This paper was written as part of the 2009 Alaska Oceans Sciences Bowl high school competition. The conclusions in this report are solely those of the student authors.

Cause and Effect of Ocean Acidification

Authors

Tessa Hasbrouck
Kristin Neuneker
Rachael Satterwhite
Stephanie Randrup
Erin Streuli

Team Wise Outlandish Aquatic Apprentices (WOAA)

Petersburg High School
PO Box 289
Petersburg, Alaska 99833

Abstract

Ocean acidification, or the decreasing pH levels in the ocean due to carbon dioxide from human sources, is an issue that is arising in our Alaska waters today. Through a series of causes and effects, carbon dioxide that is being produced by human's burning of fossil fuel is changing the ocean's food web in and around Petersburg, Alaska. The food web is the hierarchy of organisms that rely on each other to survive. Specific organisms, such as clams, crabs, squid, mussels and corals, are in danger due to ocean acidification. When dealing with ocean acidification it is important to understand how the dissolved carbon is moved throughout our oceans by what is known as the conveyor belt. The interaction of carbon dioxide, the nitrogen cycle and the phosphorous cycle, will reveal how carbon dioxide affects all of the food web by starting at the base, phytoplankton. However, there is a way to begin decreasing the amount of carbon dioxide that is released into the atmosphere and therefore the ocean. Various policies, including taxes on each ton of carbon dioxide put into the atmosphere and grants for fishers who make their boats more efficient, are just a few ways to decrease the level of carbon dioxide that is being released into our atmosphere and our oceans. Ocean acidification could easily change the ocean and its chemistry, changing community structure in ways unknown.

Introduction

How often have you wandered into a kitchen to find the smell of savory, white king salmon taunting your nostrils? Does the sound of the cracking of the shell of a huge, freshly caught king crab call your family to the table? Do you live in a place where anyone who dislikes seafood is scorned, or those who are allergic to those precious delicacies of the sea are pitied? Petersburg, Alaska is one of the many places in this world, where all of the above are normal, along with the following: clam digging is a favorite hobby among many and a party isn't a party unless there is smoked salmon dip. Now, let us imagine a world without seafood. Outdoor activities that draw the attention of both adults and children are no longer possible. Not only is there a lack of delicious flavors in your palate, but the majority of your friends and family are unemployed because they were once fishers. Since Petersburg's economy relies on fish, the community would be significantly impacted.

Some may think that fish will always be an abundant resource and therefore it is unnecessary to imagine a world without it, but this is debatably not the case. The ocean is very complex, and has many mysteries for the myriad scientists studying its depths. The ocean is full of different organisms, from the bottom of the food chain, the plankton, to the carnivores of the deep, the giant squids. All organisms are able to adapt to different environments but perhaps not well enough to survive anything within the time frame of centuries rather than millennia, especially due to human interference. Humans burning fossil fuels is contributing to ocean acidification—one of the issues affecting oceans. The following information is a preview of the possible dangers of changing amounts of chemical species in the ocean and how they affect different organisms, specifically in and around Petersburg, Alaska.

In this research paper, we will be focusing on how ocean acidification affects the population of Petersburg directly. In order to do this, ocean acidification will be defined. To define ocean acidification, it is also important to understand how carbon moves throughout the oceans and how carbon interacts with the nitrogen and phosphorous cycles. Most importantly, this paper will reveal how ocean acidification affects the food web and specific species local to areas around Petersburg. With every issue that arises, there is generally a solution to fix it. We will conclude with policies that will provide a method to decrease the amount of carbon dioxide in our atmosphere and therefore maintain our pristine, Alaska oceans.

Basis of Ocean Acidification

Ocean acidification results from the process of carbon dioxide dissolving in seawater that causes a reduction in ocean pH and a shift in carbonate speciation. Measurements of carbon dioxide in seawater have been collected since the beginning of the nineteenth century but did not produce many results until the mid-twentieth century. Then they dismissed the possible large impact that rising amounts of atmospheric carbon (CO2) would have on the ocean biota (Doney 2006). Recent studies are beginning to show the impact atmospheric carbon is having when combining with the carbon already present in the ocean: "About a third of the carbon dioxide released by the burning of fossil fuels will currently end up in the ocean" (Doney 2006).

When the CO2 dissolves in the ocean it forms carbonic acid in the seawater, which lowers the pH level. The pH level is currently somewhat alkaline at 8–8.3, but is about 0.1 lower than what it was before the industrial revolution. Ken Caldeira, an oceanographer at the Carnegie Institution of Washington, suggests that ocean pH several centuries from now will be lower than at any time in the last 300 million years (Doney 2006).

