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Coral Watch Coral Bleaching Survey Activity Guide

Welcome Citizen Scientists!

Rising water temperatures as well as ocean acidification are a major contributor to  coral bleaching events. Get involved in our Coral Watch Activity to monitor and protect coral reefs using our Virtual Reef. To learn more about global warming and coral bleaching please read our article in the ReefQuest knowledge base. With the Coral Watch survey and the ReefQuest Virtual Reef you can collect data as scientists would in the field, then learn to interpret the data and combine it with the data of other citizen scientists around the world. 

This Activity Guide is designed to be used by both teachers/educators and students. Throughout the activity certain section will be labeled ADVANCED and they are generally written for teachers or educators to gain greater depth of understanding. Students in 10-12 grade could read these sections if they wish to go in greater.  Sections of this module identified as PREPARATION  should be done prior to engaging in the activity. Sections identified as BACKGROUND are knowledge necessary to understand the activity, and should be read by prior to undertaking the activity. STEPS are actions to be taken to actually perform this activity. 


PREPARATION What will you need in for this activity?

  1. Access to the internet with the ability to view the ReefQuest Virtual Reef. This may require a browser plug-in to be automatically installed the first time, (Silverlight from Microsoft). If you are prompted to allow its installation, please do so. Verify that each computer you will be using is working correctly with the Virtual Reef, and has the plug-in installed by accessing the Virtual Reef at least once and navigating around any of the transects. Your computer(s) should also have the latest updates to the browser and operating system. The Virtual Reef has been tested with both Windows (XP or later) and Macintosh (Os X or later). The Virtual Reef does not yet work with mobile devices such as iPAD or iPHONE or ANDROID-based tablets. The Virtual Reef will work with Internet Explorer, Mozilla Firefox and Safari browsers. We have not yet tested the support of the Virtual Reef with the Chrome browser.
  2. Print out a sufficient number of ReefQuest CoralWatch Data Sheet.
  3. If you will be using a hard copy of the Coral Watch card, print out a sufficient quantity of the cards using an inkjet  photo printer on photo paper. Be aware that the card will print on a 8 1/2 x 11 inch sheet, so you need a sufficient number of sheets available. Cut the resulting cards to size per instructions. Note that options exist in this activity to use the card as a floating online window instead of printing it. If you chose this method you do not need to print the cards, but be sure to read and understand how to use the card on a floating window, as described later in this article. 
  4. Print the coral type identification card, in sufficient quantities for each participant in the survey. Ideally this should be printed in color. You might want to consider using that identification card to practice identifying corals using the virtual reef prior to undertaking this activity. A ReefQuest virtual survey that offers you the ability to practice utilizing this card to identify coral types is available from ReefQuest as the Coral Types survey. You might want to consider doing that survey first. 


National Education Science Standards

This activity is aligned to these National Science Education Standards. This activity is designed to be spiraling, targeted to 10-11-12 grades, however, educators can teach aspects of this activity in 8-9 grades if they interpret the background materials for their students. 


BACKGROUND What is CoralWatch? 

Coral Watch is an organization built on a research project at the University of Queensland in Brisbane, Australia. Coral Watch uses the Coral Health Chart as a simple, non-invasive method for the monitoring of coral bleaching, and assessment of coral health. The accuracy and efficacy of the CoralWatch protocol was extensively published in scientific journals like Coral Reefs. In the field underwater, users simply compare colors of corals with colors on the chart and record matching codes. ReefQuest has adopted this protocol for use with our Virtual Reef.

There are, however a few differences if you use theCoralWatch protocol with the Virtual Reef online: first of all, for the ReefQuest Virtual Reef we have created a Modified Coral Watch Coral Health Chart, which utilizes a coral type classification that has been adapted for Hawaiian coral types. Coral in Hawaii is different from any other parts of the world, with unique  types.  


BACKGROUND What is coral bleaching?

Coral bleaching is the whitening of coral due to a loss of symbiotic algae living within the coral tissue. In healthy coral, algae supplies energy and provides color. During bleaching events, coral expels the algae from their tissue which changes the colour of the coral. As coral expels more algae the coral becomes lighter in color.

