Degree Heating Weeks Research Articles

Validation of degree heating weeks as a coral bleaching index in the northwestern Pacific

Mass bleaching is the most significant threat to coral reefs. The United States National Oceanic and Atmospheric Administration monitors world sea surface temperature (SST) and releases warnings for bleaching based on degree heating weeks (DHW), which is the accumulation of temperature anomalies exceeding the monthly maximum mean SST for a given region. DHW values >4.0 °C-weeks are thought to induce bleaching, and those >8.0 °C-weeks are thought to result in widespread bleaching and some mortality. This study validates the effectiveness of DHW as a mass bleaching index by on-site historical observation at eight sites in the northwestern Pacific Ocean. The mass bleaching events occurred during different years at different sites. The recorded years of the bleaching events matched well with DHW values >8 °C-weeks, and the logistically projected probability of bleaching against DHW showed a positive relationship. DHW provides a reasonable threshold for bleaching.

Temporal patterns of coral cover in the offshore Pilbara, Western Australia

Patterns of hard coral cover and benthic composition were assessed at seven sites around Barrow Island in the Pilbara region of Western Australia between 2008 and 2013. While the per cent hard coral cover around Barrow Island was relatively stable between 2009 and 2012, there was a 69.3 % proportional change in hard coral cover between 2012 and 2013. Concomitant with this decline, Principle Coordinates Analysis showed a shift towards turf/coralline algae and there was a reduction in the proportion of the Acroporidae and a relative increase in the proportion of the Poritidae at most sites. During early 2013, sea surface temperatures around Barrow Island rose above seasonal averages, reaching 7.4 °C-weeks (degree heating weeks) from late February 2013 to mid-April 2013, and the decline in hard coral cover and shifts in benthic composition appear to be related to mortality associated with a coral bleaching event in early 2013.

Skeletal records of community-level bleaching in Porites corals from Palau

Tropical Pacific sea surface temperature is projected to rise an additional 2–3 °C by the end of this century, driving an increase in the frequency and intensity of coral bleaching. With significant global coral reef cover already lost due to bleaching-induced mortality, efforts are underway to identify thermally tolerant coral communities that might survive projected warming. Massive, long-lived corals accrete skeletal bands of anomalously high density in response to episodes of thermal stress. These “stress bands” are potentially valuable proxies for thermal tolerance, but to date their application to questions of community bleaching history has been limited. Ecological surveys recorded bleaching of coral communities across the Palau archipelago during the 1998 and 2010 warm events. Between 2011 and 2015, we extracted skeletal cores from living Porites colonies at 10 sites spanning barrier reef and lagoon environments and quantified the proportion of stress bands present in each population during bleaching years. Across Palau, the prevalence of stress bands tracked the severity of thermal stress, with more stress bands occurring in 1998 (degree heating weeks = 13.57 °C-week) than during the less severe 2010 event (degree heating weeks = 4.86 °C-week). Stress band prevalence also varied by reef type, as more corals on the exposed barrier reef formed stress bands than did corals from sheltered lagoon environments. Comparison of Porites stress band prevalence with bleaching survey data revealed a strong correlation between percent community bleaching and the proportion of colonies with stress bands in each year. Conversely, annual calcification rates did not decline consistently during bleaching years nor did annually resolved calcification histories always track interannual variability in temperature. Our data suggest that stress bands in massive corals contain valuable information about spatial and temporal trends in coral reef bleaching and can aid in conservation efforts to identify temperature-tolerant coral reef communities.

