Chillin’ with Shore Crabs

The Earth is warming at an unprecedented rate due to the input of greenhouse gases (like carbon dioxide) to the atmosphere by human activities. However, there is a lot more to global climate change than most people realize. Did you know that the weather in some parts of the world is going to get hotter, but also a lot more variable1? Or that increased carbon dioxide emissions are increasing the acidity of the ocean1? (This process is termed “ocean acidification”).

North America is expected to experience an increased frequency of storms and cold-snap events. These additional stressors make studying the impacts of climate change on intertidal systems difficult. It is important to address the interaction of these concurrent stressors to determine how they will affect organism functioning.

Crab-lover in the wild. Photo credit: Jaime Grimm

Crab-lover in the wild. Photo credit: Jaime Grimm

All organisms have a range of temperatures between which they can survive and function. Beyond this range, ecological performance of organisms is lost. For example, when shore crabs get too cold they enter a state of “chill coma” where they become temporarily immobile, but fully recover once the temperature increases. Inversely, when shore crabs get too hot, they begin having muscle spasms and cannot control their movement. Either of these responses can be detrimental to crabs’ survival because it hinders their ability to forage for food or escape predators looking for an easy snack. Climate change may increase the occurrence of conditions that cause these responses in shore crabs. What does the future look like for shore crabs then? Will climate change be the end of our local pinch-beasts2?

Hemigrapsus oregonensis in chill coma. Photo credit: Jaime Grimm

Hemigrapsus oregonensis in chill coma. Photo credit: Jaime Grimm

I tested the impact of ocean acidification on shore crabs’ (Hemigrapsus oregonensis) ability to tolerate extreme temperatures, above and below their thermal optimum. My hypothesis was that increased acidity of water would create a stressful environment for crabs and would narrow the range of temperatures they are able to tolerate before their ecological performance is lost.

A different species of shore crab (Hemigrapsus nudus) enjoying the sun in Bamfield, B.C. Photo credit: Anna Cappiello

A different species of shore crab (Hemigrapsus nudus) enjoying the sun in Bamfield, B.C. Photo credit: Anna Cappiello

Fear not, crab-lovers! I was pleasantly surprised at how resilient our little crustaceans can be. Acidic waters didn’t seem to impact crabs tolerance of cold temperatures at all! Additionally, acidic water actually seems to make crabs more tolerant to warm temperatures. Why?

My best guess is that acidic water induces the production of “heat-shock proteins”3. These proteins are produced by organisms under stressful environmental conditions to help stabilize performance on a cellular level4. So, maybe crabs will do okay under climate change conditions, but additional research and time will tell.

  1. 2014. Climate Change 2014: Impacts, Adaptation and Vulnerability. Summary for Policymakers.
  2. Credit to Dr. Christopher Harley for creating the nickname “pinch-beasts” for our shore crabs. How fitting!
  3. Cummings, V., Hewitt, J., Van Rooyen, A., Currie, K., Beard, S., Thrush, S., Norkko, J., Barr, N., Heath, P., Halliday, N.J., Sedcole, R., Gomez, A., McGraw, C. and Metcalf, V. 2011. Ocean acidification at high latitudes: Potential effects on functioning of the Antarctic bivalve Laternula elliptica. PLoS ONE, 6(1): 1-11.
  4. Lindquist, S. 1988. The heat-shock proteins. Annual Review of Genetics, 22: 631-677.
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