Designing a lab

My ecological concern is the bleaching of corals due to rising ocean temperatures. The excess carbon dioxide we release into the air from burning fossil fuels mixes with the ocean water and makes carbonic acid. This reaction creates heat energy, which causes the ocean temperature to rise. Because of this, the zooxanthellae present in corals (the organism that gives the coral food and gives it it’s colour) gets expelled from the coral tissue. Since zooxanthellae provide the coral with food and colouration, the coral starts to starve and turns white. I have done some reading during this course, and have established that coral can bleach at one degree Celcius over the average temperature of its habitat. However, I have not found anything on the amount of time it takes for coral to bleach. This made me very curious and greatly inspired this experiment. The goal of this lab is to try and pinpoint the amount of time it takes for zooxanthellae to be expelled from the coral tissue at various specific temperatures.

Lab question

How much time and at what temperature does coral bleaching occur?

Hypothesis

Based on my previous research, I believe that corals will bleach at one degree over the average temperature of the ocean. I estimate that I will see a difference in zooxanthellae levels present in the corals within a week of the experiment.

Materials

4 see-through tanks filled with ocean water
4 samples of live healthy coral (with a diameter of approximately 20 cm each)
4 programmable aquarium heaters
4 oxygenators
1 microscope and standard microscope equipment (slides, Petri dishes, etc.)
1 Water sampler

Procedure

1- Connect the oxygenators and aquarium heaters to each tank. Set one tank to have a temperature similar to the one it is used to (water temperature in its home reef). Then, set every other tank to be one degree higher than the last.

2- Place one coral inside each tank. Make sure all of the corals are similar in size, shape, and state of health. Ideally, they all came from the same skeleton.

3- Write down your visual observations of each coral (how much they have bleached) in the observation table. It’s fine if there are no visual differences so far; you still have to write it down in the daily observation chart. Take pictures so you can compare them later on.

4- Take a water sample from each tank and pass the water samples under the microscope. How many expelled zooxanthellae are there? It’s okay if there are none so far. Write everything in your daily observation table. Write any additional notes you have in the table as well.

5- Repeat steps 3 and 4 every day of the experiment. In my opinion, this experiment should last around a month to get the most amount of information. This length can always be shortened by the experimenter if they already have enough data to answer the lab question or can be lengthened if they do not have enough.

Observation table (To be repeated every day of the experiment)

Possible sources of error

One possible source of error is if the temperature of the room that the coral tanks were in was higher than their desired temperatures. The temperature of the room should be set to one degree lower than the tank with the lowest temperature.

Another possible source of error is if the corals are not similar enough in size, shape, state of health, type of coral, etc. As I have mentioned earlier, they ideally all come from the same coral skeleton.

DISCLAIMER: I am NOT a Profesional, I am a student. This entire experiment is hypothetical.

Photo of zooxanthellae by dugongs4fr on Flickr