Massive hard coral loss after a severe bleaching event in 2010 at Los Roques, Venezuela

<span>Durante las últimas décadas las anomalías térmicas han sido más frecuentes y severas en el Caribe, quedando pocos arrecifes exentos de eventos masivos de blanqueamiento (EMB). En el Parque Nacional Los Roques, Venezuela, un archipiélago poco afectado previamente por EMB, la temperatura del agua a 5m de profundidad alcanzó 30,85°C en septiembre 2010, y fue >29,0°C entre mediados de agosto y la primera semana de noviembre en cuatro arrecifes. El 72% de 563 colonias de escleractinios estaban blanqueadas o pálidas para octubre de 2010, mientras que para febrero 2011, el 46% de las colonias aún estaban afectadas. Para febrero 2011, la cobertura béntica coralina promedio disminuyó de 45 a 31%. Además, los arrecifes mostraron una alta prevalencia (de hasta 16%) de enfermedad de banda negra en Octubre 2010, y de plaga blanca (11%) en Febrero 2011. Como consecuencia, es probable que la mortalidad coralina resulte mayor a la reportada acá. Sin embargo, Los Roques es poco afectado por perturbaciones antropogénicas y cuenta con un alto reclutamiento de corales, lo cual podría contribuir a su recuperación.</span>

Reef-Scale Thermal Stress Monitoring of Coral Ecosystems: New 5-km Global Products from NOAA Coral Reef Watch

The U.S. National Oceanic and Atmospheric Administration (NOAA) Coral Reef Watch (CRW) program has developed a daily global 5-km product suite based on satellite observations to monitor thermal stress on coral reefs. These products fulfill requests from coral reef managers and researchers for higher resolution products by taking advantage of new satellites, sensors and algorithms. Improvements of the 5-km products over CRW’s heritage global 50-km products are derived from: (1) the higher resolution and greater data density of NOAA’s next-generation operational daily global 5-km geo-polar blended sea surface temperature (SST) analysis; and (2) implementation of a new SST climatology derived from the Pathfinder SST climate data record. The new products increase near-shore coverage and now allow direct monitoring of 95% of coral reefs and significantly reduce data gaps caused by cloud cover. The 5-km product suite includes SST Anomaly, Coral Bleaching HotSpots, Degree Heating Weeks and Bleaching Alert Area, matching existing CRW products. When compared with the 50-km products and in situ bleaching observations for 2013–2014, the 5-km products identified known thermal stress events and matched bleaching observations. These near reef-scale products significantly advance the ability of coral reef researchers and managers to monitor coral thermal stress in near-real-time.

Forecasting decadal changes in sea surface temperatures and coral bleaching within a Caribbean coral reef

Elevated sea surface temperature (SST) caused by global warming is one of the major threats to coral reefs. While increased SST has been shown to negatively affect the health of coral reefs by increasing rates of coral bleaching, how changes to atmospheric heating impact SST distributions, modified by local flow environments, has been less understood. This study aimed to simulate future water flow patterns and water surface heating in response to increased air temperature within a coral reef system in Bocas del Toro, Panama, located within the Caribbean Sea. Water flow and SST were modeled using the Delft3D-FLOW© computer simulation package. Locally measured physical parameters, including bathymetry, astronomic tidal forcing, and coral habitat distribution were input into the model and water flow, and SST was simulated over a four-month period under present day, as well as projected warming scenarios in 2020s, 2050s, and 2080s. Changes in SST, and hence the thermal stress to corals, were quantified by degree heating weeks. Results showed that present-day reported bleaching sites were consistent with localized regions of continuous high SST. Regions with highest SST were located within shallow coastal sites adjacent to the mainland or within the interior of the bay, and characterized by low currents with high water retention times. Under projected increases in SSTs, shallow reef areas in low flow regions were found to be hot spots for future bleaching.

A continuous, real-time water quality monitoring system for the coral reef ecosystems of Nanwan Bay, Southern Taiwan

The coral reef ecosystems of Nanwan Bay, Southern Taiwan are undergoing degradation due to anthropogenic impacts, and as such have resulted in a decline in coral cover. As a first step in preventing the continual degradation of these coral reef environments, it is important to understand how changes in water quality affect these ecosystems on a fine-tuned timescale. To this end, a real-time water quality monitoring system was implemented in Nanwan Bay in 2010. We found that natural events, such as cold water intrusion due to upwelling, tended to elicit temporal shifts in coral spawning between 2010 and 2011. In addition, Degree Heating Weeks (DHWs), a commonly utilized predictor of coral bleaching, were 0.92 and 0.59 in summer 2010 and 2011, respectively. Though this quantity of DHW was below the presumed stress-inducing value for these reefs, a rise in DHWs in the future may stress the resident corals.

