Changing Planet: Fading Corals


Students use various references to learn about coral ecosystems, and then use online tools to understand the impacts that a warming ocean has on these ecosystems. Student teams select different coral reefs around the globe and report the status of their coral reef ecosystem at a "Coral Reef Roundtable."

  • Student worksheet
  • Limewater
  • Straw
  • 2 Beakers or clear classes or cups
  • vinegar
  • eyedropper
  • filter paper
  • Computer and internet access, ideally for each student
  • Digital images of corals and coral reef ecosystems
  • Presentation software such as PowerPoint

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Adapted by NESTA/Windows to the Universe team members Missy Holzer, Jennifer Bergman, and Roberta Johnson from resources on Windows to the Universe as well as an Earth lab activity. Information/data/maps provided by ReefBase ( M. Tupper, M.K. Tan, S.L. Tan, M.J. Radius, S. Abdullah. ReefBase: A Global Information System on Coral Reefs [Online]. Available from: [Accessed: February 16, 2011].

Grade level:

6-9, although it can be adapted for higher and lower grades by adjusting the content

  • Introduction: 30 minutes
  • Part 1: Student research: 1 class period & homework
  • Part 2: Data interpretation: 1 class period
  • Part 3: Reef Roundtable presentations & wrap-up: 1 class period
Student Learning Outcomes:
  • Students synthesize references on corals to describe the life cycle and living requirements of corals.
  • Students will apply what they learned about coral reef ecosystems to the interpretation of spatial data. The data includes the global characteristics of coral reef ecosystems, the global distribution of coral reef ecosystems, and the current health of coral reef ecosystems.
Lesson format:

Research inquiry, map & data interpretation

Standards Addressed:

  • National Science Content Standards 5-12: Abilities necessary to do scientific inquiry
  • National Science Content Standards 5-8: Populations and Ecosystems
  • National Science Content Standard 9-12: Interdependence of organisms


  1. For background information on the consequences of warming oceans and other threats to coral reefs watch Changing Planet: Coral Reefs. Also, explore these topics on the Windows to the Universe website using the links listed below.
  2. Gather demonstration materials and print out the student worksheet. Introduce the topic with a brainstorming session listing what students already know about corals, and use this content to determine the extent of the background research needed by students to understand the creation and sustainability of the coral reef ecosystems. Create and show a slideshow of corals and coral reef ecosystems to encourage student thought about the elements of these ecosystems as well as the biodiversity inherent of these ecosystems. Many of the links below have coral and coral reef ecosystem images that can be used for a slideshow. Be sure to follow all copyright rules and to properly cite all borrowed images.
  3. Provide students with a list of on online references such as those listed below, and have them work in small teams (no more than 4 students) to research key information about corals and coral reef ecosystems. Allow them one class period to gather this research and tell them that they will not only be assessed in the quality of what they found, but that they will need this information for the next part of this lesson. They may need time outside of class to complete this task.
  4. Students may question how coral reefs grow, and this small demonstration may help them understand the process. Ask students what coral reefs are made of. Write the molecular formula of calcium carbonate (CaCO3) on the board pointing out corals must obtain calcium from somewhere in order to grow. Pour some limewater in a beaker or a clear glass or cup, and ask a student to gently blow into the limewater solution with a straw (caution them not to draw the limewater up into the straw). The solution will become cloudy, demonstrating the presence of calcium as an insoluble precipitate. Gently pour the solution through a filter paper, collecting the solid material on the filter paper. Allow the filter paper to dry, and test for the presence of calcium carbonate by dropping a couple of drops of vinegar on the solid. This will cause the solid to bubble demonstrating the presence of calcium carbonate. The formula for the reaction of carbon dioxide and limewater is: Ca(OH)3(aq) + CO2(g) ⇒ CaCO3(s) + H2 O(l). Corals produce carbon dioxide during respiration which in turn is used by the algae living in the coral during photosynthesis. Additionally, some carbon dioxide reacts with seawater in the coral polyps' stomach to produce a form of calcium carbonate called aragonite. The aragonite is secreted by the coral to build the coral skeleton.
  5. Tell students that they will be preparing a status report of a selected coral reef ecosystem in a later class period during a "Coral Reef Roundtable", and in order to prepare for this they will need to learn how to interpret online data and maps. Be aware that depending on the age of the student and their abilities, they may need assistance in spatial data interpretation at global, regional, and local levels. Prepare for this by locating and showing students images of the same location at these scales. Ask them to interpret what they see at each of these levels, and listen and assess student interpretations so that modifications to this lesson can be made as necessary.
  6. In order to coach the students in the use of spatial data, familiarize yourself with Reef GIS maps and the data used to create the maps. In Part 2 of this lesson, students explore the capabilities of Reef GIS, and in Part 3 student teams use the available data of a chosen reef ecosystem to create their report for the Coral Reef Roundtable. You may want to limit this lesson to a specific global region such as the Caribbean, Florida Keys, Indonesia, or Australia, and if so, pre-select a number of coral reef ecosystems from the global region to use in the lesson. Require teams to inform you of which location they chose so that all teams are investigating different locations.
  7. After walking students through the data available and coaching them on how to use the tools such as the ruler and information, allow students time to explore the data available for their reef ecosystem using their new skills. Students should save the maps they create to be used in their digital presentations at the Coral Reef Roundtable. To assist students in creating presentations, provide a template or a list of what to include on each slide.
  8. Set up the classroom in a way that invites whole class participation in the Roundtable discussion. Have students create placards with the name of the location of their coral reef ecosystem to be used to identify each of the student research teams during the Roundtable discussion. Mention to students that the goal of the Roundtable is to inform each other of the status of the coral reefs around the world, and to identify key hazards to the health of the corals. Next, each team presents their findings, and after all the presentations, the entire class summarizes the findings into one report to be presented to the governments of each country involved. Have students select a student leader to facilitate this process, and assist this person in delegating the work. Let the students decide what the layout should look like and what content to include, although the Reef GIS maps should be included.


