It’s finals season, and the stress seems to be apparent in all of my classmates and myself. But I wondered whether some of our rocky intertidal friends would also show signs of stress. And so, when given the opportunity to design and carry out my own experiment these past couple of weeks in BIOL 326, I decided to test this!
Since organisms living in the rocky intertidal are not exposed to the same daily stress as you and me, I decided to define stress as the stress of ocean acidification.
Ocean acidification is due to increased carbon dioxide gas in the atmosphere; the carbon dioxide gets taken up by our oceans and causes a chemical reaction, increasing hydrogen ions in the water. Thus the pH decreases, causing acidification, because pH is a measure of the amount of hydrogen. If you want to learn more about the physical manifestations of ocean acidification check out this link for some shocking photos.
In order to test this stress, I used the green shore crab, Hemigrapsus oregonensis. It is a great study organism, because it is easy to collect and lives in a stressful environment, the rocky intertidal. One can tell the difference between male and female just by turning them over, so I was able to also test whether males or females reacted to stressors differently.
I put some crabs in a treatment condition with a normal level of carbon dioxide and some crabs in a treatment condition of a higher level of carbon dioxide. After leaving them alone for a week, I then tested to see if they could handle an additional stress! I tested the effects of very high
temperatures and low salinities on them to observe whether or not having been exposed to high carbon dioxide would affect their reactions to these additional stressors.
What I found was that despite if they were in high or low carbon dioxide, and despite if they were male or female, there were no difference in their tolerance of high temperature. This could mean that perhaps they were not stressed by the carbon dioxide nor the combination of being exposed to high carbon dioxide and high temperature. In addition, I found that crabs kept in the elevated carbon treatment, regardless if male or female, were able to tolerate a lower salinity than their normal carbon treatment counterparts! This suggests that they either could tolerate both stressors, or that the elevated carbon stressed them out to a point where their senses were unable to detect the low salinity.
In addition to all of the experimentation, I did notice that they were behaving in a very odd way. A fellow classmate and I named this behaviour as a “Barrel of Crabs”. The crabs kept in the high carbon were acting very strangely because they were all holding on to each other, as if for dear life! I was unable to pry them apart without damaging them.
Basically from my experiment, I learned that they were either stressed or they were not, and in science it is usually the case to have two opposite explanations. There is one thing I am sure of from my experiment though, and it is that I need to do further experiments! Despite the mixed results, I enjoyed being able to work on a project on my own and deciphering what the results could potentially mean.