EarthLabs > Climate and the Carbon Cycle: Unit Overview > Lab 7: Ocean Acidification: Too Much of a Good Thing? > 7B: Ocean Acidification - A Risky Shell Game?

Ocean Acidification: Too Much of a Good Thing?

Part B: Ocean Acidification: A Risky Shell Game?

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. Will all species respond to ocean acidification in the same way? Will some species adapt and others not? Find out how scientists are trying to answer this question in a laboratory setting:

As you read the article and explore the interactive, make note of the types of organisms they tested and how they responded to increasing amounts of CO2. Record them in the table your teacher gives you. Your teacher may decide to assign each group specific organisms.

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 respond 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. Because the sea floor is teeming with Echinoderms, scientists believe that Echinoderms are one of the biggest contributors to the movement of carbon from the biological pump into sea floor sediments. 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. Hofmann describe her own research on sea urchins and ocean acidification.


Get started on your research!

Your Research Question: Does ocean acidification inhibit the ability of sea urchinsa type of Echinodermto build their internal and external skeletons?

Your experimental hypothesis: Develop an experimental hypothesis after you have reviewed the life cycle of sea urchins and how they build their internal and external skeletons.

  1. Explore the sea urchin life cycle interactive and see a short video on sea urchin development created by Stanford University at VirtualUrchin Part One (more info)
  2. Enter the "Acid Ocean" website by clicking on the arrow in the bottom lower right corner.
  3. 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

Your Experimental Design:

  1. Sea Urchin eggs collected from off the coast of California will be raised in two different pH environments – a 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.
  2. When the sea urchin larva have reached their juvenile stage, you will measure the lengths of their two internal spines.
  3. Next, you will graph and analyze your data. Your teacher may have you combine the data from the entire class on a 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.




Post-Lab Discussion

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:

Optional Extensions

Read more about ocean acidification at these sites:

Read more about Dr. Gretchen Hofmann's work at these sites:

Explore the predicted effects of increasing ocean acidification on coral reefs using this NOAA interactive. Understanding Ocean Acidification Simulation

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.


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