Journal of Geophysical Research. Vol. 110. (2005).
Ken Caldeira, working at the Carnegie Institution, performed a study on ocean acidification that predicts the pH and aragonite saturation of the ocean in 2100 based on several different atmospheric carbon dioxide prediction models. He predicts aragonite will be undersaturated in the Southern Ocean by 2100. The model that predicts this happens to be one of the most conservative projections also. This leaves many to question whether ocean organisms will be able to sustain shell calcification past this date. This models predicting future pH measurements of the ocean are useful for other researchers. It gives them a good pH range to expose organisms to. The way they respond in the these environments will enable scientists to better understand organism specific responses to ocean acidification. The study also argues against the use of deep-sea carbon dioxide injection. Caldeira states that this will solve approximately ten percent of the problem but does not offer a better solution.
Is the response of coral calcification to seawater acidification related to nutrient loading?
Coral Reefs 30 (2011) 911–923
Ocean acidification, or the increasing concentration of CO2 in ocean water, has been shown to have a negative effect on coral calcification. Increasing CO2 lowers aragonite saturation state (Ω). Generally, Ω decreases linearly with calcification; however, in some cases, it has little or no effect on calcification. Can higher nutrient content be mitigating the negative effects of low Ω?
A study by Chauvin, Denis, and Cuet shows that nutrients do, in fact, play a role in promoting coral calcification in low Ω environments. Their experiment found that a modest nitrate addition increased calcification. Nitrates play a role in photosynthesis, and consequently promoted photosynthesis could be the factor directly stimulating calcification. These nutrient-enriched coral showed no relationship between calcification and Ω, suggesting that an excess nutrient environment compensates for low values of Ω. This evidence can be used to explain why some coral reef environments thrive even under low Ω conditions.
Nature, 437, 681-686 (29 September 2005)
In a study done by Orr et al., the decreasing rate of free carbonate ion available for calcification for sea organisms will become undersaturated by 2050. Calcium ions in the ocean react with carbonate ions to form calcium carbonate which makes up exoskeletons of various sea organisms. The excess of dissolved carbon dioxide in the ocean has caused increasing amounts of carbonate to become tied up in bicarbonate ions which are unable to be used to form calcium carbonate. Pteropods have shown significant decreased calcification in water the same pH predicted with the “business-as-usual” projections. They are near the bottom on the food chain, and a change in their population could have a ripple effect throughout the entire ocean ecosystem. In higher altitude ocean ecosystems, this study has shown that acidification is increasing at a slower rate. This only means that these ecosystems will lag the lower altitude ones by 50-100 years. The only benefit to this is that these organisms have more time to possibly adapt to the new ocean chemistry.
Annual Review of Marine Science. Vol. 1: 169-192 (January 2009)
A study by Doctors Doney, Fabry, Feely, and Kleypas on increased emissions of anthropogenic carbon dioxide into the atmosphere shows the ocean acts as a sink for carbon dioxide and takes in one third of all carbon dioxide in the atmosphere. Dissolved carbon dioxide reacts with water to form carbonic acid. This has lead to a steady decrease in the pH of the ocean. Simply having more acidic ocean water is not the only issue that arises from the dissolved carbon dioxide. There are less free carbonate ions in the ocean water that are able to react with calcium ions in order to form calcium carbonate which is a key component of exoskeletons and shells in sea organisms. This is leading to the erosion of coral reefs and decreased ability of various plankton to form strong exoskeletons. Plankton are low on the food chain, and if they were to struggle, it could have negative effects on the whole ocean ecosystem.
Science DOI: 10.1126/science.1155676
The study by Richard A. Feely of the National Oceanic and Atmospheric Administration, and others, shows that the coastal waters of western North America are being noticeably affected by ocean acidification.
The study performed looked at how naturally occurring upwelling affected the aragonite saturation and pH level of the coastal waters. Usually undersaturated water is found in the depths of the ocean, but the study discovered that with upwelling, some regions of the continental shelf had undersaturated waters all the way to the surface. These saturation levels have risen 50 to 100 meters since preindustrial times.
What this all means is that as the saturation horizon continues to rise, there will be less and less water that is not corrosive to calcifying organisms. With these organisms at the base of the food chain, we could see a very large chain reaction that affects the ocean’s inhabitants right off our shores.
