Ocean acidification: The pH problem

Ocean acidification: The pH problem

Climate change is not the only major environmental problem humanity faces and needs to solve. The burning of fossil fuels and the ensuing release of carbon dioxide into the atmosphere and its absorption by oceans are directly affecting the marine life’s delicate and intricate ecosystems and thus, its survival. By interacting with, and interrupting the seawater’s natural chemical processes, the increase in underwater carbon dioxide is creating a much more acidic and unfavourable environment for all marine species.

Evidence that ocean acidification is happening has been detected throughout the world through several investigations. And all life, from the bottom to the top of the food chain— including humans— that are dependent on the ocean as a natural resource and for their survival, are at risk to the adverse effects of this acidifying process.

What is ocean acidification?

Ocean acidification is related to the increasing acidity at the ocean’s surface due to an increased uptake of carbon dioxide (CO2). Oceans are the planet’s biggest carbon sink, naturally absorbing CO2 that is released into the atmosphere. Studies suggest that between 1800 and 1994, 48% of all CO2 released by human activities was taken up by the oceans. When CO2 dissolves in seawater, a complex chemical reaction occurs which brings about a decrease in the ocean’s pH. pH is the scale that describes how acidic or basic a liquid is; representing how many hydrogen ions (H+) ions are present. The greater the concentration of H+, the lower the pH, and the more acidic a liquid is. Over the last 200 years, since the birth of the Industrial Revolution in the 18th century, our oceans’ pH has declined from 8.2 to 8.1. This 0.1 change may seem insignificant, but on the pH scale, it converts to an alarming 30% increase in acidity. Furthermore, if humans continue to emit CO2, ocean acidity may rise an additional 170% by the year 2100. Scientists use the term “acidification” to signify that the oceans’ pH is lowering, not that it is becoming acidic (having a pH below 7).

How ocean acidification works: chemistry explained

Carbon dioxide dissolves easily in water to form a weak carbonic acid (H2CO3).

CO2      +          H2O      ↔       H2CO3

A hydrogen ion (H+ ) is released in the reaction.

H2CO   ↔     H+        +          HCO3

The released hydrogen ions either remain as H+ and contribute to ocean acidification or they combine with carbonate (CO32- ) to form bicarbonate (HCO3).

H+        +          CO32-        ↔     HCO3

Under normal circumstances, calcium binds with carbonate (CO3) to form calcium carbonate (CaCO3). Calcium carbonate is used by calcifying species — crustaceans, corals, clams, mussels, echinoderms, oysters— to build hard, solid structures such shells or skeletons.

Ca2         +          CO32-    ↔    CaCO3

From the chemical equations above, free hydrogen ions readily combine with carbonate. Hence, the greater the increase in hydrogen ions, the less available carbonate ions there are to combine with calcium to synthesise calcium carbonate.

Effects of ocean acidification on marine life

Cold water absorbs more CO2 than warm water; thus, the polar regions’ diverse ecosystems are most susceptible to acidification. One investigation of pteropods (sea snails) collected from the Southern Ocean, revealed the sensitivity of shell-building organisms to changes in their habitat’s chemistry. The sea snails collected had severely damaged and weak outer shells, leading scientists to conclude that the lack of calcium carbonate building blocks inhibited the snail’s ability to build and repair their exoskeleton. Although the snails are tiny (size of a pea), they are an important food source for larger animals, and when their survival are threatened; so too is the entire food chain. Larvae oysters, from a commercial oyster seed hatchery in Oregon, have also been found to struggle to build their shell in an environment with a lower pH.

Acidification is also affecting reef-building corals. Research shows that acidification may threaten the early life phases of coral recruitment; jeopardising and reducing fertilisation and settlement of coral larval on the reef. Increased CO2 levels can also cause deformed and weak skeletons in juvenile coral recruits. Lastly, scientists discovered that changes in CO2 concentrations may severely affect learning abilities in juvenile fish. Experiments demonstrated that damsel fish, when exposed to CO2 concentrations estimated to be present by the end of the century, were unsuccessful in displaying an anti-predator response or detecting the predator’s odour.

Effects of ocean acidification on humans

As the process of ocean acidification advances, our planet’s oceans won’t become dangerous for humans to enter as the ocean’s pH will remain basic (having a pH above 7). However, since humanity is intrinsically connected to the oceans’ health, any minute changes or losses in marine ecosystems will affect us.

Firstly, since acidification interferes with the ability of shell-making organisms, such as mussels, shrimps, oysters, and mollusks, to build their calcium carbonate shell, there will be a decrease in the population numbers of these types of animals. Lacking a protective shell, these organisms become vulnerable and important life stages, such as larval settlement, reproduction, and survival to adulthood are critically threatened. Furthermore, larger fish rely on shellfish for food, so a diminished abundance of prey corresponds to a decline in fish populations. Finally, this loss in both shellfish and fish populations will affect millions of people around the world who rely on marine fisheries for food and their livelihood. Studies report that by the year 2100, approximately US$130 billion will be lost due to the reduction in the mollusk population. Lacking alternative protein sources and agricultural opportunities, especially within island communities, will cause drastic ramifications on social and economic sectors on a global scale.

Secondly, many coastal communities and marine ecosystems rely heavily on coral reefs for their survival. Coral reefs are home to an incredibly diverse variety of species— research reveals that more marine life has evolved in coral reefs compared to any other marine ecosystem. Reefs provide shelter and food to an abundance of species and is an important oasis for the reproduction and maturity of many organisms. Healthy coral reefs act as a natural barrier that protects coasts from erosion, storms, floods, and massive waves. Losing this critical protection, valued at US$9 billion a year, places many lives at risk— especially since climate change is creating unpredictable weather patterns— and threatens coastal infrastructure, such as hotels and resorts.

Losing this indispensable habitat will not only affect the complex food web and intricate energy balance, but also the billion dollar tourist industry that depends on coral reefs for recreational and commercial purposes. For example, the entire scuba diving industry has the potential to collapse; creating a disastrous domino effect on all sectors involved in this sport. Companies who produce dive equipment will lose revenue; dive centres will close down, and people will lose their jobs.

What can be done?

Ocean acidification is a global environmental problem with severe repercussions for both marine ecosystems and the lives of millions of people. Governments worldwide need to, therefore, commit to reducing their CO2 emissions in half by 2050, as well as move towards making renewable energy, such as wind and solar, the primary source of energy. Moreover, as our oceans are invaluable, ecosystems already under threat must be protected by law and environmental policies. Sustainable fishing techniques need to be implemented and controlled to protect the ocean’s biodiversity and avoid species extinction. By working together and by empowering communities with knowledge, we can prevent ocean acidification destroying one of our most important natural resources.

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