Opposite latitudinal gradients in projected ocean acidification and bleaching impacts on coral reefs

Coral reefs and the services they provide are seriously threatened by ocean acidification and climate change impacts like coral bleaching. Here, we present updated global projections for these key threats to coral reefs based on ensembles of IPCC AR5 climate models using the new Representative Concentration Pathway (RCP) experiments. For all tropical reef locations, we project absolute and percentage changes in aragonite saturation state (Ωarag) for the period between 2006 and the onset of annual severe bleaching (thermal stress >8 degree heating weeks); a point at which it is difficult to believe reefs can persist as we know them. Severe annual bleaching is projected to start 10-15years later at high-latitude reefs than for reefs in low latitudes under RCP8.5. In these 10-15years, Ωarag keeps declining and thus any benefits for high-latitude reefs of later onset of annual bleaching may be negated by the effects of acidification. There are no long-term refugia from the effects of both acidification and bleaching. Of all reef locations, 90% are projected to experience severe bleaching annually by 2055. Furthermore, 5% declines in calcification are projected for all reef locations by 2034 under RCP8.5, assuming a 15% decline in calcification per unit of Ωarag. Drastic emissions cuts, such as those represented by RCP6.0, result in an average year for the onset of annual severe bleaching that is ~20years later (2062 vs. 2044). However, global emissions are tracking above the current worst-case scenario devised by the scientific community, as has happened in previous generations of emission scenarios. The projections here for conditions on coral reefs are dire, but provide the most up-to-date assessment of what the changing climate and ocean acidification mean for the persistence of coral reefs.

Atmospheric forcing intensifies the effects of regional ocean warming on reef‐scale temperature anomalies during a coral bleaching event

We investigate how local atmospheric conditions and hydrodynamic forcing contributed to local variations in water temperature within a fringing coral reef‐lagoon system during the peak of a marine heat wave in 2010–2011 that caused mass coral bleaching across Western Australia. A three‐dimensional circulation model Regional Ocean Modeling System (ROMS) with a built‐in air‐sea heat flux exchange module Coupled Ocean Atmosphere Experiment (COARE) was coupled with a spectral wave model Simulating Waves Nearshore (SWAN) to resolve the surface heat exchange and wave‐driven reef circulation in Coral Bay, Ningaloo Reef. Using realistic oceanic and atmospheric forcing, the model predictions were in good agreement with measured time series of water temperature at various locations in the coral reef system during the bleaching event. Through a series of sensitivity analyses, we found that the difference in temperature between the reef and surrounding offshore waters (ΔT) was predominantly a function of both the daily mean net heat flux ( ) and residence time, whereas diurnal variations in reef water temperature were dependent on the diurnal fluctuation in the net heat flux. We found that reef temperatures were substantially higher than offshore in the inner lagoon under normal weather conditions and over the entire reef domain under more extreme weather conditions (0.7°C–1.5°C). Although these temperature elevations were still less than that caused by the regional ocean warming (2°C–3°C), the arrival of peak seasonal temperatures in the summer of 2010–2011 (when net atmospheric heat fluxes were positive and abnormally high) caused substantially higher thermal stresses than would have otherwise occurred if offshore temperatures had reached their normal seasonal maxima in autumn (when net atmospheric heat fluxes were negative or cooling). Therefore, the degree heating weeks calculated based on offshore temperature substantially underestimated the thermal stresses experienced by the reef in the period leading up to the observed bleaching event (3 versus 11°C‐weeks).

