EarthLabs > Corals > Lab 5: Trouble in Paradise: Factors that Impact Coral Health > 5C: Impact of Climate Change on Coral Reefs

Trouble in Paradise: Factors that Impact Coral Health

Part C: Impact of Climate Change on Coral Reefs

Scientists monitor coral health in a variety of ways. Sometimes they are able to take direct measurements, but at other times they must rely on remote measurements taken by satellites or on indicators such as ocean temperature or the presence of algal bloomsalgal blooms: the rapid excessive growth of algae, generally caused by high nutrient levels. Algal blooms can result in decreased oxygen in a body of water when the algae die, threatening the health of local marine life..

The rise of global temperatures due to increased levels of greenhouse gasesnamely carbon dioxide in the atmosphere is a major concern around the world. But did you know that as the amount of CO2 in the atmosphere increases, the amount of CO2 in the oceans rises as well? In fact, estimates indicate that the oceans have absorbed as much as 50% of all CO2 released into the atmosphere by human activity since 1750. What does this mean for ocean life and coral reefs in particular?

  1. Explore what happens to the ocean when CO2 content increases.
    • 300 mL bromothymol blue (a dye used as an acid-base indicator) aqueous solution
    • 500 mL beaker
    • drinking straw
    1. Pour the bromothymol blue solution into the beaker. Observe the color of the solution.
      When a bromothymol blue solution is neutral (like pure distilled water), the it will appear green. If the solution is slightly basic, the solution will appear blue. If the solution is acidic, it will appear yellow.
      Bromothymol Blue pH indicator dye in an acidic, neutral, and alkaline solution (left to right).

    2. Take a drinking straw and place it into the solution.
    3. Exhale through the straw into the solution. BE CAREFUL NOT TO INHALE ANY OF THE SOLUTION!
    4. Keep blowing into the solution until you see a change in color.

    Checking In

    • What happened to the bromothymol blue solution when you added carbon dioxide?


    Stop and Think

    1:Based on what you observed in the experiment, what do you think the effect of increased carbon dioxide levels has on the ocean? What consequences might this have for coral reefs?



  2. Look at the image below showing the ocean's involvement in Earth's carbon cycle.

    Earth's Carbon Cycle
    Annual flow of carbon between the atmosphere and oceans (billion metric tons). Image source: NOAA.


    Checking In

    • Based on the diagram, what is the net annual carbon intake of the oceans?
      2 billion metric tons

  3. Read the NOAA article What is Ocean Acidification? to learn more about how rising amounts of carbon dioxide in the oceans are predicted to affect coral reefs.
    Past and Projected Ocean pH
    Past and projected ocean pH levels. Image source:www.ocean-acidification.net/OAdocs/FS7_oceanacidification.pdf



    Checking In

    • How have the oceans minimized some of the impacts of global warming?
      By absorbing 525 billion tons of carbon dioxide from the atmosphere.
    • What are the projected impacts of ocean acidification on coral reefs and other marine organisms?
      When CO2 reacts with seawater, the pH of seawater is reduced, as is the availability of carbonate ions, which are important for the formation of the calcium carbonate shells of a number of marine organisms such as corals, marine plankton, and shellfish.


    The change in ocean chemistry brought about by CO2 acidification poses more of a threat to coral reefs than simply diminishing the amount of carbonate ions available for reef formation. The higher acidity of seawater can also be damaging to existing reef structures. Think back to Part 3A when you added vinegar (an acid) to the calcium carbonate precipitate. A similar, though slightly less exaggerated result will happen to coralsas acidity rises, coral reefs and other calcifying ocean organisms will actually begin to dissolve!


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