What Is Ocean Acidification?

By Aarushi Gurnani

https://coastadapt.com.au/ocean-acidification-and-its-effects#:~:text=Ocean%20acidification%20reduces%20the%20amount,shells%20may%20begin%20to%20dissolve.

Ocean acidification or OA is the process of ongoing decrease in the pH of the Earth’s oceans, caused by the uptake of carbon dioxide from the atmosphere. While the OA process tends to occur naturally over geologic timescales, currently, the oceans are acidifying at a faster rate than what the planet has ever experienced before. The unprecedented rate of ocean acidification is expected to have devastating consequences on marine life, particularly shellfish and coral reefs. Current efforts to combat ocean acidification are largely focused on slowing the pace of ocean acidification and bolstering the ecosystems capable of dampening ocean acidification’s full effects.

What Causes Ocean Acidification?

The primary cause of ocean acidification, today, is the ongoing release of carbon dioxide into our atmosphere from the burning of fossil fuels. This released carbon dioxide is then dissolved into the ocean and leads to a lowering of the water’s pH, making the ocean more acidic.

Additional culprits include coastal pollution and deep-sea methane seeps (a process by which methane gas escapes from the rock into the ocean above it). The reason for increase in acidic content of the ocean can be traced back to the the start of the industrial revolution about 200 years ago, when human activities began releasing large amounts of carbon dioxide into Earth’s atmosphere, making the ocean’s surface 30% more acidic.

Once dissolved in seawater, carbon dioxide goes through a series of chemical changes. Dissolved carbon dioxide first combines with water to form carbonic acid. From there, carbonic acid can break apart to generate standalone hydrogen ions. These excess hydrogen ions attach to carbonate ions to form bicarbonate. Eventually, not enough carbonate ions remain to attach to each hydrogen ion that arrives in seawater via dissolved carbon dioxide. Instead, the standalone hydrogen ions accumulate and lower the pH, or increase the acidify, of the surrounding seawater.

On the other hand, In conditions which are non acidifying, much of the ocean’s carbonate ions are free to make connections with other ions in the ocean, for example with calcium ions to formulate calcium carbonate. These carbonate ions can also be used by animals that need these ions to form their calcium carbonate structures, like coral reefs and shell-building animals. Thus, these Shell-building organisms can’t extract the carbonate ions they need from bicarbonate, preventing them from using that carbonate to grow new shells. In this way, the hydrogen essentially binds up the carbonate ions, making it harder for shelled animals to build their homes.

The Impact of Ocean Acidification

Impact on marine life

As mentioned above, Ocean acidification reduces the amount of carbonate content in the ocean which is a key building block in seawater. Thus, making it more difficult for marine organisms, such as coral and some plankton, to form their shells and skeletons, and existing shells may begin to dissolve. The figure below shows A mollusc shell slowly dissolving under acidic conditions. The shell almost completely dissolves after 45 days when placed in seawater with pH and carbonate levels projected by models for the year 2100.

David Liittschwager/National Geographic Creative.

While some ocean animals such as certain types of mollusks have the ability to hold on to their shells in the face of an acidifying ocean. For instance, clam-like animals known as brachiopods have been shown to compensate for the ocean’s dissolving effect by creating thicker shells. Other shell-building animals, like the common periwinkle and the blue mussel, can adjust the type of calcium carbonate they use to form their shells to prefer a less soluble, more rigid form. However, this case is not so common and for many marine animals that cannot compensate, ocean acidification is expected to lead to thinner, weaker shells. Moreover, even these fighting tendencies come at a greater cost, in order to grasp on to a limited supply of calcium carbonate building blocks, these animals must dedicate more energy to shell-building to survive. As more energy is used for defense, less remains for these animals to perform other essential tasks, like eating and reproducing.

Impact on human societies

Changes in marine ecosystems will ultimately also result in dire consequences for human societies, which depend on the goods and services provided by these ecosystems. This could be seen in substantial revenue declines, loss of employment and livelihoods, and other indirect economic costs. Socioeconomic impacts associated with the decline of the following ecosystem services are as follows :

1. It can have a negative effect on the food web in the ocean. Since OA makes it difficult for crabs, oysters and urchins to build the shells they need to survive. Some hatcheries have lost 80% of their oyster production. When the small animals die off, there’s less food for larger fish and marine mammals. And this further will affect the food secutiry of the human world as well.
2. Marine ecosystems such as coral reefs protect shorelines from the destructive action of storms and cyclones. Without this protective function of reefs there can be loss of life, property damage, and erosion.
3. The capacity of the ocean to absorb CO2 decreases as ocean acidification increases. More acidic oceans become the less they are able to participate in moderating climate change.

What Can Be Done?

The ultimate solution in dealing with ocean acidification is reducing — or even reversing — carbon dioxide emissions remains the best way to limit ocean acidification.

Meanwhile, certain steps have been recommended by the CoastAdapt website which I have listed down below :

1. Improving water quality : This entails monitoring and regulation of localised sources of acidification from runoff and pollutants such as fertilisers.
2. Adopting of sustainable practices for fisheries management : Regulating catches to reduce overfishing and creating long-term bycatch reduction plans.
3. Implementation of new technologies: Adopting diverse techniques on the basis of industry. For example, in the aquaculture industry, new forecasting systems have been developed to account for seasonal upwellings that bring low pH seawaters to the ocean surface and cause massive shellfish die-offs.
4. Sustainable management of habitats: Increasing coastal protection, reducing sediment loading and applying marine spatial planning.
5. Establishment and maintenance of Marine Protected Areas: Protecting highly vulnerable and endangered marine ecosystems.