Increasing temperature anomalies reduce coral growth in the Weizhou Island, northern South China Sea

The ways in which high-latitude corals respond to ongoing climate warming and the increasing incidence of extreme warm- and cold-water events remains unclear, probably due to a lack of field studies, especially in the northern South China Sea (NSCS). In this study, temporal variation in the skeletal growth rate in massive Porites lutea corals collected from the Weizhou Island, NSCS, was examined over a 27-year period (from 1984 to 2010). The coral skeletal extension rates were determined by using X-ray photography, and compared to the Degree Heating Weeks (DHWs) index (0–16.7 °C-weeks) and the Sea Surface Temperature (SST) Anomalies (0–0.6 °C for + SST_anomaly, and −3.2–0 °C for -SST_anomaly). Historical extreme high and low temperature events were calculated to estimate warm- (DHW > 6 °C-weeks, +SST_anomaly > 0.2 °C) and cold- (-SST_anomaly < −1.6 °C) water stresses on reef-building corals. The average skeletal growth rate for all coral colonies was 6.3 mm year−1, ranging from 3.1 to 9.9 mm year−1. Coral skeletal growth consistently showed a downward trajectory, especially after the year of 1997. The mean value was 7.3 mm year−1 from 1984 to 1996 and then declined by approximately 26% to 5.4 mm year−1 from 1997 to 2010. We found that an increasing frequency and intensity in warm- and cold-stresses can explain the observed decline in growth rate of Porites colonies in the Weizhou Island.

Susceptibility of central Red Sea corals during a major bleaching event

A major coral bleaching event occurred in the central Red Sea near Thuwal, Saudi Arabia, in the summer of 2010, when the region experienced up to 10–11 degree heating weeks. We documented the susceptibility of various coral taxa to bleaching at eight reefs during the peak of this thermal stress. Oculinids and agaricids were most susceptible to bleaching, with up to 100 and 80 % of colonies of these families, respectively, bleaching at some reefs. In contrast, some families, such as mussids, pocilloporids, and pectinids showed low levels of bleaching (<20 % on average). We resurveyed the reefs 7 months later to estimate subsequent mortality. Mortality was highly variable among taxa, with some taxa showing evidence of full recovery and some (e.g., acroporids) apparently suffering nearly complete mortality. The unequal mortality among families resulted in significant change in community composition following the bleaching. Significant factors in the likelihood of coral bleaching during this event were depth of the reef and distance of the reef from shore. Shallow reefs and inshore reefs had a higher prevalence of bleaching. This bleaching event shows that Red Sea reefs are subject to the same increasing pressures that reefs face worldwide. This study provides a quantitative, genus-level assessment of the vulnerability of various coral groups from within the Red Sea to bleaching and estimates subsequent mortality. As such, it can provide valuable insights into the future for reef communities in the Red Sea.

Coral bleaching at Little Cayman, Cayman Islands 2009

The global rise in sea temperature through anthropogenic climate change is affecting coral reef ecosystems through a phenomenon known as coral bleaching; that is, the whitening of corals due to the loss of the symbiotic zooxanthellae which impart corals with their characteristic vivid coloration. We describe aspects of the most prevalent episode of coral bleaching ever recorded at Little Cayman, Cayman Islands, during the fall of 2009. The most susceptible corals were found to be, in order, Siderastrea siderea, Montastraea annularis, and Montastraea faveolata, while Diplora strigosa and Agaricia spp. were less so, yet still showed considerable bleaching prevalence and severity. Those found to be least susceptible were Porites porites, Porites astreoides, and Montastraea cavernosa. These observations and other reported observations of coral bleaching, together with 29 years (1982–2010) of satellite-derived sea surface temperatures, were used to optimize bleaching predictions at this location. To do this a Degree Heating Weeks (DHW) and Peirce Skill Score (PSS) analysis was employed to calculate a local bleaching threshold above which bleaching was expected to occur. A threshold of 4.2 DHW had the highest skill, with a PSS of 0.70. The method outlined here could be applied to other regions to find the optimal bleaching threshold and improve bleaching predictions.