Bleaching events in Hawaii have not been as severe as those in other parts of the world, such as on the Great Barrier Reef in Australia. However, it is important to measure color intensity as baselines so that reefs can be monitored for trends.

Since the virtual reef will allow you to access reef conditions over time, you have the opportunity to measure and observe these baselines over time. CoralWatch allows the creation of profiles of color distribution that can be studied from year to year for trends and changes. This data becomes part of the "reef fingerprint" that is a quantitative indicator of the overall coral reef health. 


BACKGROUND What are the objectives of this Activity?

You can join others in collecting data from random sections of the ReefQuest Virtual Reef about the color intensity (and hue) of random coral colonies:

  • so that a color score can be generated as an indicator of the reef's coral health.
  • a quantitative baseline can be established to study its trend over time.
  • a comparison can be made with reference "healthy" reefs.
  • data can be collected so that the conditions of the reef at the present time can be documented for future study.
  • a quantitative measure of coral bleaching can be established on this reef.


ADVANCED Is it real data? 

The ReefQuest Virtual Reef is a digital replica of real coral reefs that utilizes special 3D panoramic technology to allow you to view it in great detail. Our team has pre-processed each image to carefully effect color calibration under natural light, utilizing special camera and light equipment underwater. The result is a highly detailed, realistic image of the real coral reef, with color approximating the true color under natural sun light.

Color and color perception, as well as lighting underwater are, however, very complex topics and no computer image can be an absolute identical match to reality. This is further complicated by the inherent differences among various computer monitors, video cards and background lighting conditions, which all contribute to differences in color perception and reproduction on-screen. Just think of what happens when you go to a television store and  see the same picture side by side across many types of television monitors. It can vary considerably.

For this reason we do not mix data collected off the ReefQuest Virtual Reef with data collected underwater in the field at the real reef site. So does this mean that the data you collect on the virtual reef is for educational purposes only and is not a valid scientific measure?

The answer hinges on two factors that are part of the survey methodology:  

  • First, because each image in the virtual reef was captured with consistent lighting and special color matching technology, the result is very consistent from image to image. This means that, on any one monitor, the virtual reef might be slightly darker or lighter, or shifted to one color or another, compared with real life, but these color shifts will be consistent throughout the virtual reef (at least as long as you use the same computer and monitor). That consistency means that the color measurements you create are going to be consistent with each other, and any trend data you derive from them is likely to be reasonably accurate.
  • Second, CoralWatch accuracy increases with the greater number of data points and,  errors such as those introduced by lighting or color difference,  diminish with the larger number of data points. This means that when you combine your data with other data collected from other citizen scientists, the error introduced by color shifts on any one monitor gets progressively less significant with the growing number of data points. IN quantitative measurements we have proven that and the data eventually converges to something that approximates very closely the data collected in the field, i.e. reality.

For this reason, as long as the data is consistently collected on the Virtual Reef, (not mixed with data collected in the field), the resulting analytics, especially trend data, are a close approximation to the data measured in the field. For this reason the data you collect on this web site is a good approximation of the real reef condition as of the date of the imaging of the Virtual Reef.

This however can not be a substitute to data collected in the field, and an approximation of reality, however accurate,  can not be substituted for scientific data collected in the field. For this reason,  the data collected from the Virtual Reef is fundamentally an educational experience and we do not use it for scientific research, nor do we submit the data to the Coral Watch survey portal maintained by the University of Queensland. We do collect data in the field, using the regular Coral Watch card and do contribute that data to the real survey.  You can compare the Coral Watch scores being collected in the field as published by the University of Queensland with those in our our Virtual Reef Analytics page to see how the Virtual Reef and the real reefs compare. 


BACKGROUND Why do corals change color? 

In healthy coral, algae (symbiotic dinoflagellates) live within the coral tissue. Algae provide the coral with energy (sugars and amino acids) and give the corals their characteristic colour. 

Stressful environmental conditions can cause the coral to expel the algae, changing coral colour from brown to white, purple or green. This whitening of coral is called ‘coral bleaching’. Sometimes corals can recover from bleaching. If the stressful conditions are severe or persist for a long time, loss of algae and the nutrients they provide for coral can lead to coral death. Even when corals do recover, they do not always return to full health.

