A Heartwarming Tale. Literally

The end of the semester in UBC’s Experimental Biology of Invertebrates class means it’s time for students to start working on their independent projects. What does an independent project entail, you ask? Well, it could be an almost infinite amount of things. This year we saw experiments examining the many different behavioral or physiological characteristics of several interesting creatures such as anemones, mussels, crabs, and even barnacles, just to name a few. For my own independent project I took a look at how global warming relates to the metabolic activity in green shore crabs.

As most of us are probably aware by this point, global warming is an ongoing phenomenon that is reshaping the environments on Earth, both on land and under the water. Average temperatures around the world are on the rise, and many predictions estimate that this trend will continue into the unforeseeable future. This has the potential to spell disaster for creatures living in the intertidal zone where the increase in temperature, and the decrease in local salinity due to heavy rainfall and melting ice is more prominent.

To examine how these environmental factors affect the basic physiology of green shore crabs I set off on a journey down to Tower Beach in order to collect some lucky individuals. Once I’d gathered up enough specimens I brought them back to the lab and began setting up my experiment by acclimating the crabs in containers with various conditions. Half of the containers contained seawater at approximately 13°C (the average temperature of the ocean water in Vancouver), and the other half of the containers contained seawater that was allowed to warm up to room temperature, which was approximately 20°C. For half of the containers in each group (13°C or 20°C) I diluted the seawater with distilled water such that they were at 50% regular salinity. I allowed the crabs to remain in these containers for 48 hours before I returned to subject them to the wrath of science.

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Crabs acclimating in their containers.
Photo credit: Jon Howe

The next phase of the experiment involved moving the crabs into little plastic cups filled with their container water. I then sealed the cups with plastic wrap and elastic bands and left them alone for another 24 hours. When I came back to the lab the following morning I measured the pH in each cup. Why, you might ask, did I measure pH as an estimation of metabolic rate? Because during cellular respiration an organism consumes oxygen and produces carbon dioxide. This carbon dioxide then reacts with water to Hydrogen and Bicarbonate ions, which are both acids that lower pH. The logic is that a higher metabolism leads to more carbon dioxide, which in turn leads to a lower pH. So what did I find after all this work? A whole lot of nothing, mostly. It is widely known that higher temperatures lead to an increase in metabolic activity in cold-blooded organisms, and that was the only variable that had any significant effect on my crabs. Sadly, the salinity that I tested was either not low enough to affect the crabs, or I included too few crabs in my experiment to statistically prove that salinity has an effect on metabolism. Better luck next time I suppose.

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(almost)Solitary confinement. Crabs hanging out in their plastic cups for the day.
Photo credit: Jon Howe

To learn more about global warming, check out this informative video:
https://www.youtube.com/watch?v=xcVwLrAavyA

To learn more about the metabolic activity of cellular respiration, please follow the following link:
http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CellularRespiration.html

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