Classification of remote Pacific coral reefs by physical oceanographic environment

[1] The oceanographic environment is a key element in structuring coral reef ecosystems by setting the range of physical and chemical conditions in which coral reef-builders live. A cluster analysis of physical and chemical oceanographic data is used to classify coral habitats in the remote tropical and subtropical Pacific Ocean based on average temperature, temperature seasonal cycle, nutrient levels, salinity, aragonite saturation state, storm frequency, intense hurricane hits, and dissolved oxygen as well as temperature anomalies in degree heating weeks. The resulting seven geographic habitats are stable to perturbations in types of data used in the cluster analysis. Based on recent coral reef survey data in the area, the coral cover was related to the identified geographic regions. The habitats tend to be geographically clustered, and each is characterized by a unique combination of oceanographic conditions. Previous studies suggest coral reef habitats are associated with a uniform array of oceanographic conditions, while our results demonstrate that finer-scale variations in physical variables may control coral reef environments. The results better define the physical environment of remote coral reefs, forming a foundation for future work addressing physical habitat perturbation and anthropogenic impacts on reefs.

Coral mortality associated with thermal fluctuations in the Phoenix Islands, 2002–2005

The Phoenix Islands (Republic of Kiribati, 172–170°W and 2.5–5°S) experience intra- and inter-annual sea surface temperature variability of ≈2°C and have few local anthropogenic impacts. From July 2002, a thermal stress event occurred, which peaked at 21 Degree Heating Weeks (DHW) in January 2003 and persisted for 4 years. Such thermal stress was greater than any thermal event reported in the coral reef literature. Reef surveys were conducted in July 2000, June 2002, and May 2005, for six of the eight islands. Sampling was stratified by exposure (windward, leeward, and lagoon) and depth (5, 10, 15, and 25 m). The thermal stress event caused mass coral mortality, and coral cover declined by approximately 60% between 2002 and 2005. However, mortality varied among sites (12–100%) and among islands (42–79%) and varied in accordance with the presence of a lagoon, island size, and windward vs. leeward exposure. Leeward reefs experienced the highest and most consistent decline in coral cover. Island size and the presence of a lagoon showed positive correlations with coral mortality, most likely because of the longer water residence time enhancing heating. Windward reefs showed cooler conditions than leeward reefs. Recently dead corals were observed at depths >35 m on windward and >45 m on leeward reefs. Between-island variation in temperature had no effect on between-island variation in coral mortality. Mortality levels reported here were comparable to those reported for the most extreme thermal stress events of 9–10 DHW in other regions. These results highlight the high degree of acclimation and/or adaptation of the corals in the Phoenix Islands to their local temperature regime, and their consequent vulnerability to anomalous events. Moreover, the results suggest the need to adjust thermal stress calculations to reflect local temperature variation.

Caribbean Corals in Crisis: Record Thermal Stress, Bleaching, and Mortality in 2005

BackgroundThe rising temperature of the world's oceans has become a major threat to coral reefs globally as the severity and frequency of mass coral bleaching and mortality events increase. In 2005, high ocean temperatures in the tropical Atlantic and Caribbean resulted in the most severe bleaching event ever recorded in the basin.Methodology/Principal FindingsSatellite-based tools provided warnings for coral reef managers and scientists, guiding both the timing and location of researchers' field observations as anomalously warm conditions developed and spread across the greater Caribbean region from June to October 2005. Field surveys of bleaching and mortality exceeded prior efforts in detail and extent, and provided a new standard for documenting the effects of bleaching and for testing nowcast and forecast products. Collaborators from 22 countries undertook the most comprehensive documentation of basin-scale bleaching to date and found that over 80% of corals bleached and over 40% died at many sites. The most severe bleaching coincided with waters nearest a western Atlantic warm pool that was centered off the northern end of the Lesser Antilles.Conclusions/SignificanceThermal stress during the 2005 event exceeded any observed from the Caribbean in the prior 20 years, and regionally-averaged temperatures were the warmest in over 150 years. Comparison of satellite data against field surveys demonstrated a significant predictive relationship between accumulated heat stress (measured using NOAA Coral Reef Watch's Degree Heating Weeks) and bleaching intensity. This severe, widespread bleaching and mortality will undoubtedly have long-term consequences for reef ecosystems and suggests a troubled future for tropical marine ecosystems under a warming climate.

