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Keeping Watch on Coral Reefs

Monitoring Coral Reefs / Grades 9-12 / Earth Science

Focus Question

Why are coral reefs important, and what can be done to protect them from major threats?

Learning Objectives

Links to Overview Essays and Resources Useful for Student Research


Audio/Visual Materials

Teaching Time

Seating Arrangement

Maximum Number of Students


Key Words

Remote Sensing


Background Information

Coral reefs are one of the most biologically productive ecosystems on Earth. Most people have seen images of brightly colored fishes and other reef-dwelling organisms, yet many do not understand why these systems are personally important. Programs and articles about coral reefs typically point out benefits that include protecting shorelines from erosion and storm damage, supplying foods that are important to many coastal communities, and providing recreational and economic opportunities. These benefits are obviously important to people who live near reefs, but there is another aspect of coral reefs that can benefit everyone: the highly diverse biological communities are new sources of powerful antibiotic, anti-cancer and anti-inflammatory drugs.

Despite their numerous benefits to humans, many coral reefs are threatened by human activities. Sewage and chemical pollution can cause overgrowth of algae, oxygen depletion, and poisoning. Fishing with heavy trawls and explosives damages the physical structure of reefs, as well as the coral animals that build them. Careless tourists and boat anchors also cause mechanical damage. Thermal pollution from power plants and global warming cause physiological stress that kills coral animals and leaves the reef structure vulnerable to erosion. Many of these impacts are the result of ignorance; people simply aren’t aware of the importance of coral reefs or the consequences of their actions, but the damage and threats to reefs continues to increase on a global scale.

Some of the most severe damage appears to be caused by thermal stress. Shallow-water reef-building corals live primarily in tropical latitudes (less than 30° north or south of the equator). These corals live near the upper limit of their thermal tolerance. Abnormally high temperatures result in thermal stress, and many corals respond by expelling the symbiotic algae (zooxanthellae) that live in the corals’ tissues. Since the zooxanthellae are responsible for most of the corals’ color, corals that have expelled their algal symbionts appear to be bleached. Because zooxanthellae provide a significant portion of the corals’ food and are involved with growth processes, expelling these symbionts can have significant impacts on the corals’ health. In some cases, corals are able to survive a “bleaching” event and eventually recover. When the level of environmental stress is high and sustained, however, the corals may die.

Prior to the 1980s, coral bleaching events were isolated and appeared to be the result of short-term events such as major storms, severe tidal exposures, sedimentation, pollution, or thermal shock. Over the past twenty years, though, these events have become more widespread, and many laboratory studies have shown a direct relationship between bleaching and water temperature stress. In general, coral bleaching events often occur in areas where the sea surface temperature is 1°C or more above the normal maximum temperature.

In 1998, the President of the United States established the Coral Reef Task Force (CRTF) to protect and conserve coral reefs. Activities of the CRTF include mapping and monitoring coral reefs in U.S. waters, funding research on coral reef degradation, and working with governments, scientific and environmental organizations, and business to reduce coral reef destruction and restore damaged coral reefs.

As co-chair of the CRTF, and as directed by the Coral Reef Conservation Act of 2000, NOAA has the responsibility to conserve coral reef ecosystems. NOAA’s coral reef conservation efforts are carried out primarily through its Coral Reef Conservation Program (CRCP). Under this program, NOAA works with scientific, private, government, and nongovernmental organizations at the local, federal, and international levels to address conservation actions. Among other actions, the CRCP undertakes a variety of mapping and monitoring activities to understand:

The first part of this lesson is intended to:

In the second part of this lesson, students design and prepare educational programs to improve public awareness of the importance of coral reefs and what needs to be done to reduce or eliminate harmful impacts from human activities. This activity offers many opportunities for cross-curricular activities, and may be extended over several weeks or months. If time is limited, you may choose to use the first part alone.


Learning Procedure

Part 1

1. Direct students to the Coral Tutorials at: You may want to assign different tutorial sections to each student group. Have each student or student group complete one version of the Corals Subject Review (downloadable), and lead a discussion to review the answers. Be sure that students understand the relationship between coral animals and their symbiotic algae (zooxanthellae), and that many corals under various types of stress will expel their zooxanthellae.

