One crab’s response to ocean acidification

Climate change is often discussed in terms of its atmospheric effects, but increased carbon dioxide levels are also having an impact on the ocean. Carbon dioxide is absorbed by the ocean and a chemical reaction in the water results in ocean acidification. Human involvement in increased atmospheric carbon dioxide includes the burning of fossil fuels and deforestation.

Atmospheric carbon dioxide levels are increasing, which leads to more carbon dioxide being absorbed by the ocean. Carbon dioxide binds to water producing carbonic acid that dissociates to hydrogen and bicarbonate ions. A higher concentration of hydrogen ions means that the water is more acidic and has a lower pH. This process is known as ocean acidification. Diagram credit: Spikko

Marine animals are sensitive to changes in their environment such as the decreased water pH due to ocean acidification. Our experiment this week focused on the effects of ocean acidification on the recovery time from chill coma of green shore crabs (Hemigrapsus oregonensis).

The green shore crab. Photo credit: Marietta College

Green shore crabs, the familiar crabs that you find underneath rocks at the beach in British Columbia, are ectotherms, which means that their internal temperature is determined by the temperature of their environment. At a low temperature, known as the thermal critical minimum, the crabs stop moving and enter “chill coma”. We measured the crabs’ recovery times from chill coma by cooling the crabs in an ice water bath until they stopped moving and recording the time that it takes for the crabs to right themselves once they have been removed from the ice bath and placed on their backs. Recovery time from chill coma is a proxy for an animal’s ability to tolerate cold. We measured the recovery time for two sets of crabs. One set, the control group, had been left in unaltered sea water for one week. The other set, the experimental group, had carbon dioxide bubbled into the sea water that they were left in for one week, which reduced the water’s pH. We learned from the results of our experiment that crabs which had been exposed to low pH conditions had a faster recovery time than the control crabs and thus are more cold tolerant.

The results of our experiment demonstrate that ocean acidification has an effect on marine invertebrates. Climate change will have an effect on the marine ecosystem and will alter it in ways that we cannot fully predict due to the many interactions of biotic and abiotic factors. Our green shore crab experiment is just one example of how a marine animal will respond to ocean acidification.

To reduce your contribution to global climate change and ocean acidification you can reduce your carbon dioxide emissions by driving less and reducing your use of paper. Driving less helps because the burning of fossil fuels, such as gasoline, produces carbon dioxide that enters our atmosphere contributing to climate change. Reducing your use of paper helps because our forests are an excellent carbon sink, trees remove carbon dioxide from our atmosphere and release oxygen, so carbon dioxide is absorbed by trees instead of the atmosphere or the oceans. Walk, bike, take transit and car pool when you can, this will reduce the amount of fossil fuels that you burn, reducing the amount of carbon dioxide that you emit to the atmosphere. Cut down on your use of paper, print-double sided, hand in assignments electronically, read the newspaper online, and use hand dryers instead of paper towels, because this will reduce the demand for paper which will reduce deforestation for paper products. Click here for more suggestions on how to reduce your carbon footprint. Being conscious of your contribution to global climate change and making small changes will help to reduce the future impacts of climate change which can help ensure that species like the green shore crab thrive.


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