Rapid increases in carbon dioxide (CO2) emissions into the atmosphere as a result of intensified anthropogenic activities are altering seawater chemistry at unprecedented rates. As a sink of anthropogenic emissions, the increasing amount of dissolved CO2 in the ocean forms carbonic acid (H2CO3). This increase in acidity triggered a pH decline of sea surface water and is expected to decline by an alarming rate of 0.45 units by 2100 (Jin et. al, 2021). Many marine creatures are extremely sensitive to these changes, with ocean acidification postulated to have caused mass extinctions and ‘reef gaps’ during the Paleocene-Eocene Thermal Maximum (Shi et. al, 2016). Therefore, ocean acidification are extremely harmful to marine organisms as they disrupt the acid-based physiology in these creatures, triggering lowered calcification rates in many shell-forming marine organisms.

Mollica, Guo, Cohen and Solow (2018) demonstrate how coral reefs in particular are especially sensitive to ocean acidification as it reduces the amount of calcium carbonate (CaCO3,) aragonite, that are fundamental for coral skeleton growth. Rising atmospheric carbon dioxide also causes severe heat stress which triggers coral bleaching events, presenting a conundrum for coral growth as the longer time a reef is protected from heat stress, it becomes increasingly vulnerable to ocean acidification effects which severely compromise the successful fertilisation and survival of coral reefs. Therefore, if humankind is to continue its ‘business as usual’ approach towards emissions, it will not be long before coral reefs eventually erode and become extinct. This is a disastrous consequence for the world as they are critical marine ecosystems (an estimated 1 million species depend on coral reefs), protect coastal areas and channel multiple ecological and economic benefits (Jussen, 2022).

Apart from corals, ocean acidification can aggravate the toxicity of heavy metal pollutants such as Cadmium (Cd), posing severe health risks for marine organisms that unknowingly ingest these contaminants. The employment of Cadmium in agricultural and industrial activities has culminated in substantial Cadmium concentrations in marine environments. As it is more soluble than other pollutants, Cadmium is easily accumulated by marine bivalves (oysters). The ingestion of Cadmium has deleterious health implications for marine organisms as it can trigger immune and reproductive issues and chromosomal damage. However, in a seminal study by Cao et al. (2018) on oysters, it was discovered that a combination of oxidative stress as a result of Ocean Acidification exposure and high Cadmium accumulation resulted in severe irreparable damage to oyster DNA. Therefore, this demonstrates how marine organisms are especially vulnerable to multiple environmental stressors and undergirds the urgency of managing anthropogenic activity.

 

References

Cao, R., Liu, Y., Wang, Q., Zhang, Q., Yang, D., Liu, H., Qu, Y. and Zhao, J., 2018. The impact of ocean acidification and cadmium on the immune responses of Pacific oyster, Crassostrea gigas. Fish & Shellfish Immunology, 81, pp.456-462.

Jin, P., Zhang, J., Wan, J., Overmans, S., Gao, G., Ye, M., Dai, X., Zhao, J., Xiao, M. and Xia, J., 2021. The Combined Effects of Ocean Acidification and Heavy Metals on Marine Organisms: A Meta-Analysis. Frontiers in Marine Science, 8.

Jussen, B., 2022. Coral Reefs Could Be the Next Major Casualty in the Fight against Climate Change. [online] The Climate Change Review. Available at: <https://www.ucsdclimatereview.org/post/coral-reefs-could-be-the-next-major-casualty-in-the-fight-against-climate-change> [Accessed 13 April 2022].

Mollica, N., Guo, W., Cohen, A., Huang, K., Foster, G., Donald, H. and Solow, A., 2018. Ocean acidification affects coral growth by reducing skeletal density. Proceedings of the National Academy of Sciences, 115(8), pp.1754-1759.

Shi, W., Zhao, X., Han, Y., Che, Z., Chai, X. and Liu, G., 2016. Ocean acidification increases cadmium accumulation in marine bivalves: a potential threat to seafood safety. Scientific Reports, 6(1).