Elia Viot & Charlotte Roy

Age 15 | Chelsey, QC & Ottawa, ON

Winners of the Saint-Joseph College science fair (Hull) | Winners of the Outaouais regional science fair | Finalists at the Quebec provincial science fair

INTRODUCTION

Ocean acidification is a global environmental problem that is becoming more and more relevant. “The carbon dioxide present in the atmosphere (coming from, among other sources, fossil fuels, industrial activities, and the general population) dissolves in the ocean. This lowers the pH, rendering it (the ocean) more acidic” (translated from Osterloff, 2017). In fact, the oceans’ acidity has increased about 30% since the beginning of the industrial revolution. Unfortunately, the long-term consequences of the phenomenon (such as the impact on coral reefs, marine life, and marine ecosystems) are unclear and there isn’t really an effective way to diminish the acidity of the oceans except, of course, by reducing global CO2 emissions. However, this problem, as we will show through our experiment, affects not only marine animals, but could eventually severely affect Earth’s entire population.

GOAL

Our goal is to determine and understand the effects of ocean acidification on marine life. To determine the consequences of ocean acidification, we will conduct an experiment with eight sealed containers containing mussel and oyster shells. Four of these will contain salt water with a pH identical to the ocean’s current pH (8,1), and the other four will contain salt water with a much more acidic pH (around 5,5). The containers will be stored at different temperatures. After one month, we will open the containers and check the results.

HYPOTHESIS

We believe that the ocean acidification will cause the mollusc shells to degrade, and could put certain marine species at risk. In fact, according to the Government of Canada, ocean acidification could cause a reduction in growth rates and an increase in mortality in certain marine species (Pêche Canada, 2018). Therefore, we believe that the shells in the containers with a more acidic pH will be the most affected. Furthermore, we think that the algae could help to diminish the water’s acidity, since according to biologist Colleen Musialski, certain types of algae can eliminate carbon dioxide from water (Musialski, 2018). We can verify our hypothesis by analyzing the results we obtain after our experiment.

MATERIALS

For our experiment, we used a 200g (± 0,01 g) scale, a pH-meter, un bucket, a spoon, a hammer, paper towels, a metal fork, a penny, 8 Mason jars and 8 airtight metal lids, and a camera to take photos throughout our project. We also used the following substances: oyster and mussel shells, filtered water, Instant Ocean sea salt, and white vinegar.

PROTOCOL

Sea water preparation
To make the sea water, we mixed in the bucket the recommended dose of Instant Ocean salt with filtered water. Then, we measured the pH of this mixture with the pH paper, ensuring that it was around 8,1, since it’s the current ocean pH. To reach the desired pH, we added water or salt.

Preparation of the neutral containers
Firstly, we rinsed and dried all the shells. After that, we broke the shells with the hammer so that they were slightly bigger than a 25¢ coin, and weighed them, ensuring to note the exact weight (each container had around 30g of shells). After having photographed the shells, we transferred them to a Mason jar, poured sea water into the Mason jar until it was full, and sealed it with the metal lid. If there had been any space left between the solution and the cover, CO2 could have escaped, which would have rendered the experience inconclusive. Finally, we repeated this process for the 3 other Mason jars. There are two neutral containers for each type of shell.

Preparation of acidic containers
For the acidic containers, we followed the same steps for the neutral containers. However, after having put the shell fragments in the containers we added 3 drops of vinegar and mixed well. Then we waited a few minutes, after which we measured the pH of the solution with pH paper, ensuring that it was around 5,5. If it was not 5,5, we added sea water or vinegar to reach the desired pH. Finally, we sealed the jar with the metal cover and repeated the process for the 3 other acidic containers.
For each type of shell, we kept a neutral container and an acidic container in the refrigerator to observe the effect of temperature on shell decomposition. A description of the 8 Mason jars used in the experiment (4 neutral containers and 4 acidic containers) can be found in appendix 1.

Evaluation of the results after a month
After a month, it was time to discover our results! We opened each Mason jar and emptied the water over a sieve. Then, we rinsed and dried the shell pieces with paper towels. For each jar, we made sure to weigh the shells, take note of the weight, and take a photo to compare their general appearance before and after their time in the jars. Then, we tested the hardness of the shells with a metal fork and a coin. Finally, we compared all of our results.

