimentation as surface runoff erodes soil, carrying sediment with it and depositing it in freshwater systems. Both of these occurences are highly problematic for the ecosystem, you can learn more about that here and here.

For my independent project, I decided to test how organisms would respond to increased nutrient concentration and turbidity in the water. I did this with Daphnia pulex, a common species of water flea ubiquitous to freshwater habitats. It is a microscopic zooplankton that feeds mainly on phytoplankton, and it is an important food source for many other trophic levels, especially fish.

A cute lil water flea! Image obtained from http://snakesafe.jalbum.net/Micro-life%20III/slides/IMGP4451%20daphnia%20pulex.html

I had 4 treatments with different water conditions: control, eutrophic, turbid, and eutrophic and turbid combination. For the eutrophic treatments, I added known concentrations of nitrate and phosphate to the water. For the turbid treatments, I scooped up some mud from a storm ditch and added a few squirts to the water.

Different water treatments for my D. pulex subjects to live in. Photograph by me

Then I transferred 10 D. pulex individuals into each beaker and let them acclimatize for 24 hours. After that, I placed each individual on a Petri dish under a microscope. I counted the number of heartbeats within the span of a minute, and compare average heart rates between treatments.

The heart (and other body contents) of a water flea is easily visible thanks to their transparent shell. Image obtained from https://phys.org/news/2016-07-scientists-fleas-territory.html

I predicted that the elevated concentrations of nutrients and sediment particles in the water would stress the water fleas and increase their heart rate. My results showed that eutrophic water and turbid water did result in a higher average heart rate compared to the control. However, the combination of eutrophic and turbid water did not really have an effect, and there is likely an interaction between those factors that influence heart rate in some way. It seems like eutrophication has different consequences on heart rate depending on the turbidity of the water, and it would be interesting to do further research on this. Aspiring honours students take note!

What I imagine the water fleas’ hearts doing during the experiment. Meme created by me

What a stressed out water flea actually looks like. The heart is the translucent fluttering sac located behind their tube gut. GIF generated by me

This experiment was interesting and informative, and the results gives us insight on how other organisms would respond to similar conditions. Because Daphnia are also keystone species in the ecosystem, they could be used as indicators for pollution levels if further ecotoxicology studies like these are conducted. It is important to determine their tolerance to changes in the environment, because without Daphnia, the food web might be thrown out of balance.