Research has shown that the acidification of the ocean—the lowering pH level of ocean water on earth—may affect ocean life in multiple ways. One effect of note is the adverse effect a more acidic environment can have on nutrient availability. Nutrients are necessary for all life, and the ocean may soon not provide enough. Ocean acidification can do one of three things when it comes to this issue. First, it can change the chemical forms of vital nutrients. Second, it can stymie the conversion of the nutrients into usable forms. And third, it can actually change the nutrient requirements of the plant or animal (p. 54).

In the first case, metals like zinc, cobalt, nickel, and iron may become less available due ot chemical changes. These metals are important to all organisms (humans consider them vitamins). They need to be absorbed by the cells inside organisms, a process that is very easy when the metals are free ions (not bound to another element) or bound to an inorganic molecule. Unfortunately, a decrease in pH increases the tendency for such molecules to join organic complexes and increases the difficulty associated with absorbing these vital metals (p.54). Luckily, there is hope. An increase in acidity (decrease in pH) has also been shown to cause in increase in the solubility of iron oxide, a process that would increase the availability of free iron in the water.

The phytoplankton, a member of the plankton family that carries out photosynthesis, is the central organism in the second case (Source 1). These phytoplankton have the ability to cleave phosphate from organic compounds so it can be used by other organisms. The process requires the use of the enzyme alkaline phosphatase. Enzymes are proteins that significantly speed up chemical and biochemical reactions. Although they are very useful in carrying out most reactions, they only function in a specific pH range (Source 2). Unfortunately, alkaline phosphatase is beginning to die out because the pH of the Ocean is beginning to drop below the necessary pH range for its function. AP (alkaline phosphatase) functions very well at a pH around 9.0 (according to the chart on p. 55), but drops sharply after that. This means the drop in ocean pH from 8.2 to 8.1 could be a very serious difference. In fact, around 7.5, AP will stop functioning completely (p. 55). Without alkaline phosphatase, not only will phytoplankton find it harder to survive, but also other organisms will not be able to reap the benefits of free phosphate that the phytoplankton provide.

The third case is also strongly linked to the activity of phytoplankton. Research has shown that high levels of CO₂, the element responsible for ocean acidification, can alter the biochemical processes inside phytoplankton. Phytoplankton output both carbon and nitrogen under normal conditions, but under acidified conditions, they produce a much higher Carbon to Nitrogen ratio than normal (p.55). This means phytoplankton can change their carbon and nitrogen requirements. This does not bode well for other organisms. The more carbon there is in the ocean, the more likely it is that other free elements will bond with carbon creating an organic compound from which it is too difficult to absorb nutrients.

Overall, unless something is done about ocean acidification, it is possible that the increasing acidity will make it very difficult for ocean life forms to absorb the nutrients necessary for survival.

1: http://earthobservatory.nasa.gov/Features/Phytoplankton/

2: http://science.howstuffworks.com/environmental/life/cellular-microscopic/cell2.htm

Contrary to the many examples of decreased, depleted, and abnormal growth presented in “Ocean Acidification,” Photosynthetic organisms such as phytoplanton use carbon dioxide and sunlight energy to form organic matter.  Carbon Dioxide near the surface of the oceans are in low concentration; therefore, carbon fixation must occur to increase the concentration to a level which  can be used by the photoplankton. Carbon fixation is a arduous and energy-consuming process because carbon dioxide feasibly diffuses  through photosynthetic organisms’ membranes and cells; an increase in carbon dioxide concentration would augment marine photosynthesis and lead to an increase in primary production. An increase could be seen at first beneficial toward the production of organic matter; however, they are many significant direct and indirect effects that must be considered before propagating a conclusion.

There have been many experiments conducted that illustrated an increase of productivity in specific phyotoplankton species with increased levels of carbon dioxide.  Coccolithohpores for example, have increased the productivity of photosynthesis and have shows an increase in their calcification process. (http://www.bbc.co.uk/dna/h2g2/A3709433)

Many scientist have concluded that global warming is an effect from increased levels of carbon dioxide in the earths’ atmosphere; many scientists have interpreted the increase in the earth’s temperature as an extreme negative influence on organism of many ecosystems and the bane of biodiversity. However, recent studies of the history of oceanic plankton, such as diatoms,  exhibit a declination of the species in accordance to global cooling.  Studies from Cornell University therefore gives influential information that global warming due to carbon dioxide does in fact have positive effects towards oceanic organisms. (http://www.sciencedaily.com/releases/2009/01/090108111419.htm)

