It isn’t only humans that have to deal with too much stress

Imagine that you have just had a long stressful day at work, and then as you are leaving, you find out that your car has broken down, and you are already running late for an event. It is a common everyday situation that stress tends to pile up on a person. But what about other organisms? While they don’t necessarily have a job to go to or bills to pay, other organisms experience stressors daily as well.

The Green Shore Crab, Hemigrapsus oregonensis, Photos: Heather Bryant

The Green Shore Crab, Hemigrapsus oregonensis, Photos: Heather Bryant

Take the green shore crab for example. They experience many abiotic stressors, including daily fluctuations in their intertidal environment due to the tide going out, leaving them exposed to air, and then coming in again, submerging them in water. Additionally, they, along with other organisms, are exposed to long-term stressors in the face of global climate change.

Many people are familiar with the threat of increasing global temperatures, but accompanying this are the threats of ocean acidification, more frequent extreme weather phenomena, and changes in ocean salinity. The most important thing to consider is that none of these are occurring in isolation.

For my independent project in Biology 326, I sought to investigate the combined effects of increased temperature and low salinity on the green shore crab’s performance. In order to do this, I acclimated the crabs to different combinations of temperature (ambient or high) and salinity (ambient or low). I then placed them in seawater and gradually increased the temperature to see just how high of a temperature they could tolerate before showing signs of stress. This was a measure of their thermal tolerance.

Left: high temperature acclamation chambers, one at low salinity and one at ambient salinity, Right: set up for determining thermal tolerance, Photos: Heather Bryant

Left: high temperature acclamation chambers, one at low salinity and one at ambient salinity, Right: set up for determining thermal tolerance, Photos: Heather Bryant

Interestingly, I found that when exposed to both high temperature and low salinity stress, the crabs were unable to cope with the same high temperatures they were able to tolerate when exposed to only one of these stressors. However, I found that the crabs had the highest thermal tolerance when they had only been acclimated to high temperatures.

FINDINGS

Summary of findings

Hence, the impact of increasing temperatures on the green shore crabs may be different depending on whether they are also exposed to low salinity stress or not. Considering green shore crabs around Vancouver experience low salinity during the summer months with the Fraser River runoff, this could be bad news for them. This makes me wonder, what happens if they also have to deal with ocean acidification on top of this?!

So just like you and I, crabs and other organisms will probably not be able to perform as well if they have multiple things stressing them out. If they cannot perform as well, this may leave them open to predation, or other harm. In turn, this could end up changing their interactions with other organisms and eventually influence how the ecosystem they are in functions.

To learn more about the green shore crab, check out this website: http://www.wallawalla.edu/academics/departments/biology/rosario/inverts/Arthropoda/Crustacea/Malacostraca/Eumalacostraca/Eucarida/Decapoda/Brachyura/Family_Grapsidae/Hemigrapsus_oregonensis.html

To learn more about the changes that accompany global climate change, check out this website: http://www.epa.gov/climatestudents/impacts/signs/index.html

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