Global Change Biology (2011) 17, 3254–3262, doi: 10.1111/j.1365-2486.2011.02473.x
Much research has been done to show that calcifiers are affected by ocean acidification; however, only few explain the specific effects that ocean acidification has on specific calcifiers. With this said, some calcifying organisms may be more or less affected by ocean acidification than others. The study by Catriona L. Hurd, at University of Otego in Dunedin, New Zealand, and his colleagues suggest that calcifiers have fundamentally different species-specific traits that must be considered when looking at the influence that ocean acidification has on the species. For instance, the site of calcification may differ according to the organism. In further explanation, some species, like abalone, may calcify internally. Hurd’s results predict that the calcification of such a species may not be directly effected by a reduced pH. Another species-specific characteristic is that of the outer surface of calcifying gastropods and bivalves is covered by a ‘protective’ organic layer. Hurd’s results show that this characteristic can also determine how ocean acidification may affect the species. Hurd concludes that predicting species-specific responses and subsequent ecosystem restructuring to ocean acidification is complex and requires a holistic, eco-mechanical, approach.
When environmental problems having to do with the absorption of CO2 are mentioned, global warming immediately comes to mind. This may be due to the fact that people think it is the only environmental issue concerning CO2 that is relevant. What most are not aware of is that almost a quarter of all the anthropogenic carbon dioxide in the atmosphere is being absorbed into the oceans. This absorption of carbon dioxide into the oceans causes several changes in ocean chemistry including increases in CO2 concentration, decreases in pH, and decreases in calcium carbonate saturation. Naturally, the group most affected by all these changes, are the marine organisms, whose biological processes (respiration, CO2 fixation, uptake of growth nutrients, etc) are being negatively altered.
One such processes that is being affected, and not positively so, is the precipitation of calcium carbonate. When gradual seawater acidification is caused due to the absorption of fossil fuel carbon dioxide, calcification has been shown to slow down in come of the predominant calcifying groups (corals, cocolithopores, and foraminifera.) This is because when carbon dioxide is absorbed into the oceans, the water becomes more acidic, and thus its degree of saturation is reduced in regards to calcium carbonate (CaCO3.) Why is CaCO3 so important to marine organisms? It is the major constituent of many marine organisms’ protective shells, plates, and skeletons. In addition, the calcifying organisms include several different taxonomic groups and inhabit various ecological niches. Of those calcifying marine organisms that have been studied so far, most display either a slower rate of calcification or a decrease in total mass of CaCO3 per organism in response to the increase in CO2 levels and lower pH values in the sea water. In fact out of all observed biological effects of the acidification of ocean water, the most widely-observed and best known effect is the decrease in calcification/shell weight.
However, not all results pertaining to calcification due to ocean acidification are agreeable with this observation. A 60 d laboratory experiment done by Ries et. al. in 2009 investigated the effects of carbon dioxide induced ocean acidification on calcification in 18 benthic marine organisms from a broad range of taxa (crustacean, cnidarian, echinoidea, rhodophyta, cholorophyta, gastropoda, bivalvia, annelida. While in ten out of the eighteen species, reduced rates of net calcification were observed, in seven of the eighteen species, net calcification actually increased under the intermediate and even highest levels of carbon dioxide! The remaining species showed no change in net calcification. In another experiment by Langer et. al. in 2006, it was shown that that two of the most productive marine calcifying species (the coccolithophores Coccolithus pelagicus and Calcidiscus leptoporus) also did not follow the expected calcification results in response to ocean acidification. Thus, these diverse and varied results in response to ocean acidification demonstrate the differences between organisms when it comes to regulating pH at the site of calcification. Thus, even though there may be an overall trend in calcification in marine organisms as a result of increased CO2 levels in ocean water, the results are in fact quite varied.
Ries, J.B., A.L. Cogen, and D.C. McCorkle. 2009. Marine calcifiers exhibit mixed responses to CO2 induced ocean acidification. Geology 37(12): 1131-1134.
Langer G. et.al. 2006. Species-specific responses of calcifying algae to changing seawater carbonate chemistry. Geochemistry Geophysics Geosystems 7: Q09006.
Coral reefs constitute a very important component of many ecosystems across the world’s oceans. Although such reefs occupy less than one tenth of a percent of the oceans’ surface, these diverse ecosystems house twenty-five percent of the world’s marine organisms. The rigid structures that compose coral reefs are formed by a process known as calcification performed by polyps, small marine organisms, which then die and leave behind their calcified shells. However, with increasing carbon dioxide levels in the ocean, calcification can be negatively affected, thereby harming the whole of the world’s coral reef ecosystems.