Although there is a plethora of evidence that increased levels of carbon dioxide is beneficial toward the growth of phytoplankton and production of organic matter, increased concentration of carbon dioxides has other direct and indirect effects that actually illustrates the contrary. Evidence shows that increased levels of carbon dioxide leads to ocean acidification, the process of acidifying ocean waters. Ocean acidification can alter the chemistry of key oceanic nutrients such as iron, nitrogen, and phosphorus. Additionally ocean acidification effect he biochemistry of oceanic plankton and photosynthetic organisms by changing the activity of their enzymes. While increased levels of carbon dioxide may increase production of organic matter, ocean acidification obstructs the same process by limiting nutrients in the ocean. Oceanic organism who rely heavily on metals such as zinc, iron, copper and cobalt will have a more difficult time acquiring these nutrients due to acidified water. This will in turn hinder the growth of these organisms.

There is no doubt that there exist evidence that gives insightful information from both sides. I believe the differences of the arguments come from the different perspectives that the scientists are attacking. For instance, scientist who show evidence that increased levels of carbon dioxide is beneficial for phytoplankton growth are only looking at the phytoplankton themselves. While scientist who argue on the negative effects of ocean acidifications look at the system of possibilities of indirect effects. While both sides present meaningful evidence. It is very difficult to come to an conclusion because the differences create an endless loop.

“3.4.” Ocean Acidification: a National Strategy to Meet the Challenges of a Changing Ocean. Washington, D.C.: National Academies, 2010. 54. Print.

The Effects of Ocean Acidification on Pteropods

While there is a wide range of negative effects expected in the future due to ocean acidification, there are some cases that have much more potential fallout than others. One of these cases is plankton. Plankton plays a crucial role in food webs, and therefore any damage done to plankton species will have a ripple effect that spreads throughout the ecosystem. A prime example of plankton that is at risk due to ocean acidification is the pteropod. While much uncertainty remains regarding the severity of future damage to pteropods, the prospect of a losing a key part of the food web is frightening. The ocean’s changing chemistry will inhibit pteropods’ ability to grow and survive, subsequently creating imbalance (decreasing biodiversity) among the various plankton species and creating problems further up the food chain.

Pteropods are snail-like plankton that float through ocean waters consuming smaller plankton. They, like many other marine organisms, rely on the process of calcification to grow their shells (which consist of aragonite and calcium carbonate). Thus, the saturation of carbonate ions in the water is vital to their survival. The increased amount of carbon dioxide in ocean water has shifted the chemical equilibrium such that there is a decreasing concentration of carbonate ions. Studies have shown that pteropods tend to have a slower rate of calcification when placed in water with a high concentration of carbon dioxide. To make matters worse, the decrease in carbonate ions also pushes the saturation horizon closer to the surface of the ocean, reducing the amount of water that pteropods are able to inhabit (calcium carbonite and aragonite will dissolve if placed below the saturation horizon). In addition to problems with building shells, pteropods face a few other potential roadblocks due to ocean acidification. First, they might have to adjust to a new diet; phytoplankton, pteropods’ main food source, will also be negatively affected by ocean acidification, and therefore pteropods could potentially have to deal with either a lack of phytoplankton or a change in what types of phytoplankton they are limited to consuming. Second, they, like many other marine organisms, will have to work harder to regulate bodily processes. The changes in pH of ocean water make it more difficult for pteropods to maintain the proper internal pH; acclimating to the new environment requires energy (which could be put towards other important processes). The combination of all of these roadblocks puts pteropods at risk.

Unfortunately, the risk extends beyond just pteropods. Ocean acidification ultimately threatens the balance of existing plankton species. Studies have shown that some species of plankton are less susceptible to changing ocean chemistry than others; this means that there will be winners and losers amongst plankton species over the next series of decades, resulting in a decrease in biodiversity. This, in turn, will send waves up the food chain. For example, pteropods make up a major part of the diets of certain types of salmon in the arctic (over 60% in some cases), so a decrease in the pteropod population could potentially do serious damage those salmon populations. Possibilities such as this are frightening, especially when considering that it is just one example of what ocean acidification is capable of changing; the situation that pteropods face is a mere microcosm of what could happen to the ocean’s ecosystem as a whole.

Sources:

Websites:

http://www.up.ethz.ch/education/term_paper/blank_termpaper_fs07_final.pdf

http://en.wikipedia.org/wiki/Zooplankton

http://en.wikipedia.org/wiki/Pteropoda

Book:

National Research Council. Ocean acidification: a national strategy to meet the challenges of a changing ocean. Washington, D.C: National Academies Press, 2010. Print.