Environmental Science: Ocean Acidification and Coral Reefs
How changing ocean chemistry affects reef ecosystems
Environmental Science: Ocean Acidification and Coral Reefs
How changing ocean chemistry affects reef ecosystems
Environmental Science - Grade 9-12
- 1
Explain how carbon dioxide from the atmosphere can lead to ocean acidification. Include the role of carbonic acid in your answer.
Think about the path from atmospheric CO2 to dissolved chemicals in seawater.
Carbon dioxide dissolves into seawater and reacts with water to form carbonic acid. Carbonic acid releases hydrogen ions, which lowers pH and makes the ocean more acidic. - 2
A seawater sample has a pH of 8.2. Another sample from the same reef 30 years later has a pH of 8.0. Explain why this is an important change even though the numbers look close.
The pH scale does not change in simple equal steps.
This is important because the pH scale is logarithmic, so a decrease of 0.2 pH units means a significant increase in hydrogen ion concentration. Even small pH changes can affect coral growth and reef chemistry. - 3
Corals build skeletons from calcium carbonate. Describe how ocean acidification can make it harder for corals to build and maintain their skeletons.
Ocean acidification reduces the availability of carbonate ions in seawater. Corals need carbonate ions to combine with calcium ions to form calcium carbonate, so lower carbonate availability makes skeleton building slower and can increase skeleton weakening. - 4
Write the simplified relationship between calcium ions, carbonate ions, and calcium carbonate. Then explain what happens when carbonate ions become less available.
Use words or symbols such as Ca2+, CO3 2-, and CaCO3.
The simplified relationship is calcium ions plus carbonate ions form calcium carbonate. When carbonate ions become less available, corals and other calcifying organisms have more difficulty forming shells and skeletons. - 5
A reef has 45 percent live coral cover in 2010 and 30 percent live coral cover in 2020. Calculate the percentage point change in live coral cover.
The live coral cover decreased by 15 percentage points because 45 percent minus 30 percent equals 15 percent. - 6
Describe one difference between coral bleaching and ocean acidification.
One process is closely linked to coral-algae relationships, while the other is linked to seawater chemistry.
Coral bleaching usually happens when stress, often high water temperature, causes corals to lose the algae living in their tissues. Ocean acidification is a change in seawater chemistry caused by dissolved carbon dioxide, which lowers pH and reduces carbonate ion availability. - 7
Scientists measure lower carbonate ion concentrations near a reef over several decades. Identify one likely cause and one likely effect on the reef ecosystem.
One likely cause is increased carbon dioxide dissolving into seawater from the atmosphere. One likely effect is slower coral skeleton growth, which can reduce reef structure and habitat for fish and invertebrates. - 8
Explain why coral reefs are important to both marine life and people.
Include at least one ecological benefit and one human benefit.
Coral reefs provide habitat, shelter, and feeding areas for many marine species. They also support fishing, tourism, shoreline protection, and cultural values for human communities. - 9
A student says, "Ocean acidification means the ocean is becoming acidic like lemon juice." Correct this statement using accurate scientific language.
The ocean is not becoming acidic like lemon juice. It is becoming less basic, meaning its pH is decreasing, but most ocean water is still above pH 7 and remains slightly basic. - 10
List two local stressors that can make coral reefs less resilient to ocean acidification, and explain one way to reduce either stressor.
Local stressors are problems that nearby communities can often help manage.
Two local stressors are nutrient pollution from runoff and overfishing of important reef species. Nutrient pollution can be reduced by improving wastewater treatment, limiting fertilizer runoff, and protecting wetlands that filter water. - 11
Design a simple field study to monitor possible ocean acidification effects on a coral reef. Name two variables you would measure and explain why.
A field study could measure seawater pH and coral growth rates over time. pH shows changes in ocean chemistry, and coral growth rates show whether reef-building organisms are having more difficulty forming calcium carbonate skeletons. - 12
Explain why reducing carbon dioxide emissions is considered a major long-term solution to ocean acidification.
Connect emissions, atmospheric CO2, dissolved CO2, and ocean chemistry.
Reducing carbon dioxide emissions lowers the amount of carbon dioxide entering the atmosphere and dissolving into the ocean. This helps slow the chemical changes that lower pH and reduce carbonate ion availability.