When CO2 dissolves in water: CO2 + H2O←→H2CO3←→HCO3- + H+←→CO32- + 2H+, an increase of H+ decreases the pH level of the ocean. Carbon dioxide being dissolved into the seawater also decreases the concentration of carbonate ions (CO32-). The amount of carbonate ions, which is expected to drop by half over this century, will lessen and hurt the ability of some organisms to make calcium carbonate. This will cause organisms with shells such as snails, oysters, zooplankton species and coral to be unable to grow shells or the ones who already have shells to lose them as the shells may start to disintegrate (Doney 2006).

Oceanic Carbon Transport

In order to understand how ocean acidification impacts marine organisms and eventually, Petersburg, we need to understand the conveyor belt, which is a current that transports dissolved carbon dioxide all over the world. This conveyor belt is a main source for circulating the waters, but this also means that it contains all of the particles in the waters. Carbon dioxide emitted from dead organisms is a natural occurrence and the conveyor belt of the ocean picks up this natural carbon dioxide when these dead bodies decompose. When the conveyor belt returns to the surface it gathers additional atmospheric carbon dioxide produced by human use of fossil fuels. This causes the conveyor belt to obtain much more CO2 than it otherwise would have (Catchpole 2008).

The conveyor belt is the predominant force in ocean circulation and sustains marine life. This mainstream current is driven by colder, dense water as it sinks to the floor of the ocean at the polar ice caps (Ocean Champions). The conveyor belt is a stream of current that carries waters of the different oceans all over the world and it also brings warm waters up toward the ice caps so that it can cool. This is where more ocean acidification takes place (Lippsett 1997). When the water is colder, it can dissolve more carbon dioxide and therefore more ocean acidification will occur in these areas (Australian Government 2008).

There are different types of currents in the ocean besides the conveyor belt. There are surface currents, which are in the upper 400 meters of ocean, and there are deep-water currents, which are below 400 meters. The shallow currents are strongly influenced by wind while deep currents are driven by their density and by gravity. The different temperatures and the salinity of the ocean determine the densities of the deeper waters (Stott). Because of these currents, research has shown that the more acidic waters that contain more of the carbon dioxide are moving closer up along the western coast and this is starting to affect Oregon, California, and Canada. These waters are moved by a process called upwelling whereby deep waters hit the continental shelf and move to the surface. This water is cooler and saltier and it also contains more acidification than the surface waters (Catchpole 2008).

Along with lower temperatures holding a greater concentration of dissolved carbon dioxide, freshwater behaves in a similar fashion. In the Gulf of Alaska, ocean acidification might occur more rapidly due to the freshwater inputs from the heavy precipitation, melting snow, and streams from the mountains that lead to the ocean waters. With more ocean acidification in the Gulf of Alaska, marine life may be affected differently—or more rapidly—in this area than in other areas studied (Merrigan 2008).

Possible Feedback Loops—Interaction with the Nitrogen and Phosphorus Cycles

Two of the most necessary chemicals found in the ocean are the elements nitrogen and phosphorous. Although many organisms require nitrogen to survive, it cannot be used in most forms. A large percentage of nitrogen comes from run-off from the land. Phytoplankton, the building block of the food web, are organisms that heavily rely on phosphorous and nitrogen (NOAA 2007). However, the amount of nitrogen and phosphorous limits the growth of population of phytoplankton, therefore limiting the other parts of the food web. The amount of phytoplankton corresponds with the amount of nitrogen available. The more nitrogen and phosphorous available in the ocean, the more carbon dioxide that will be taken in by the phytoplankton. The atmosphere has high levels of carbon dioxide, whereas the ocean has a lower concentration of carbon dioxide. Therefore, carbon dioxide will continue to move from the area of higher concentration to the area of lower concentration. Phytoplankton acquires CO2 through the process of photosynthesis. This creates a short-term negative feedback loop and is dependent on the amount of nitrogen and phosphorous in the ocean.

Impacts on Organisms and Food Web

The marine ecosystems hang on a delicate balance; every organism depends upon another to survive. This interdependence is most visible in a food web. The base of the food web is composed of the producers. Multiple food chains consisting of producers, primary consumers, secondary consumers up to the top predators form the food web. There are over 100 different illustrated food webs in the marine ecosystem (Trites 2003). These marine food chains are generally very short, spanning 3 or 4 creatures (Trites 2003). If something were to happen to their main food source the organism would have to rely on another food source or be excluded. Most organisms need to consume about 3–10 times more than they produce and they pass on only about 70%–95% of their energy (Trites 2003); in other words, a greater expenditure of energy to find food may affect the growth and development or reproductive abilities.