Briefly review the purpose and activities of the U. S. Coral Reef Task Force (CRTF) and the NOAA Coral Reef Conservation Program (CRCP), and highlight the monitoring functions that are intended to identify threatened reef areas and to improve understanding of reef ecosystems (visit for more information on the CRTF and for more information on the CRCP).

Tell students that a key CRCP activity is NOAA’s Coral Reef Watch Program which uses remote sensing and in-situ measurements for near real-time and long term monitoring, modeling and reporting of physical environmental conditions of coral reef ecosystems. The Coral Reef Watch Satellite Bleaching Alert System monitors sea surface temperatures at 24 selected reef sites around the globe.

“Coral bleaching HotSpots” are defined as sea surface temperatures that are greater than the normal maximum temperature. Some coral bleaching events have been noted in areas where the HotSpots are greater than 1 degree C. More often, coral bleaching results from thermal stress that accumulates over several days or weeks.

“Degree Heating Weeks” (DHWs) indicate the accumulation of thermal stress that coral reefs have experienced over the past 12 weeks. One DHW is equivalent to one week of sea surface temperatures one degree Celsius greater than the expected summertime maximum. Two DHWs are equivalent to two weeks at one degree above the expected summertime maximum OR one week of two degrees above the expected summertime maximum.

HotSpots and DHWs are used to define a series of “alert levels” for the 24 reef sites:

2. Briefly describe some of the satellites and sensors that currently provide various types of oceanographic data. A great deal of information on oceanographic conditions is available from various satellites. NOAA’s Polar Operational Environmental Satellite (POES) carries the Advanced Very High Resolution Radiometer (AVHRR), which provides information on sea surface temperature (SST) for the entire Earth on a daily basis. NASA’s Terra and Aqua satellites cross the equator in the morning and afternoon, providing coverage of the entire Earth surface every 1 – 2 days. These satellites carry Moderate Resolution Imaging Spectrometers (MODIS) that provide information on chlorophyll-a as well as SST. NASA’s QuikSCAT satellite carries the SeaWinds sensor that provides global information on wind speed and direction near the ocean surface. Data from these (and other) satellites are available free via the internet. Distribute copies of “Satellite Imagery Worksheet” to each student or student group. Tell students that their assignment is to use satellite data to answer the questions on the worksheet. When students have completed the worksheet, point out that the CRTF’s monitoring program keeps track of selected oceanographic conditions on an hourly or daily basis at twenty-four coral reef sites. You may want to have students visit to check out current conditions at these reefs.

Have students investigate the history of temperature conditions at each of the three reefs listed on the “Satellite Imagery Worksheet” over the period Jan 2001 to December 2007, using data at Ask whether temperatures have reached Alert Level 1 at any of these reefs during this time period. Students should recognize that this level has been reached at:

If you want to investigate the history of temperature conditions prior to December 2000, visit

3. Lead a discussion of how data from the CRCP monitoring program help protect coral reefs. Student will probably realize that these data cannot directly improve the condition of reefs, since the root problem appears to be climate conditions that are beyond human control (at least in the short term). These data are very useful, however, in identifying sites that are at risk of environmental stress so that scientists and resource managers can learn more about the response of corals and coral reef systems to these conditions. Ask students to discuss why coral reefs are at risk, and what they think can or should be done to reduce or eliminate the negative impacts of human activity on coral reefs. There is a strong possibility that a significant part of the current risk to coral reef systems is the result of human activity, particularly as it relates to global warming. Meaningful actions to address this type of issue depend upon widespread understanding of the problem and commitment to workable solutions. Public education is an important step toward building this sort of understanding and commitment. Have students brainstorm what “key messages” might form part of a public education program about coral reefs, what audiences should be targeted to receive these messages, and how these messages might be most effectively delivered to these audiences.

Part 2

Have students or student groups prepare one or more public education programs about coral reefs, based on the results of their brainstorming sessions in Step 3. Encourage students to consider various media, including publications, visual presentations, drama, music, etc. You may want to have an entire class work on a single program, or have smaller groups work on multiple programs using the medium (or media) of their choice. There are many possibilities, depending upon the target audiences. These presentations also offer cross-curricular opportunities, particularly with social studies, English language arts, and fine arts. Whatever media students choose to work with, their final presentation should be accompanied by a list of sources for the information they present. A good starting point for this activity is the Roadmap to Resources: Corals (, which provides links to many other sources of coral reef data and information.


