EarthLabs > Climate and the Carbon Cycle: Unit Overview > Lab 7: Ocean Acidification > 7B: Ocean Acidification - A Risky Shell Game?

Ocean Acidification

Part B: Ocean Acidification - A Risky Shell Game?

Ocean acidification can impact marine organisms in a variety of ways

Scientists are only beginning to do the research on how individual species of organisms might respond to increasing levels of ocean acidity as atmospheric levels of CO2 continue to rise. How will ocean acidification impact Earth's biodiversity? Will all species respond to ocean acidification in the same way? Will some species adapt and others not? To try and find answers to some of these questions, first watch the video "Demystifying Ocean Acidification and biodiversity." As you watch, take notes on how ocean acidification can affect different types of marine organisms.

If the video does not play, you can watch it here: Demystifying ocean acidification and biodiversity impacts - Global threats to biodiversity - Khan Academy


Share your list of how ocean acidification can affect different types of marine organisms with the class.

Next, read how scientists at Woods Hole Oceanographic Institute and Marine Laboratories are trying to answer some of the puzzling questions of ocean acidification's effects on biodiversity.

  1. Read the Oceanus article Ocean Acidification: A Risky Shell Game. This article reviews the results of lab investigations on the effects of increasing concentrations of atm CO2 on several different species of marine organisms.
  2. Read carefully paragraphs 4 and 5 to understand how they set up their experimental tanks.
  3. Make a 4-column table in your lab notebook with the following headings:
    • name of organism
    • temperate or tropical environment (if available)
    • concentration of atm CO2 exposure (e.g., 400 ppm, 600 ppm, 900 ppm, 2850 ppm)
    • responses to increased acidity
  4. Make sure you read both the main article and the slide show of article images pictured on the upper right. As you read, make note of the names of organisms they tested and how they responded to increasing amounts of atm CO2. Write this information in your table.
  5. Explore the interactive (Learn How Animals Build Their Shells) embedded in the article. This interactive will help you understand the chemical relationship between carbon dioxide, shell-building, H+ ions, and ocean acidification. NOTE: You need a Flash-enabled device to explore this interactive or the Earthlabs App as described below.

To view this interactive on an iPad, use this link to download/open the free TERC EarthLabs App.

Checking In

  • What levels of atmospheric CO2 did scientists expose the marine organisms to in their experimental design? Why did they choose these levels of atm CO2?

    Researchers exposed the marine organisms to 400 ppm atm CO2 (current levels of CO2), 600 ppm CO2(predicted in a hundred years), 900 ppm CO2 (predicted in 200 years) and 2850 ppm (a very high level expected to dissolve shells). You now know that increased levels of CO2 in seawater will make the water more acidic. By bubbling different amounts of CO2into aquatic tanks with shelled marine organisms, researchers were able to create test environments with different pH values.

  • Why do shell-builders have to pump H+ ions out from their tissues and back into seawater?

    The H+ ions like to chemically combine with carbonate ions to form bicarbonate compounds. This makes the carbonate ions unavailable to combine with calcium to produce calcium carbonate compounds, which shell-builders need to build their shells.

Stop and Think

1: From the article, choose two types of marine organisms that responded differently to increasing ocean acidification. Compare and contrast them in terms of how they responded to increasing ocean acidity.

Now its your turn to do some research of your own!

In Lab 6A, you learned that the ocean's biological pump sequesters large amounts of carbon dioxide in shell-building organisms that eventually die, sink and become part of deep ocean sediments for very long time scales - thousands to millions of years.

Could ocean acidification inhibit the oceanic biological pump by reducing the ability of shell and skeleton builders to sequester carbon? If so, what might happen to other components of the carbon cycle?

To research answers to these important questions, you will take on the role of a marine biologist studying the effect of ocean acidification on Echinoderms, a group of marine organisms that includes star fish, brittle stars and sea urchins. Echinoderms take calcium carbonate out of the seawater and use it to make their internal and external skeletons. As seen in the video below, the sea floor is teeming with Echinoderms.

For this reason, scientists believe that Echinoderms are a significant contributor to the movement of carbon from the biological pump into sea floor sediments.(M. Librato For your research, you will be studying the effects of ocean acidification on sea urchins, a specific group of Echinoderms. Dr. Gretchen Hofmann, a marine biologist, is a leading researcher on the effects of ocean acidification on sea urchins.


Before you begin your own research, listen to Dr. Hofman describe her research on sea urchins and ocean acidification.

If the video does not play, watch it here: Science Bulletins: Acid Oceans - YouTube

Review the life cycle of sea urchins and how they build their internal and external skeletons.

  • Explore the sea urchin life cycle interactive and see a short video on sea urchin development created by Stanford University at Virtual Urchin Part One.
  • Enter "Our Acidifying Ocean" by clicking on the arrow in the bottom lower right corner.
  • Next, click on "cycles" in the menu at the bottom. This will take you directly to the life cycles of sea urchins interactive. You can also view a video on sea urchin larval development from the Plankton Chronicles Website or Plankton Chronicles-Vimeo.
Develop an experimental hypothesis to answer the research question:
Does ocean acidification inhibit the ability of sea urchinsa type of Echinodermto build their internal and external skeletons?

Virtual Urchin Lab Activity

Sea Urchin eggs collected from off the coast of California will be raised in two different pH environmentsa pH of 8.1, which represents ocean pH conditions today, and a pH of 7.7, which is predicted within the next 100 years if CO2 emissions continue to rise. When the sea urchin larva have reached their juvenile stage, you will measure the length of one of the urchins two internal spines(arms). Next, you will calculate the average arm length for each experimental group of larvae. (or larva from the entire class) Note: Your teacher may have you combine the data from the entire class on a class data table. If so, you will determine your average from this class data.

  1. Enter The Virtual Urchin Part Two and click Part 2 at the upper right to begin the experiment.
  2. Work in the Virtual Urchin Laboratory until you reach the Graphs: Interpreting Results section in Part 3.
  3. Copy the data table, graph your data, and include with your written conclusion. If your teacher has the class combine the data from the entire class on a class data table, then you will base your analysis on the class data table.
  4. Write a conclusion:
    • Summarize your experiment.
    • Discuss and interpret the results. Explain how the evidence from the lab supports or refutes your hypothesis.


Think about Dr. Hofmann's research and about your results from exposing the sea urchins to a more acidic pH. Then, discuss possible answers to the following questions:
  • How might exposure to a more acidic pH affect the growth, development and reproduction of sea urchins?
  • If exposure to a more acidic pH caused a decline in some sea urchin populations, how might this affect the storage of carbon in ocean sediments? Why?
  • What additional research do you think would need to be done to fully explore the effects of ocean acidification on the oceanic biological pump?

Optional Extensions

Want to find out more about ocean acidification? Check out these resources:

  • Explore the predicted effects of increasing ocean acidification on coral reefs using this NOAA simulation. Understanding Ocean Acidification Simulation
  • Watch the NOVA video Lethal Seas.
  • Watch Acid Test Note: There is a misconception in this video that oceans will become an acid. Oceans will become more acidic as more CO2 is absorbed, but oceans will not become an acid.