Product and Future:

The intent of this product was to derive a quality-controlled (QCed) bleaching observations dataset that was matched to various satellite spatial scales for the sole purpose of validating satellite algorithms that aim to predict aspects of coral bleaching.

Please note that this is the first version of the QCed bleaching observations database. Initial discussions about this product with a number Coral Reef Watch (CRW) users and stakeholders has resulted in our decision to evolve this into a more generic product with broader aims. As a result, CRW will continue developing and evolving this product to suit a range of uses rather than just satellites. Ideas for improvements that are already under consideration include:

1. Implement Pathfinder Version 5.2 to extend the years of the bleaching observations beyond 2009. Validation of the use of Pathfinder 5.2 for accurate production of coral thermal stress indices is underway.
2. Development of a quality control for reports of no bleaching.
3. Inclusion of databases held by other NOAA divisions and external agencies.
4. Including quality flags for each step in the quality control methodology so that users can choose which tests they wish to include. In other words, all data will be retained and users will be able to choose which quality control (QC) tests to use on the complete dataset. If there is sufficient demand, we will consider developing a web-based GUI so that users can choose which QC tests to implement. The result will be a downloadable bleaching database with the user's personalized QC test.

For the initial version of this product however, QC of the coral bleaching observations data was conducted with satellites in mind; therefore, output is only tailored towards validating satellite thermal stress products such as CRW's Degree Heating Weeks (DHW) and Light Stress Damage (LSD) products (see http://coralreefwatch.noaa.gov/satellite/index.php).

Purpose:

One of the main aims of NOAA Coral Reef Watch (CRW)'s decision support system for coral bleaching thermal stress monitoring is to provide managers and scientists with information about the onset, severity, and duration of bleaching thermal stress that could cause mass coral bleaching, and resulting mortality. To quantify the ability of a satellite product to provide useful information about a coral bleaching event, it is important to have a QCed validation/calibration dataset of in situ bleaching observations. The purpose of the Quality-Controlled Coral Bleaching Observations product presented here is to provide data for calibration and validation of CRW's satellite-based thermal stress products.

Many organizations and individuals collect coral bleaching information and data from their local reefs. One of the more well-known, global, public datasets is ReefBase, administered by WorldFish. Because of its geographic coverage and popularity, CRW decided to start populating its Quality-Controlled Coral Bleaching Observations database using ReefBase data.

The bleaching observations data that populate ReefBase are provided voluntarily by interested persons, regardless of their qualifications of experience; the result is a database with varying quality. For this reason, CRW has developed a quality control methodology to filter the original ReefBase data and produce a quality bleaching observations dataset tuned specifically for validating CRW satellite products.

Methodology:

The below methodology was developed and run separately at 0.044 degree (approx. 4 km), 0.1 degree (approx. 11 km), and 0.5 degree (approx. 50 km) resolution to form three separate datasets tuned to the three different spatial resolutions. These datasets at 4, 11, and 50 km resolution that comprise the Quality-Controlled Coral Bleaching Observations product should be viewed independently of one another, not comparatively. Data were passed through a number of QC checks. Only those reports that passed each step were retained in the final database presented here. Although many of these quality control steps can be performed in any order, the QC steps (in order of use for this version of the QC methodology) are as follows:

1. All ReefBase reports have a date associated with them; however, some only have a year and no month recorded. In this first step, all records without a month in their date stamp were discarded.
2. Since this particular QCed dataset is aimed at obtaining bleaching data only, all reports that were marked as having "no bleaching" (i.e., zero bleaching observed) were discarded. Although "no bleaching" reports are very important for a complete understanding of the relationship between stress and bleaching, a different methodology is needed for analyzing and QC-ing "no bleaching" reports. This will be one of the next steps in the future development of this product.
3. All ReefBase reports include a latitude and longitude associated with the report reef. For each quality control resolution (4, 11 and 50 km) all pixels containing reefs were determined using a UNESCO-derived 1 km map of global reef locations (also available from ReefBase). At each resolution, the report latitude and longitude were compared to the location of reefs. If the report did not lie within a reef pixel, it was discarded. Future versions of this product will incorporate the use of the Millennium Coral Reef Map.
4. The temporal scale of a thermal bleaching event is on the order of a number of weeks to months; the temporal scale of most of the ReefBase datasets is also monthly. As a result, if multiple reports occurred within the same pixel of a given spatial resolution (4, 11, or 50 km) in the same month, they were treated as a single report.
5. Reports that lie within a reef pixel that didn't experience thermal stress for that year were also discarded to distinguish thermal bleaching events from non-thermal bleaching events.