Ocean acidification is the process of increasing the carbon dioxide levels of the ocean, making it become more acidic. Carbon dioxide from the atmosphere is being absorbed by the oceans, approximately 1/3 of it is absorbed (Doney 2006). When carbon dioxide combines with salt water it forms carbonic acid, a substance that gives off hydrogen ions making the seawater more acidic (Doney 2006). The hydrogen ions combine with carbonate ions, form bicarbonate, and remove carbonate.

Calcium carbonate is a main structural component of many marine organisms. Ocean acidification will lower pH levels in the water and make carbonate harder to come by. This causes destruction among creatures that need calcium carbonate to sustain life. The lack of carbonate combined with lower pH levels will cause a build up of carbonic acid in the body fluids of organisms. This build up of acid may affect physical behavior and reproduction rates (Hood 2008).

For marine animals, the pH of today's surface ocean is starting to push that envelope. With a pH ranging from 7.5 to 8.5, it is becoming more acidic (Raven et al. 2005). This water is saturated with calcium carbonate, which is a very important organic molecule for organisms like mollusks, corals, and crustaceans that make shells. The amount of CO2 on the surface of the water is much higher then it should be. As the CO2 reacts with the saltwater, it lowers the pH and releases hydrogen ions. The released hydrogen ions bind with carbonate, preventing it from forming calcium carbonate molecules, which are very important for shellfish (Raven et al. 2005).

At the base of the marine food chain are zooplankton and phytoplankton, some of which would suffer from ocean acidification. Calciferous organisms, like some planktons, need calcium carbonate to create their structures. In the presence of acidic environments, the plankton would have trouble finding enough calcium carbonate to create these structures. It's almost like these organisms are dissolving. If these planktons were harmed, it would cause issues all the way up the food web.

A crucial organism that depends on calcium carbonate is the pteropod. Pteropods are small planktonic mollusks that are also near the bottom of the food chain. They are predicted to be one of the first casualties of increasing acidity in our marine waters (Schoof 2008). These pteropods are a key food source for salmon and other species (Schoof 2008). Without planktons, such as pteropods, we may see an impact upon salmon, halibut, mackerel, and cod. All these fish feed on the many small types of plankton that may be dissolved from ocean acidification (Jennifer Hawks 2007). If the producers or primary consumers are harmed then the predators who consume these producers will also be impacted.

Squid (Doryteuthis plei) may be harmed from this lowering in pH because it lowers the oxygen levels of the water. In order to swim well, squid need a lot of energy; for this energy to be obtained the water needs to be well oxygenated. If there is a lower pH due to ocean acidification, this energy may not be as readily produced. This will also affect the animals that need squid to survive, the ones that eat these squid will have a diminished food supply due to the necessity of the food chain (Other Marine Animas? 2008).

King crab (Paralithodes camtschaticus) is another organism that could be profoundly impacted by ocean acidification. These crabs are calcifying organism, which rely on the calcium to build and repair themselves. With the more acidic water these crabs could lose their ability hunt, reproduce, and avoid predators. Their shells could possibly dissolve from the acidic water, leaving them weak or dead (Warren 2007).

Larval clams (Protothaca staminea) cannot tolerate long exposures to pH levels that are very acidic. In the case of very acidic waters, these clams could not survive because their shells would dissolve (Green 2007). Clams play a crucial role in the survival of sea otters. Without clams, sea otters would be left starving.

One group of organisms that may be in more danger than we thought is the mussels within the genus Pteriomorpha. In a recent article published in Discover Magazine, it states that the ocean acidification process is rapidly increasing (2008). During a study performed near Washington state, the rapid increase was apparent and the mussel population was greatly diminished. Mussels have calcium carbonate shells that are weakened or dissolved due to the acidity from the water. This will be felt throughout the food chain as large numbers of a species that everything depends on are diminished (Ocean Acidification 2008).

Another harmful affect possibly caused by ocean acidification is the inability of some species of fish to have proper otolith formation (Kita and Ishimatsu 2004). An otolith is a sensory organ that fish like the Japanese flounder use for balance and hearing (and halibut and salmon). This organ is composed of aragonite, a substance that is dissolved very simply in acidic saltwater. This organ is not known to be affected by ocean acidification directly, but evidence supports that it is.

In addition to possible impacts to the food web, habitat that bottom fish such as rockfish depend on are impacted. Corals have been shown to suffer from the effects of lowered pH in the water (Hood 2008). Corals in Southeast and around the world provide safe habitats for small fish and make it easier for them to hide from predators. If these corals are immersed in this acidic environment they will deteriorate and become no longer habitable. This would cause a drop in numbers of smaller species such as animals that are hunted by larger predators; it would prevent them from having a place to hide (Hood 2008).