Under normal conditions, the process of calcification begins with the combination of carbon dioxide and water to form carbonic acid. The carbonic acid subsequently dissociates into a hydrogen ion and a bicarbonate ion, which then breaks down into another hydrogen ion and a carbonate ion. Finally, calcium combines with the carbonate to form a hard calcium carbonate shell. However, when extra carbon dioxide comes into the process, the process shifts so that fewer quantities of calcium carbonate form, causing weaker, smaller calcium carbonate complexes to form reefs. These smaller, weaker reefs inherently cannot house as many organisms as their larger counterparts, and as the oceans continue to acidify, the reefs will continue to wane smaller and weaker. Ocean acidification also slows the growth of reefs, makes coral more susceptible to bleaching and disease, reduces the tolerance of reefs to ultraviolet radiation, and accelerates bioerosion; the combination of such negative effects on reef formation could lead to an eventual disappearance of the structures from the world’s oceans.
Multiple laboratory studies have shown substantial declines in reef growth associated with ocean acidification. In such studies, a doubling of the amount of atmospheric carbon dioxide has led to a decline of three to sixty percent in the rate of calcification. Likewise, calcification rates of brain corals in Bermuda have decreased by twenty-five percent during the last fifty years due in part to increasingly acidic ocean waters. In another study by the United States Geological survey, crustose coralline algae, another important part of reef building, also becomes much less effective in more acidic waters. In water tanks with decreased pH, crustose coralline algae covered ninety-two percent less area than in the tanks with normal ocean water. In addition, non-calcifying algae increased in area by fifty-two percent, showing its ability to outcompete the important crustose coralline algae in acidified ocean environments. A study at the University of Hawaii showed that dominance in reef building could shift from stony corals to fleshy algae in acidified oceans. This shift would lead to not only changes in the reefs themselves but also in neighboring coastlines, thereby drastically changing the ecosystems of the area.
Ocean acidification has many negative effects on coral and other crucial components of the calcification and the reef building process. Such adverse effects could lead to the eventual disappearance of reefs from the ocean, greatly impacting the lives of many marine organisms inhabiting reef-based ecosystems. Changes in reefs also cause changes in nearby coastlines, which will disturb the living conditions of even more organisms. If ocean acidification continues, the effects on coral reefs will snowball and disrupts a sizeable portion of the world’s marine organisms.
Ocean absorption of CO2 has helped alleviate some of the potential effects of increasing atmospheric CO2 levels, but in doing so has changed the chemistry of the seawater. The chemical reaction from CO2 absorption decreases the water’s pH levels, making the water more acidic. Since the Industrial Revolution, the pH has dropped .1 units and is expected to drop another .3 units if CO2 emissions continue the way they are now. It is uncertain how marine organisms are going to adapt to increased acidity, making the potential threat of ocean acidification alarming. One of the main processes seriously affected by the change is calcification, which enables organisms to produce their shells or skeletons. Increased levels of CO2 in the ocean will shift the carbonate system equilibrium towards higher concentrations of CO2 and lower carbonate ion concentrations. Carbonate ions are essential in order to produce calcium carbonate, which is needed to develop the shells of oysters and mussels.
The change in pH, affecting coral reefs and other calcifying organism, particularly imperils oysters and mussels. Studies have shown that the calcification rates of the edible mussel and Pacific oyster are strongly correlated with increasing concentrations of CO2.If the pH levels continue to decrease as projected, the ability of these mussels and oysters to produce shell material will decrease by 25% and 10% respectively by the year 2100. Oysters are less sensitive to increased levels of CO2, due to their differing shell composition. Mussel shells are composed of mostly calcite, while oyster shells contain a large amount of aragonite. Currently, calcium carbonate is readily available to these organisms so that they can create their shells, but soon it will become harder, requiring greater expenditures of energy, for these organisms to produce shells.
Mussels and oysters are an integral part of the fishing economy and the predicted decrease in calcification due to ocean acidification will lead to significant economic losses. Global shellfish production has had an annual increase of 7.9% over the last 30 years, which corresponds to a commercial value of 10.5 billion US dollars. The Pacific oyster was the most cultivated species in 2002 and represented 10.8% of the total world aquaculture production, while mussels represented 3.6% of total production. There are fishermen whose livelihoods depend on the sale of shellfish. Although a much more sudden example, many fishermen were put out of work and incapable of providing for their families after the oil spill in the Gulf of Mexico. A similar thing could happen if ocean acidification continues to make calcification increasingly difficult. Any decline in these species will cause considerable damage to the fishing market as well as have major consequences for coastal biodiversity.