Students are assessed on the quality of their background research and in the skills they develop in the interpretation of the spatial data. Students should also be assessed on their preparation for and presentation at the Coral Reef Roundtable.


Remind the students not to inhale the limewater up the straw. Always use safe laboratory practices.


Discard used limewater down the drain with running water. Clean and properly store lab supplies for future use.


  • Students can use NOAA Coral Reef Watch data to monitor their selected reef system over a period of time. Reconvene the Coral Reef Roundtable at a later date and have them report on the status of their reef ecosystem. This website has spatial data as well as tabular data which can be displayed in graphical form.
  • The topic of ocean acidification should be tied into this topic using the Changing Planet: Ocean Acidification program, and the associated Windows to the Universe materials and lessons.


A coral reef is like an underwater city. Corals and algae construct the framework that rises off the tropical ocean floor and attract many diverse inhabitants. Schools of multicolored fish glide above the coral structure. Invertebrates dart around on this coral city. All that busy activity and life exists in a delicate balance.

Humans can threaten the delicate balance of a coral reef iin many ways.  Some of the threats are easy to see - plastic bottles and other trash littering reefs, sediment in the water or settling on the reef corals, and water pollution. Overfishing is reducing the number of grazing fish in some areas. And scratches on corals from the fins of careless snorkelers, anchors, or even deep gouges from boats that have run aground are visible in many reefs.

There are also threats that are less visible yet pose great dangers to coral reefs like acidic seawater, warmer seawater, and coral diseases. The threats might be hard to see, but their effects are not. Some reefs have been so hard hit that scientists say they will not be able to recover. Scientists predict that over half of the world’s coral reefs may die by 2050 if these threats continue.

Acidic Seawater: Increasing amounts of carbon dioxide are released into the atmosphere from burning of fossil fuels. Some of that carbon dioxide makes its way into the world’s oceans. This changes the chemistry of seawater, lowering its pH, making it more acidic, which could have a large impact on marine life in the future.

Marine creatures such as corals, clams, snails, and many types of algae and plankton build their skeletons and shells from calcium carbonate. These creatures get the chemical building blocks they need to form the calcium carbonate mineral of their skeletons from seawater. As seawater gets more acidic with more carbon dioxide dissolved in it, these creatures might have a harder time making their skeletons and shells.

Warmer Seawater: As the Earth warms, so do its oceans. Surface water temperatures obviously change from season to season and year to year, but the whole ocean has warmed about 0.1 degree Fahrenheit (0.55 degree Celsius) in the past 30-50 years. This may not seem like much of a temperature change, but it is quite significant. When seawater gets too warm, coral animals loose the algae that live within their little bodies, a process called coral bleaching. Without the algae, corals have less nutrition. Unless cooler temperatures return, allowing algae to return, the coral dies. So as water temperature climbs, corals become less healthy. Some reefs might be protected if there are areas of the ocean that are able to stay cool.

Coral Diseases: These diseases are caused by bacteria, fungi, and viruses. There are more diseased corals today than there were several decades ago. These diseases do occur naturally, but are also brought on by pollution (like waste water and sewage flushed down the drain and toilet) and other changes to the environment.

Coral disease can be the cause of mortality in coral, especially if the coral has been first weakened by bleaching. Though, coral disease has also happened without any bleaching being recorded first. Scientists are researching and debating the connection between global warming and disease; it is a complex picture, but one that seems to be gaining traction among scientists. Professor Drew Harvell, a professor of ecology and evolutionary biology at Cornell University and chair of the Coral Reef Targeted Research Program's Coral Disease Working Group said, "Associations between warming and infectious disease in corals are getting more established now. That Eastern Caribbean outbreak (2005) was massive, the biggest to occur in the region that we know of. My concern is that it's also a harbinger of things to come."

No one would argue with the idea that limiting greenhouse gases is good for coral reefs; limiting them would make the oceans less acidic and cooler in the long run which are both good for coral reef development and health. Humans should also curb known stressors to coral like contaminating pollutants, sewage, and sediment runoff that happens around development projects.

Corals are often mistaken to be plants. In reality, there are both soft and hard corals, but all of them are animals. Hard corals form coral reefs, which serve as a home for many sea creatures. Without them, many marine animals would become extinct. Hard corals have two parts: a hard outer shell called a corallite, and soft tissues called polyps. Corals are so pretty that some people make reef aquariums to enjoy in their homes.



Last modified March 2, 2011 by Missy Holzer.

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