Coralline algae are commonly found in reef communities and are characterized by a thallus that is hard from the calcareous deposits that are contained within the cell walls. Coralline algae play a very vital role in the ecology of the coral reefs. Sea urchins eat the coralline algae along with certain mollusks. The algae also produce important chemicals that help promote herbivorous invertebrates. These in turn keep various seaweeds from growing, which would be competing with the algae (Coralline Algae 2008). Ocean acidification could possibly deteriorate the supply of the algae, which would leave sea urchins and mollusks hungry and leave the coral bare (Coralline Algae 2008).

Suggested Policy Changes

Along with impacting food webs and community structure, ocean acidification impacts humans—a top predator. Eating wild fish is one of the healthiest things to eat, but with the growing ocean acidification that could change. As a community we are responsible for our wastes; carbon emissions included. If we were to educate people about ocean acidification and provide concrete evidence to support what we are teaching, then our community will listen and be more cooperative with our policy suggestions. The cause of ocean acidification is related to carbon emissions (IPCC 2001). We can individually reduce carbon emissions by doing things like changing light bulbs to incandescent bulbs, or unplugging your electronics when they are not being used.

As a state, Alaska offers loans at a low rate for fishers who are improving the quality of their boat in such a way that it would become more efficient. Possibly they could offer grants instead of loans. This would make it even more enticing for fishermen to fix their boats and decrease carbon emissions. Grants would provide many fishermen with the necessary tools and equipment to make their boats more efficient. This would lessen communities' carbon emissions, such as ours, that have a large fleet. Growing up with a fishing family and in a fishing community we realize that fisherman don't like to be told what they have to do with there boats, therefore this grant proposal will offer them a situation where they can benefit without having to follow rules set by someone else. This would be a lot of money but it would be hugely beneficial. One of our states main industries is fishing and with the presence of ocean acidification we are hanging our futures on a delicate balance. In order to save our oceans and our industries we should do everything possible.

Alaska has long been a standard for national fisheries management and policies. We recommend that the nation follow the same use of loans provided for making a more energy efficient fleet. If Alaska is successful with the grant program then our nation would be even more likely to follow our lead. This could have exponential effects through the entire nation. This could even lead to other countries following us to help lower the carbon dioxide being put into the ocean. With the help from all the countries maybe we could slow down the progress of ocean acidification.

Another suggestion for cutting back the carbon dioxide emissions in the air to try and reduce ocean acidification would be to place a tax or a fee for each ton of carbon dioxide that is emitted for each ton of the carbon that is contained in the fossil fuels. If we were to employ this method of reducing CO2 emissions then it would encourage companies to cut back on their carbon dioxide emissions so that they would not have to pay the tax if the cost of doing so was less than the cost of paying the tax (Orzag 2008).

Conclusion

Ocean acidification is not something that will start to largely impact our world tomorrow. Ocean acidification will have long-term implications for the world in ways not yet known due to the slow process of change and the resiliency of the oceanic ecosystem (NOAA 2008). This idea should not change your view of this everlasting cycle. Ocean acidification has come 30 years earlier than it was expected to and if the emissions continue at the same current rate that they are going right now, scientists predict that the ocean levels of pH will drop from 8.1 to 7.7 by the year 2100 (Mongabay 2008).

Imagine a world a hundred years from now when you cannot even go for a leisurely swim or dive into the ocean, a world where a giant Humboldt squid rules the waters. As the ocean grows more acidic these squid appear to be growing in numbers. "It has probing arms and tooth-lined tentacles, a raptor-like beak and an insatiable craving for flesh—any kind of flesh, even that of humans. This squid growing in numbers is likely to change the community structure in unknown ways…[they] may expand northward eating their way through fisheries as they go" (Thomas 2007). This impact on fisheries and fisherman can change communities along the coast for either the better or worst. Not much is known by scientists about these large creatures as they spend most of their lives at depths of 650–3,000 feet. One thing is certain, ocean acidification is changing things for creatures of the ocean, some for the better such as these squids who thrive with it, and some who are on the bad side of it, such as snails or other creatures who use calcium carbonate for shells or skeletal structures.

Figures

Pacific oyster eggs

Figure 1.Crassostrea gigas after 48 hours incubation. Frame a is the control. It was incubated in standard seawater (8.2 pH). Frames c, e, and g were incubated in pH 7.4 seawater (Kurihara, 2007).


References Cited