The mass bleaching event of 1998 is the most severe bleaching event on record, where one-sixth of the world’s coral colonies died! Every year, many coral reefs around the world show signs of coral bleaching. 

Many environmental stressors can lead to bleaching. However, research shows that increased water temperatures due to global warming is the major cause of recent mass bleaching events. Sea temperatures are predicted to continue to rise, and thus bleaching is expected to occur more frequently.  


BACKGROUND Coral Watch Color scores and the Coral Watch Coral Health Card

The color charts are based on the actual colors of bleached and healthy corals. Each color square on the chart corresponds to the concentration of symbiotic algae which lives in the coral tissue which is directly linked to coral health. University of Queensland determined this through extensive measurements. They also discovered that the color hue of the coral is less important than the color density. When taking measurements both the lightest and darkest scores for each sample are recorded to allow for natural colour variation across the coral. We use the average score of each sample for analysis. 

Before undertaking the CoralWatch card you need to obtain a CoralWatch Coral Health Card. 


As discussed above we have modified the card to reflect coral types more commonly found in Hawaii, which is where the virtual reef is located. 



ADVANCED Does this mean that you can not use the original card from CoralWatch? You can absolutely use the original card, but you need to translate the coral types identified in the original card.


A simple equivalency is used by ReefQuest between the coral type classifications used in Australia on the original Coral Watch card and our ReefQuest modified classifications:


Original CoralWatch                 Modified CoralWatch

Boulder Type                =            Smooth

Branching Type             =            Branching

Plate Type                    =            Rice

Soft Type                      =            Other


 Contact us to discuss this translation if you have any questions or, if you have an original CoralWatch card.


PREPARATION You have 3 ways to get the Modified Coral Watch Card:

  1. You can download one here. It is important that if you are going to print it, you realize that you are introducing an additional source of error, as each printer will have variable color fidelity. If you chose to print it, you should generally print it on glossy photo-paper using an ink-jet photo printer. We have created special color profiles for most photo printers that are embedded in the file, and should give you a reasonable color match. Once you print the card you should cut it so that the edges of the paper are at the color bars on each side. Note that you also have a coral type classification quick guide for you reference with the printed card.
  2. You can request an original Coral Watch card from us, who will provide it to you courtesy of the University of Queensland. This should be the method if you think you will use the card in the water on a real reef in addition to using it on the virtual reef
  3. You can display one on-screen and use it as a floating card over the virtual reef images. The advantages of this method are that any color shifts introduced by your monitor, will affect in the same way the Coral Watch Card and the Virtual Reef. This actually results in a more accurate relative result when you profile the samples. If you choose this method make sure you have thought through how you are going to layout the various windows on your screen, between the virtual reef, the data entry and the Coral Watch card. 


BACKGROUND Coral types

Classifying corals at the species level is very difficult, so easily identified groups are often used when recording data about coral cover or general coral health. For this purpose, coral types are described simply by the basic growth forms or shapes of coral colonies.

The Modified Coral Health Chart uses four coral types to classify corals. This simplified classification was developed to support the Eyes of the Reef survey in Hawaii. 

  • Branching refers to any branching coral such as Pocillopora species. 
  • Smooth refers to any massive or rounded corals such as the Porites species. 
  • Rice refers to Montipora species, and the Other category includes rare corals such as  corals lacking a hard skeleton (soft). 

PREPARATION For a simple visual identification card, suitable for lamination for use underwater as well as in the virtual reef, click here. This identification card was created by the Eyes of the Reef program. You should print this card and have it available before  undertaking the Activity. 

Corals can exist in many shapes, and some corals may not clearly match any of these categories. Our aim is to keep the chart and survey as simple as possible, so if you’re experiencing difficulties when classifying your corals, please simply choose the closest coral type.



PREPARATION How to use the Coral Watch chart

For each specimen of coral (coral colony) select the lightest section and match it to a hue (B-C-D-E) and an intensity (1-6). The hues represent common coral colors; they just make it easy for our eyes to make an accurate match. The brightness of the colors ranging from 1 to 6 are the same on every side. Enter that information in the Coral Watch Data Sheet. Repeat the process on the SAME sample by matching hue and color in the darkest section of the specimen. By collecting both the lightest and darkest we average out differences that are normally present in coral colonies. So for each specimen you need a set of lightest and darkest hue-intensity matches. DO NOT take measurements on dead coral (clue: no polyps present). Also when measuring branching coral, DO NOT measure the tips of the branches, as those normally appear white. These are areas where the coral is growing and their color is unrelated to any bleaching. 