Mussels and oysters serve an important purpose in coastal ecosystems. They both regulate energy and nutrient flow, as well as provide habitats for other species. If the population of mussels and oysters diminishes because of their inability to calcify and make shells, there will be huge repercussions for biodiversity and the function of the ecosystem.
The ocean has absorbed carbon dioxide (CO2) from the atmosphere since the beginning of time. The ocean is known as a carbon dioxide sink because of its absorption capabilities. This has been viewed as a positive in the past few decades since global warming has become a pressing issue. The ocean absorbs CO2 from the atmosphere, which helps lessen the threat of global warming to the earth. Carbon dioxide levels have risen since the Industrial Revolution due to automobile emissions, cement production, industrial power plants and other contributing factors. Now, with the oceans absorbing absorbing about 1/3 of the earth’s carbon dioxide, the sea chemistry is being affected. The ocean cannot handle such high levels of CO2 as a result, its pH is becoming more acidic. This effect is known as ocean acidification.
Before the Industrial Revolution, the ocean’s pH levels were stable. Since then, the pH has dropped 0.1 units. Though this may seem like a relatively small change, the world’s ocean has a very high buffering, or acid neutralizing, ability so the fact that the pH has declined to this extent is very startling. PH levels are predicted to drop even more in the next century.
Like all ecosystems, marine ecosystems are comprised of a vast array of interactions between different species and different types of organisms (both alive and dead) and the physical environment. Therefore, a change in any of these aspects will lead to a plethora of changes throughout the rest of the ecosystem. Because of the sheer quantity of life present and the significant interactions between species, coral reefs are prime candidates to be affected greatly by ocean acidification. These reefs provide food and shelter to hundreds of thousands of marine organisms so when the reef is harmed by acidification, so are all of the organisms that interact with it. When global warming, one of the world’s most alarming environmental threats directly affects the coral reef, one of the ocean’s most important ecosystems, the ramifications are dire.
Coral reefs are created by large calcium carbonate colonies known as coral. These reef structures are the home and feeding grounds to a wide array of organisms. Coral reef ecosystems have been called “cradles of evolution” because more marine organisms evolve from coral reefs than from any other ecosystem.
Ocean acidification may actually alter the physical structure of coral reefs. Acidification affects the organisms that build the reef because it lowers calcification rates and pH, inhibiting the creature’s skeletal growth. Without these reef-building organisms, coral reefs cannot exist.
Aside from hindering the organisms that physically build the reefs, ocean acidification also increases the probability that existing reef structures may dissolve. Reef erosion is likely, given the vulnerability inevitable with increased acidification.
Acidification raises the possibility of coral mortality. It can cause coral bleaching, which can cause the coral to die. As the coral tries to survive and is in a weakened state, they become vulnerable to encroachment by other marine organisms. Some species can benefit from higher water acidity, like macroalgae. As these algae thrive, they block sunlight from getting to the coral and they may be abrasive to coral structures as they move through the water in the current. Both low light and abrasive contact can weaken the coral, or even kill the reef structure.
Dissolving and eroding coral reefs, as well as coral that is lost because of displacement by other organisms that can survive better in the high acidity all lead to what is known as “reef flattening”. This is a phenomenon that creates a loss in the “architectural complexity” of the reef. This affects all of the organisms that live within and rely on the reef as a key part of their survival methods. Reef flattening diminishes reef structure and habitats, and reduces organism populations and biodiversity.
Coral reefs are home to over 25% of all known species of fish and exhibit the highest biodiversity of any ecosystem in the entire ocean. Threats to coral reefs are a threat to thousands of other organisms, so as we see ocean acidification harming our world’s coral reefs, we should be very concerned. Ocean acidification does not mean that the oceans will die, but the survivors may be algae and jellyfish. For the ocean to be sustainable in its present form, with coral reefs the prominent sanctuaries for marine life, the pH of the ocean has to maintain acidity within relatively narrow boundaries. With the alarming increase in CO2 being absorbed into our great carbon dioxide sink known as the ocean, the coral reef is in jeopardy.
“Chapter 4.” Ocean Acidification: a National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. Print.
Eilperin, Juliet. “Growing Acidity of Oceans May Kill Corals.” The Washington Post: National, World & D.C. Area News and Headlines – The Washington Post. 5 July 2006. Web. 04 Sept. 2011. <http://www.washingtonpost.com/wp-dyn/content/article/2006/07/04/AR2006070400772.html>