The Effects of Ocean Acididfication
What is Ocean Acidification?
Since the industrial revolution, carbon dioxide emissions have rapidly increased due to deforestation and the burning of fossil fuels. Oceans have absorbed about a third of the carbon dioxide (CO2) produced from human emissions since the 1800s. Half of this is accounted for by the burning of fossil fuels (“How Does Climate Change Affect Coral Reefs”). Much of today’s news focuses on other environmental issues, such as global warming, but there continues to be little focus on this issue. Many are not aware of the problem at hand. A study conducted by National Geographic reported that our oceans are absorbing roughly 22 million tons a day. If emissions continue, predictions show that the current pH of around 8.1 will be reduced by another 0.5 units by the end the century ("Ocean Acidification”). When carbon dioxide is released into the environment and dissolves in the water, the ocean’s pH is significantly lowered over time. “Over the past 300 million years, ocean pH has been slightly basic, averaging about 8.2. Today, it is around 8.1, a drop of 0.1 pH units,
representing a 25-percent increase in acidity over the
past two centuries” (“Ocean Acidification”). This decrease in pH causes reproductive disorders and a restrain in the shell growth of corals. Another
recent study showed a decrease in coral growth in the Great Barrier Reef of Australia of 14% since 1990. This is the most significant decrease in growth within the past 400 years ("Effects of Ocean Acidification on Corals”).
How Does Ocean Acidification Happen?
As carbon dioxide emissions rise amongst the world, the pH level shows a correlating decline. This happens as carbon dioxide from the
atmosphere dissolve in water
to form carbonic acid. Carbonic
acid then rapidly breaks down
into hydrogen ions and bicarbonate ions. The bicarbonate ions eventually
entirely break down into carbonate ions and more hydrogen ions. The chemical equation, further explained in the illustration below, is as
follows: CO2 + H2O ⇆ H2CO3 ⇆ HCO3- + H+ ⇆ CO32- + 2H+. As H+ increases, the reaction shifts left, causing a decrease in the amount of available carbonate ions. Because of saltwater’s natural ability to buffer against changes in the pH, which has the net equation of CO2(aq) + CO32- + H2O → 2HCO3- , the increase in acidification is not as evident. However, with the constant addition of carbon dioxide in our environment, saltwater’s buffering capacity will decrease. An increase in acidity acts similar to osteoporosis in many species of corals and shellfish. As the pH decreases, corals’ skeletons become
extremely brittle and weak. This is caused by coral’s growth Process of CO2 dissolving in water (“What is Ocean Acidification”). This process including the depositing of calcium carbonate as part of their skeletons. When CO32- concentrations decrease, a shift in the reaction due to Le Chatelier’s principle, the calcium carbonate skeletons will start to dissolve, as there is less of the calcium component. Due to this, corals need to exude more energy in order to grow skeletons and reproduce new genetically identical colonies. Research has shown that a lower pH can also contribute to a declination in fertilization, development of larvae, and settlement, the point at which the coral larvae attempt to attach themselves to solid matter in order to start producing colonies. “And if any of those steps doesn't work, you're not going to get replacement corals coming into your system,” ("Ocean Acidification”). The entirety of the acidification of the ocean that has occurred so far is most likely irreversible. If the human emissions of carbon dioxide halted, thousands of years would go by before the ocean turned back to the way it was before the industrial revolution, at a pH of 8.2. National Geographic states that a drop in pH by 0.1 is equivalent to a 30% increase in the water’s acidity. If this rate continues, the pH will be expected to drop to around 7.8 by 2100. In comparison to 1800, the ocean will be up to 150% more acidic (“Ocean Acidification”). Another factor to consider in ocean acidification is known as bioerosion. Bioerosion is the process where reef dwellers utilize sections of the coral’s skeleton for food or shelter. Corals must grow faster than the rate at which they are eroded. However, due to the high levels of carbon dioxide, coral growth is slower, and coral skeletons are weaker. This being said, coral reefs exposed to acidification may not be able to compensate for bioerosion, and will start to shrink (“Effects of Ocean Acidification on Corals”).
What else is affected by Ocean Acidification?
Other organisms as well as corals are negatively affected by an increase in oceans’ pH. Acidification could eventually lead to a decrease in diversity of sea animals and will affect the sustainability of marine life on Earth. Many organisms depend on coral reefs for food and shelter, as noted by Oceana in “Effects of Ocean Acidification on Corals". “Millions of marine species depend on coral reefs to feed, reproduce, shelter larvae and take refuge from predators in their vast three dimensional networks. If coral reefs disappear, it will threaten the survival of many reef dependent species.” Almost 25% of all species in the ocean expend a portion of their life in coral reefs ("Ocean Acidification"). Besides corals, ocean acidification also negatively affects other organisms that are required to make shells using calcium carbonate in order to survive including snails, clams, and urchins. Coral’s decreased calcification ability due to a decrease in the pH directly affects their role in the ecosystem, altering not only the organisms but the entire ecosystem itself.
What is going to happen in the future?
Predictions on the calcifying rates of corals decrease as acidification continues to turn the oceans more acidic. Corals and additional calcifying species are expected to calcify 10–50% less than pre-industrial rates by the middle of this century (Kleypas and Yates). Many researchers believe the coral reef species will die out entirely eventually. “According to Dr. Ken Caldeira, ‘There is at least a reasonable expectation that if current carbon dioxide emission trends continue, corals will not survive this century’”("Effects of Ocean Acidification on Corals”). Corals are the foundation of the oceanic ecosystem, and it is evident that if corals die, the whole ecosystem will experience negative effects.
Are there any solutions to Ocean Acidification?
One possible solution entails increasing the diet of corals by exposing the coral to an excess of brine shrimp (plankton), which, when tested, resulted in the reduction of the effects seen brought on by acidification. This mechanism increases coral’s calcification ability by allowing the coral to consume more food, causing the addition of tissue. Scientists predict that the excess in plankton causes the coral to grow larger and change its structure, increasing its ability to construct calcium carbonate skeleton even in the current conditions (“Trouble in Paradise: Ocean Acidification”). Besides plankton, another solution in consideration includes the use of oysters in bodies of water. Oyster shells store calcium carbonate, a weak conjugate base, which is released when the shell is dissolved. This increase in the carbonate concentration allows the previous reaction of HCO3- ⇆ CO32- + H+ to shift left and counteract the acidic pH caused by carbon dioxide. Oysters have proven to regulate the pH of several bodies of water including the Chesapeake Bay. However, the oyster population is significantly decreasing which poses an extensive problem for this solution. Furthermore, some say that this small solution won’t be enough to show an impact on the larger levels of ocean acidification. Although the effect of this will mostly be localized, numerous researchers concur that while oysters may not be able to fix ocean acidification on a global scale, many benefits of the shells do exist. With limited solutions, it is necessary to educate others about the negative impact ocean acidification can have on not only marine species, but a large segment of the economy. By raising awareness about this issue, it is possible to influence the creation of worldwide policies limiting the burning of fossil fuels. Optimistic speculations predict a positive turn in the environment if these greenhouse gas limitations are initiated. If simple changes are enforced within the home, the collective contrast to today’s conditions will expose a brighter future of our oceans.
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Corals in the waters of Tatawa Besar, Komodo islands, Indonesia taken at different times (Robert and Ishak).
By: Haley Greenspan
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