Finally you will discover that colors in the coral is not always a perfect match. There may also be colors that are not on the scale. Just as for coral types, pick the closest color, and remember that the quality of your survey improves with the number of data points, so there is tolerance in the method for approximation. 

Certain corals found in Hawaii will have a hue tending to the blue. For those coral use the approximate green (B) scale and focus on the intensity (1-6) which studies have shown is the important measurement in creating the color score. Additionally some corals such as Hydrocorals are not measurable with CoralWatch chart. This includes purple corals. Simply exclude them from your survey, as those corals are typically not subject to bleaching. 


PREPARATION Survey Methods

Make certain you know how to use the virtual reef and understand how to navigate it and what a transect is. You can choose one of three survey methods depending upon your skills, experience and location:

  • Random Survey – select corals randomly, such as choosing the coral closest  to you every second "mouse"click while navigating the virtual reef. Make sure your selection is truly random.
  • Quadrant or Transect Survey – select your corals by finding a square area (a quadrant = a scene in the virtual reef)  or following a line (transect). Then assess the corals within the quadrant or on the transect line.
  • Easily Identified Corals – select corals that you can easily identify and return to as new years of the Virtual Reef are published (2012 will be coming soon!). 


STEPS How to use the Coral Health Chart with the ReefQuest Virtual Reef


  1. Become familiar on the use and navigation of the Virtual Reef. Use the Virtual Reef Tutorial to learn how to navigate the virtual reef. Learn how to expand your view to full screen, and organize the screens for optimal viewing and organization. See an example from this screen shot. 
  2. Choose a random coral in any of the transects in the Virtual Reef. Use the Coral Watch Data Sheet to collect the data. Write in the worksheet the transect code name. You can also use the "highlights" pre-defined in most transects to navigate around sections of the transect.
  3. Zoom close to coral of interest and select the lightest area, avoiding the tip of branching corals. Do not zoom so close that you are seeing individual polyps. At that magnification it becomes harder to assess color hue. 
  4. Hold the colour chart next to the selected area. If you are using the display coral chart in the floating window, move that window close to the are you are observing. 
  5. Find the closest color match.
  6. Record the matching color code along with coral type on the data sheet.
  7. Repeat steps 2 to 5 for the darkest area of the coral.
  8. Continue survey with other corals.
  9. When you finish, go to our Virtual Survey menu, and navigate to the the Coral Watch Survey menu. This is the data entry module that allows your data to be entered into our database for processing.  Read the instructions and then scroll to the bottom to access the online form to enter your data. It is simple and fast to input the data you collected in the Coral Watch Data Sheet using our online form. If you don’t have access to the web you can send us your data sheets and we will enter them on your behalf. See our mailing address here.  Thank you for being a citizen scientist and adding your data to that of other citizen scientists. As you know the more data points the better our analysis of the virtual reef will be. Your data will be analyzed and part of the data being visualized on our site approximately 60 minutes after you submit it. 


  • Assess at least 20 corals per survey (the more the better)
  • Get close enough by zooming and panning so that you can see clearly the coral specimen you are measuring, but not so close that you are seeing individual polyps. 
  • Don’t forget to record the transect name, as you will need that when entering data in the Virtual Survey name.
  • Avoid areas that exhibit disease or algae cover. Colors might be affected by coral disease. There are other surveys that focus on coral disease. 


BACKGROUND What does it all mean?

The numerical values on the chart are analyzed to determine the health index values. The higher the number the darker the coral and the more symbiotic dinoflagellates are contained in the coral tissue.Bleached corals have low numbers of symbionts, are light in color and have low color score values. Even if the reef is healthy not all corals will have the same number of symbionts, or the same color, and it is expected that you will find a distribution of color scores spanning the entire range. It is the shape of the distribution that can be used to determine the condition of the reef under investigation.


What a graph will look like for a healthy reef?