Heating rate and symbiont productivity are key factors determining thermal stress in the reef-building coral Acropora formosa

The onset of large-scale coral bleaching events is routinely estimated on the basis of the duration and intensity of thermal anomalies determined as degree heating weeks. Degree heating weeks, however, do not account for differential rates of heating. This study aimed to explore the relationship between different rates of heating above the documented regional winter threshold, and resultant bleaching of the reef-building coral Acropora formosa. Under a relatively low light field, rapid heating of 1 degrees C day(-1) from 29 degrees C to 32 degrees C lead to a 17.6% decline in F(v)/F(m), concurrent with a rapid increase in xanthophyll de-epoxidation sustained into the dark, whereas slower heating rates of 0.5 degrees C day(-1) lead to no decline in F(v)/F(m) and no change in dark-adapted xanthophyll cycling. At the winter bleaching threshold of 30 degrees C, areal net O(2) evolution exceeded the control values for rapidly heated corals, but was lower than the controls for slowly heated corals. At the maximum temperature of 33 degrees C, however, both treatments had net O(2) fluxes that were 50% of control values. At 30 degrees C, only symbiont densities in the slowly heated controls were reduced relative to controls values. By 33 degrees C, however, symbiont densities were 55% less than the controls in both treatments. The rate of heat accumulation was found to be an important variable, with rapidly heated corals attaining the same bleaching status and loss of areal O(2) production for half the degree heating week exposure as slowly heated corals. The study revealed that it is incorrect to assume that significant dark acclimation disables non-photochemical quenching, because 75% of an increased xanthophyll pool was found to be in the de-epoxidated state following rapid heat accumulation. This has important ramifications for the interpretation of chlorophyll fluorescence data such as dark adapted F(v)/F(m).

Building an Automated Integrated Observing System to Detect Sea Surface Temperature Anomaly Events in the Florida Keys$^{\ast}$

<para xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> Satellite-derived sea surface temperature (SST) images have had limited applications in near-shore and coastal environments due to inadequate spatial resolution, incorrect geocorrection, or cloud contamination. We have developed a practical approach to remove these errors using Advanced Very High Resolution Radiometer (AVHRR) and MODerate-resolution Imaging Spectroradiometer (MODIS) 1-km resolution data. The objective was to improve the accuracy of SST anomaly estimates in the Florida Keys and to provide the best quality (in particular, high temporal and spatial resolutions) SST data products for this region. After manual navigation of over 47 000 AVHRR images (1993–2005), we implemented a cloud-filtering technique that differs from previously published image processing methods. The filter used a 12-year climatology and <formula formulatype="inline"><tex Notation="TeX">$\pm$</tex> </formula>3-day running SST statistics to flag cloud-contaminated pixels. Comparison with concurrent ( <formula formulatype="inline"><tex Notation="TeX">$\pm$</tex></formula>0.5 h) data from the SEAKEYS <emphasis emphasistype="italic"> in situ</emphasis> stations in the Florida Keys showed near-zero bias errors <formula formulatype="inline"><tex Notation="TeX"> $(≪ 0.05\ ^{\circ}\hbox{C})$</tex></formula> in the weekly anomaly for SST anomalies between <formula formulatype="inline"><tex Notation="TeX">$-$</tex></formula>3 <formula formulatype="inline"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex> </formula> and 3 <formula formulatype="inline"><tex Notation="TeX">$^{\circ}\hbox{C}$</tex></formula>, with standard deviations <formula formulatype="inline"><tex Notation="TeX">$≪ 0.5\ ^{\circ}\hbox{C}$</tex></formula>. The cloud filter was implemented using Interactive Data Language for near-real-time processing of AVHRR and MODIS data. The improved SST products were used to detect SST anomalies and to estimate degree-heating weeks (DHWs) to assess the potential</para>