It is quite important to attempt to ensure that each bleaching observation report is related to thermal stress and not bleaching caused by non-thermal stress. Test (5) above helps in this determination but does not complete the steps needed to ensure the in situ bleaching observation corresponds to a thermal bleaching event. It is still possible for a thermal stress event to occur in a year where coral bleaching was caused by non-thermal stress. Linking the timing of an in situ bleaching observation with a thermal event is one way to improve the likelihood of the bleaching being triggered by thermal stress. However, since NOAA CRW seeks to use the in situ bleaching observation data to validate satellite thermal anomaly products that aim to provide information about bleaching, it is important not to pre-empt the relationship between temperature and bleaching, even though the scientific literature is in no doubt that a strong relationship exists. To this end, we have provided, as part of the three ASCII files above (at 4, 11, and 50 km resolutons), twelve monthly measures of thermal stress with each QCed bleaching observation from ReefBase. This should help the user decide for him/herself when a thermal event began, peaked, and abated, and whether or not the associated QCed bleaching observation was related to a thermal stress event.

Since each of the three resolution datasets are designed to be used independently of each other, it was only necessary to derive a measure of monthly thermal stress comparable within each of the three resolutions, rather than between each of these datasets. Determination of monthly thermal stress was therefore chosen to suit the available sea surface temperature (SST) data at each of the three resolutions. Methodologies used for each of the three resolution datasets are as follows:

AVHRR Pathfinder 5.1 was used as the basis for all SSTs, providing a dataset spanning 1983-2009. In keeping with the methodology of the current CRW 0.5 degree resolution operational SST product, a 50 km dataset was derived using the hottest 2x2 pixels in each 0.5 degree grid cell. From this, a hindcast DHW product was produced using the CRW 0.5 degree operational DHW product methodology, and the maximum SST value for each month was used to derive the monthly dataset.

A monthly 11 km SST dataset was derived using an average of the 4 km pixels within each grid cell. A degree heating month (DHM) value was then determined for each month in each pixel (after Donner et al., Global assessment of coral bleaching and required rates of adaptation under climate change. Global Change Biology, 11, 1-15, 2005). This is a very similar metric to the DHW product, only it is calculated monthly using monthly SST values with the MMM as the trigger, rather than MMM+1°C.

Lastly, a 4 km dataset was derived by averaging all clear pixels in each month. Once again, a DHM value was determined for use in the QC.

For all three SST calculations of monthly thermal stress, the climatology followed the current 50 km DHW operational methodology by only using SSTs in 1985, 86, 87, 88, 89, 90 and 93 (see the description of CRW's operational climatology for details).

Data File Description:

The output from the Quality-Controlled Coral Bleaching Observations product consists of three ASCII files. Each row within a file is one bleaching observation report; therefore, the total number of rows within a file equates to the total number of QCed bleaching observations, with the top row consisting of column headings. Column descriptions are as follows (note that the first four values refer to each QCed bleaching observation report from ReefBase, and the next 13 values help the user to understand the thermal stress history of that pixel in the year the coral bleaching was actually recorded:

1. Latitude of record (lat)
2. Longitude of record (lon)
3. Year of record (year)
4. Month of record (mth)
5. Value of maximum thermal stress value (maxStr)
6. Thermal stress value for January (Jan)
7. Thermal stress value for February (Feb)
8. Thermal stress value for March (Mar)
9. Thermal stress value for April (Apr)
10. Thermal stress value for May (May)
11. Thermal stress value for June (Jun)
12. Thermal stress value for July (Jul)
13. Thermal stress value for August (Aug)
14. Thermal stress value for September (Sep)
15. Thermal stress value for October (Oct)
16. Thermal stress value for November (Nov)
17. Thermal stress value for December (Dec)

Please note that the thermal stress values were derived to assist in deciding if the bleaching recorded was related to thermal stress or if the bleaching was caused by a non-thermal stress such as water quality. To this end, the user should not dwell on the value of the thermal stress, other than to ask the questions: 1) Was there any stress (i.e., is the stress value greater than zero?); and 2) If there was a stress event, in which month(s) did it occur, and in which month did it peak?

Contact Us:

If users and other interested parties wish to contribute to future development of this product, please email CRW at coralreefwatch@noaa.gov.Given that we will be developing the Quality-Controlled Coral Bleaching Observations product for other users, including non-satellite users, we are interested to form partnerships to obtain bleaching or no bleaching observation data and to hear users's suggestions for future directions.