A healthy reef would be expected to have a very small number of corals with a color score of 1, few at 2 and larger numbers with higher color scores. The distribution of coral color scores for three different healthy reefs in Australia's Great Barrier Reef (Heron Island, Green Island, Lizard Island) is shown below.


A healthy reef will typically have a distribution of colors that is shaped like a bell curve, with the majority of the corals scoring in the middle of the scale, or around 3.








What a graph for a bleached reef will look like?

A bleached reef would be expected to have a large number of corals with a color score of 1 and very few corals with values of 5 or more. The figure below shows the score for Heron Island in the Great Barrier Reef in Australia at the height of a bleaching event (light columns) and then later after a recovery (dark columns). During the bleaching event, over 60% of measured corals (total of 110 corals measured) have a color score of 1, indicating that most of the reef had lost most of their symbionts during that time. Four months later the distribution looks completely different, only 15% of the measured corals have a color score of 2 or less, and the reef had recovered. 


STEPS Evaluation of the Virtual Reef

You can visualize the conditions of the Virtual Reef by using ReefQuest's visualization page. Each result is plotted in real time. Here are some quick links to the most important results:


Visualize in real time the Virtual Reef's:

Coral Color Score by Coral Type.  This is the average color score and provides a quick assessment of the health of the reef. The higher is the score, the healthier is the reef.

Coral Color Score Distribution by Coral Type.  This is the distribution of coral color scores for the virtual reef, similar to the curves discussed above. 

Summary of Coral Colors. This is the percent frequency for each one of the color groups in the Coral Watch card (B-E). This gives you an assessment of the overall color of the virtual reef.

Percent of Coral Types Surveyed. This is a pie chart that shows you the relative precent of each coral type in the survey. It represents a reef census. 


Compare the data in the virtual reef analysis page with the diagrams above, showing you healthy and bleaching reefs. What conclusions can you draw from that comparison? You can post your conclusions as a comment to this activity. HINT: Compare the shape of the distribution. Does it look like a bell curve or something else? Are your conclusions different if you only consider one type of coral? Does it appear that one coral type might be more susceptible to bleaching than others? 


Conduct your own evaluation of the Virtual Reef based on your own data.

You can analyze just data you collect by using the ReefQuest ReefQuest Coral Watch Reef Fingerprint Worksheet. This is an Excel spreadsheet which uses the same statistical analysis used in our survey to produce graphs similar to those discussed above for just your own data. Use it to enter just your own data and compare your own data with the data above. Are there differences? What do you suppose those difference come from?  You can use this spreadsheet to also create your own charts for a poster presentation on your work. 


ADVANCED Taking it one step further ...

Compare the Virtual Reef with data collected by our teams on the Real Kahekili Reef

Our teams are collecting data using the CoralWatch card in the field on the Kahekili Reef, on the island of Maui. You can compare your data as well as the data in the virtual reef with the data our team collected for 2011 in the field, at the same time as when the 2011 virtual reef was imaged. Do the results match? If not why do you suppose not? Use the comment fields at the end of this module to share your conclusions. 



Average color score over time

This line graph shows all monitoring dates with average health scores for a reef in the Great Barrier Reef in Australia. Each data point is the average of all the colour scores for that time period (month, year, etc.), from all the data collected so far. This shows how the health of your reef is progressing over time. Significant drops in your colour score can relate to threats to the reef such as bleaching, diseases, invasive species or increased tourism. From this graph, scientists would likely have looked into what naturally took place around June 2008 in this area, as well as what humans were doing, to try and figure out why such a big dip in health occurred. Although it makes for a boring graph, we want to see a high, fairly straight line across time, which means that the reef’s health is not changing much. Of course, lines that are moving upwards are even better!

As new updates  are added to the Virtual Reef, create your own diagram of the trends on the virtual reef over time. Is it flat? Does it trend lower or higher? What would that mean? 

Discuss these questions in the comments field below. 





ADVANCED Further reading & Bibliography

  1. Siebeck, Marshall, Kluter, Hoegh-Guldbergm Monitoring coral bleachi...
  2. Siebeck, Logan, Marshall, CoralWatch - a flexible coral bleaching m...
  3. Climate Change and Coral Reefs, CGCRMN 2010





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