The Bridge Connection

The Bridge is a growing collection online marine education resources. It provides educators with a convenient source of useful information on global, national, and regional marine science topics. Educators and scientists review sites selected for the Bridge to insure that they are accurate and current.

The “Me” Connection

Have students write a short essay on why coral reefs are personally important, what personal actions may contribute to human-caused threats to coral reefs, and what they could personally do to reduce these threats.


1. Have students or student groups prepare a report on a specific aspect of coral biology, ecology, or management. Some possible topics include:

See Roadmap to Resources: Corals ( for links to information on relevant topics.

2. Review and discuss “Things You Can Do to Protect Coral Reefs” at Even if you don’t live near a reef, you can help protect coral reefs in the U.S.A. and around the world.

3. For more lesson plans and activities related to coral reefs, visit the education web pages for NOAA’s Ocean Explorer Cayman Islands Twilight Zone 2007 Expedition at


Resources – National Ocean Service website’s Roadmap to Resources about corals, with links to many other sources of coral reef data, background information, and reports
Diamante-Fabunan, D. 2000. Coral Bleaching: the Whys, the Hows and What Next? OverSeas, The Online Magazine for Sustainable Seas. – “Coral Bleaching: Causes, consequences and response;” a collec­tion of papers from the ninth international coral reef sym­posium.
“The State of Deep Coral Ecosystems of the United States,” 2007 report from NOAA providing new insight into the complex and biologically rich habitats found in deeper waters off the U.S. and elsewhere around the world.,0,7842752.special – “Altered Oceans,” five-part series from the Los Angeles Times on the condition of Earth’s ocean; published July 30 – August 3, 2006 – description and links to satellite remote sensing ocean data provided by NOAA CoastWatch – search page for satellite remote sensing ocean data provided by NOAA CoastWatch; use navigation bar at left to select geographic region, type of data, and date range – NOAA’s Coral Health and Monitoring Program home page, with links to coral reef data, maps, and other resources – coral bleaching hotspot chart - Tropical Ocean Coral Bleaching Indices for 24 coral reef sites

Hughes, T.P., et al. 2003. Climate Change, Human Impacts, and the Resilience of Coral Reefs. Science 301:929-933. Available online at

National Science Education Standards

Content Standard A: Science as Inquiry

Content Standard C: Life Science

Content Standard D: Earth and Space Science

Content Standard E: Science and Technology

Content Standard F: Science in Personal and Social Perspectives


Ocean Literacy Essential Principles and Fundamental Concepts

Essential Principle 1. The Earth has one big ocean with many features.

Essential Principle 6. The ocean and humans are inextricably interconnected.

Essential Principle 7. The ocean is largely unexplored.



Keeping Watch On Coral Reefs

Student Worksheet

Two conditions that have been linked to coral bleaching are water temperatures that exceed 30°C and little or no surface wind. Your assignment is to use satellite data to investigate whether these conditions have occurred during the past week at three coral reef areas. These reefs are:

I. Follow these steps to obtain the necessary information about sea surface temperatures (SST):

1. Go to

2. Build your Query:

  1. In the “View Results as” window, select “As Images”

  2. In the “Select a Region” window, select “Caribbean” or “Gulf of Mexico”

  3. In the “Select Product” window, select “Sea Surface Temperature”

  4. In the Sensor Select window, select all of the options

  5. In the Satellite window, select all of the options (NOTE: Select all of the options for sensors and satellites because you may not be sure which systems are operating during the dates of interest. This search will retrieve all available images for the dates you specify, so you can select the ones that are most useful.)

  6. In the From and To date windows, enter the dates that correspond to the past week.

3. Click on “Search”

4. Select imagery for each of the three reefs, and determine the sea surface temperature (SST). 

II. Follow these steps to obtain the necessary information about surface winds data

1. Go to
2. Build your Query:

  1. In the “View Results as” window, select “As Images”

  2. In the “Select a Region” window, select “Caribbean” or “Gulf of Mexico”

  3. In the “Select Product” window, select “Surface Winds”

  4. In the Sensor Select window, select all of the options

  5. In the Satellite window, select all of the options

  6. In the From and To date windows, enter the dates enter the dates that correspond to the past week.

3. Click on “Search”

4. Select imagery for each of the three reefs, and determine the surface winds.