Sea-surface temperature and thermal stress in the Coral Triangle over the past two decades

Increasing ocean temperature has become one of the major concerns in recent times with reports of various related ecological impacts becoming commonplace. One of the more notable is the increased frequency of mass coral bleaching worldwide. This study focuses on the Coral Triangle region and utilizes the National Oceanic and Atmospheric Administration-Coral Reef Watch (NOAA-CRW) satellite-derived sea surface temperature (SST) and Degree Heating Weeks (DHW) products to investigate changes in the thermal regime of the Coral Triangle waters between 1985 and 2006. Results show an upward trend in SST during this period with an average rate of 0.2°C/decade. However, warming within this region is not uniform, and the waters of the northern and eastern parts of the Coral Triangle are warming fastest. Areas in the eastern part have experienced more thermal stress events, and these stress events appear to be more likely during a La Nina.

Building an Automated Integrated Observing System to Detect Sea Surface Temperature Anomaly Events in the Florida Keys

Satellite-derived sea surface temperature (SST) images have had limited applications in near-shore and coastal environments due to inadequate spatial resolution, incorrect geocorrection, or cloud contamination. We have developed a practical approach to remove these errors using Advanced Very High Resolution Radiometer (AVHRR) and MODerate-resolution Imaging Spectroradiometer (MODIS) 1-km resolution data. The objective was to improve the accuracy of SST anomaly estimates in the Florida Keys and to provide the best quality (in particular, high temporal and spatial resolutions) SST data products for this region. After manual navigation of over 47 000 AVHRR images (1993-2005), we implemented a cloud-filtering technique that differs from previously published image processing methods. The filter used a 12-year climatology and plusmn3-day running SST statistics to flag cloud-contaminated pixels. Comparison with concurrent ( plusmn0.5 h) data from the SEAKEYS <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">in</i> <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">situ</i> stations in the Florida Keys showed near-zero bias errors (<0.05degC) in the weekly anomaly for SST anomalies between -3degC and 3degC, with standard deviations <0.5degC. The cloud filter was implemented using Interactive Data Language for near-real-time processing of AVHRR and MODIS data. The improved SST products were used to detect SST anomalies and to estimate degree-heating weeks (DHWs) to assess the potential for coral reef stress. The mean and anomaly products are updated weekly, with periodic updates of the DHW products, on a Web site. The SST data at specific geographical locations were also automatically ingested in near real time into National Oceanic and Atmospheric Administration's (NOAA) Integrated Coral Observing Network Web-based application to assist in management and decision making through a novel expert system tool (G2) implemented at NOAA.

Quantifying the quality of coral bleaching predictions

Techniques that utilize sea surface temperature (SST) observations to predict coral reef bleaching are in common use and form the foundation for predicted global coral reef ecosystem demise within this century. Yet, quality assessments of these methods are typically qualitative or anecdotal. Quality is the correspondence of forecasts with observations and has standard quantitative measures. Here a forecast verification method, commonly used in meteorology, is presented and used to measure the quality of the degree heating weeks (DHW) technique as an exploration of insights that can be gleaned from this methodology. DHW values were calculated from NOAA Optimum Interpolation SST version 2 data and compared to a database of bleaching observations from 1990–2007. Quality is expressed with an objective measure, the Peirce Skill Score (PSS). The quality at varying DHW thresholds above which bleaching was projected to occur is calculated. By selecting the thresholds that maximize quality, the predictive technique is objectively optimized. This results in optimal threshold maps, showing reefs more prone and more resistant to bleaching. Optimization increases the quality of DHW as a predictor of bleaching from PSS = 0.55 to PSS = 0.83, in global average, but the optimal PSS and corresponding DHW values vary significantly from location to location. The coral reef research and management community are urged to adopt the simple, but rigorous tools of forecast verification routinely used in other disciplines so that bleaching forecasts can be quantitatively compared and their quality improved.