RESULTS

**Table 1**: Weight of the mollusk shells after 3 weeks in the jars of water according to jar type

**Table 2**: Appearance of the shells and the water after 3 weeks in the jars of water according to jar type
**Legend**
*Water transparency :*
1 = Completely opaque
2 = Very cloudy water, many small pieces and particles
3 = Slightly cloudy water, a few small pieces and particles
4 = Clear enough water, a few impurities
5 = Clear and transparent water
*Similarity to previous appearance:*
1 = Completely different appearance (different colour, shape, and texture)
2 = Different appearance (some different spots of colour and shape slightly changed)
3 = Slightly different appearance (a few small differences in colour and shape)
4 = Generally similar appearance
5 = Appearance identical to previous appearance

INTERPRETATION

The goal of our project was to understand and demonstrate the consequences of ocean acidification on marine life to determine which solutions would be the most efficient. This equation shows that carbon dioxide and water together form carbonic acid, which renders the oceans more acidic:

CO₂ + H₂O ↔ H₂CO₃

The results obtained show that in general the shells weighed more after the time they spent in the Mason jars. We think that this is due to the fact that they started calcifying. “Calcification is the normal or abnormal process during which the organism’s tissues harden due to a calcium salt deposit” (translated from Doctissimo, 2019). The salt in the jars would have reacted with the shells, which would have started to form a thicker shell. This is why they became heavier.

The main differences were that the shells in the non-acidic jars looked healthier and dissolved less than those in the acidic jars. This can be explained by the fact that ocean acidification particularly affects shells made of calcium carbonate (such as oyster and mussel shells). The more acidic the ocean is, the faster the shells dissolve. Animals with a calcium carbonate structure therefore have to sacrifice more time repairing and reinforcing their shells to survive. In fact, as is shown in table 2, the appearance of the non-acidic shells after was very similar to their appearance before, whereas the shells in the acidic jars had changed colour, and were less bright and shiny (see appendix 1 for before photos and appendix 5 for after photos).

Furthermore, the oysters in jars 1 and 3 (neutral and acidic, 20℃) smelled like a sewer. We can explain this by the decomposition of the shells, which were poorly preserved at room temperature. In fact, the jars stored in the refrigerator did not show any signs of mold. The decomposition would have released sulfur, which explains the bad smell (an oyster shell containing sulfur: “consists of organic matter and traces of manganese, iron, aluminium, sulfate, and magnesium” (translated from Bryant, 2018). However, the acidic jar (3) smelled the strongest, which proves that acidity increases the decomposition process.

We can confirm our original hypothesis, which was that the shells in the acidic containers would be the most affected. According to the Natural History Museum in London: “marine life is menaced by the rise in acidity. The organisms who have carbonate calcium shells or skeletons are already affected and their shells are starting to dissolve” (translated from Osterloff, 2017).

The excess carbon dioxide is the source of the rise in acidity in the oceans, so algae cultivation is a perfect solution to reduce this gas, since algae performs photosynthesis. Algae can also be used to create biogas and be used as fertilizer. We can also eat them, and they filter water very efficiently.

We could bring about some modifications to our projects. To weigh the shells, we did not use the same scale before and after, which could be an error source for the results that were obtained. Moreover, we could have increased the acidity in the jars even more to obtain more significant results in a short time period.

CONCLUSION

Our goal was to determine and understand the effect of ocean acidification on marine life. We discovered that ocean acidification causes deterioration and calcification of mollusk shells. In fact, the shells in acidic water had changed colour and appearance. Our project is innovative because it allowed understanding of the effects of acidification and showed them on a small scale, which helps us find solutions for the future.

REFERENCES

Bennett, J. (2018, April). Ocean acidification. Smithsonian. https://ocean.si.edu/ocean-life/invertebrates/ocean-acidification

Bryant, J. (1985). Skeletal materials- Biomineralization: The oyster. Yale- New Haven Teachers Institute. https://teachersinstitute.yale.edu/curriculum/units/1985/7/85.07.02.x.html

Doctissimo. (2018, November 19). Calcification. https://www.doctissimo.fr/sante/dictionnaire-medical/calcification

Enve Class. (2018, October 16). Ocean acidification, “The evil twin of global warming”. Energy and Environmental Policy 2018. https://eepolicy2018.wordpress.com/2018/10/16/ocean-acidification-the-evil-twin-of-global-warming/

Maranowski, M. (2020,June 23). Swimming in acid: Understanding ocean acidification. Science Buddies. https://www.sciencebuddies.org/science-fair-projects/project-ideas/OceanSci_p013/ocean-sciences/ocean-acidification

Musialski, C. (n.d.) Can marine algae change with the climate. Ask a Biologist. https://askabiologist.asu.edu/plosable/algae-ocean-acidification

NOAA. (n.d.). What is ocean acidification?. https://www.pmel.noaa.gov/co2/story/What+is+Ocean+Acidification%3F

Osterloff, E. (2017). What is ocean acidification? Natural History Museum. https://www.nhm.ac.uk/discover/what-is-ocean-acidification.html

Paris, G. (2019, June 7). L’acidification des océans, l’autre danger du CO2. The Conversation. https://theconversation.com/lacidification-des-oceans-lautre-danger-du-co-114716

Pêches et Océans Canada. (2018, December 3). Qu’est-ce que l’acidification de l’océan?. https://www.dfo-mpo.gc.ca/oceans/publications/soto-rceo/2012/page02-fra.html

Québec Océans. (2018, January). L’acidification des océans (publication nº4). Université Laval. http://www.quebec-ocean.ulaval.ca/pdf_xls_files/Fiche4.pdf