Overview of NOAA coral reef watch program's near-real time satellite global coral bleaching monitoring activities

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Overview of NOAA Coral Reef Watch Program’s Near-Real-
Time Satellite Global Coral Bleaching Monitoring Activities
Gang LIU
1
, Alan E. STRONG
2
, William SKIRVING
3
, and L. Felipe ARZAYUS
4
1
STG, Inc., NOAA, E/RA31, SSMC1, Room 5310, 1335 East-West Highway, Silver Spring, MD 20910, USA;
Gang.Liu@noaa.gov
2
NOAA/NESDIS/ORA, E/RA3, WWB, Room 601, 5200 Auth Road, Camp Springs, MD 20746, USA;
Alan.E.Strong@noaa.gov
3
CIRA, Colorado State University, NOAA, E/RA31, SSMC1, Room 5306, 1335 East-West Highway, Silver Spring,
MD 20910, USA; William.Skirving@noaa.gov
4
I. M. Systems Group, Inc., NOAA, E/RA31, SSMC1, Room 5308, 1335 East-West Highway, Silver Spring, MD
20910, USA; Felipe.Arzayus@noaa.gov
Abstract Coral bleaching has been considered as one of
the major contributors to the increased worldwide
deterioration of coral reef ecosystems being reported
over the past few decades. Understandably the need for
improved understanding, monitoring, and prediction of
coral bleaching becomes imperative. Satellite remote
sensing has become a key tool for coral reef managers
and scientists, providing the capability of synoptic views
of the global oceans in near-real-time and the ability to
monitor remote reef areas. As early as 1997, NOAA’s
National Environmental Satellite, Data, and Information
Service (NESDIS) began producing near-real-time, web-
accessible, satellite-derived sea surface temperature
(SST) products to monitor conditions conducive to coral
bleaching from thermal stress around the globe. In 2000,
this activity enabled the genesis of NOAA’s Coral Reef
Watch (CRW) Program. Over the past couple of years,
most of its key products, including SST anomalies,
bleaching HotSpots, Degree Heating Weeks (DHW), and
Tropical Ocean Coral Bleaching Indices webpage
became “operational” products after successfully
providing early warnings of coral bleaching to the U.S.
and global coral reef communities as “experimental”
products for several years. Currently, several new near-
real-time products, including Short-Term Trends of
Thermal Stress, Duration of Thermal Stress, Number of
Stress Days, and an automated e-mail alerting system,
are in the final stages of development and should become
available soon. As we attempt to improve the accuracy of
the monitoring products and develop prediction
capabilities, CRW is seeking to develop these products at
higher spatial resolutions, monitor other related
environmental parameters (such as surface wind, solar
radiation, and wave field), incorporate numerical model
simulations, and develop new and more accurate
algorithms. CRW’s mission is to provide the domestic
and international coral reef communities with timely and
accurate information for understanding, monitoring, and
preserving these “rainforests of the sea.”
Keywords coral, bleaching, satellite remote sensing, sea
surface temperature, HotSpot, Degree Heating Week,
monitoring
Introduction
Coral reefs are the most diverse and complex marine
ecosystem and comprise the largest biological structure
on the earth. Well-developed coral reefs reflect
thousands of years of history. Recently, however, coral
reefs have been facing increasing hazards and threats and
many coral habitats worldwide have been declining
rapidly (e.g., Glynn, 1996).
Most reef-forming corals contain symbiotic
microscopic algae within their gastrodermal cells (Yonge
and Nicholls, 1931). Healthy corals come in a variety of
colors, depending on the photosynthetic pigments of their
symbiotic algae. However, under certain environmental
stresses, the algae can be expelled by the host corals.
Lacking their symbiotic algae, the corals reveal their
white underlying calcium carbonate skeleton through the
translucent coral tissue and the affected coral colony
becomes stark white or pale in color. This phenomenon
is commonly known as “coral bleaching” (Berkelmans
and Willis, 1999; Reaser et al., 2000).
Coral bleaching is often caused by ambient water
temperatures that exceed the coral’s tolerance level (e.g.,
Glynn and D’Croz, 1990; Lesser et al., 1990). This may
be as little as 1 to 2
o
C above the mean monthly summer
values (Coles and Jokiel, 1977; Jokiel and Coles, 1990).
High temperature not only contributes to bleaching but
also reduces coral’s normal growth and reproductive
capacity (Szmant and Gassman, 1990; Ward et al., 1998;
Hoegh-Guldberg, 1999). Bleaching may also weaken
coral’s ability to fight disease (Cervino et al., 1998;
Richardson et al., 1998). Prolonged thermal stress over
bleached corals often leads to the death of the corals
(e.g., Hoegh-Guldberg, 1999; Wilkinson et al., 1999).
Severe bleaching events have dramatic long-term
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Proceedings of 10th International Coral Reef Symposium, 1783-1793 (2006)

ecological impacts, including loss of reef-building corals,
changes in benthic habitat, and, in some cases, changes
in fish population (Munro, 1996; Berkelmans and Oliver,
1999; Done, 1999). Even under favorable conditions, it
can take many years for severely bleached reefs to
recover (Hughes, 1994; Connell et al., 1997; Done,
1999).
Bleaching may occur at local scales or at geographic
scales. A mass bleaching event is a bleaching event
occurring at geographic scales that may involve entire
reef systems and geographic realms (Hoegh-Guldberg,
1999). Mass bleaching events occur much less frequently
than local scale bleaching events which are often caused
by local environmental factors.
Climate change is considered to be one of the
greatest threats to the world’s coral reefs over the next
few decades and may be somewhat responsible for large-
scale deterioration over the past few decades (Hughes et
al., 2003). Anomalously high sea surface temperatures
(SSTs) driven by natural climate events (e.g., 1997-1998
El Niño) occurring in association with rising sea
temperatures have caused large-scale mass coral
bleaching over the past few decades (i.e., Montgomery
and Strong, 1994; Hoegh-Guldberg, 1999; Goreau et al.,
2000; Wellington et al., 2001; Strong et al., 2002; Liu et
al., 2003). These changes have resulted in the loss of
reef-building corals on an unprecedented scale across
large areas of the world’s tropical oceans (Glynn, 1996;
Hoegh-Guldberg, 1999; Wilkinson, 1999).
Coral reef areas are being monitored more
extensively now than ever for environmental conditions
associated with bleaching. As early as 1997, the U.S.
National Oceanic and Atmospheric Administration
(NOAA)’s National Environmental Satellite, Data, and
Information Service (NESDIS) began to provide near-
real-time satellite remotely-sensed SSTs and extended
information, derived from SSTs, to the U.S. and global
coral reef communities as a means of detecting and
monitoring thermal stress conducive to bleaching. The
NESDIS satellite monitoring activity is now a core
component of NOAA’s Coral Reef Watch (CRW)
Program. An overview of the current near-real-time
global satellite coral bleaching monitoring activities at
NOAA’s CRW is given in this paper.
Development of the CRW near-real-time satellite
coral bleaching monitoring activities
Following several years of research projects in
collaboration with midshipmen from the U.S. Naval
Academy (e.g., Montgomery and Strong, 1994; Gleeson
and Strong, 1995), the world’s first near-real-time
satellite global bleaching monitoring system was
developed in 1996 at NOAA/NESDIS (Strong et al.,
1997). The near-real-time monitoring system was
inaugurated in 1997, providing web-accessible products
to both the U.S. and global coral reef communities. In
1997, the system included only one monitoring tool,
bleaching HotSpots (see the next section for the
description). By 2000, a suite of satellite global coral
bleaching monitoring tools had been developed at
NESDIS, including bleaching Degree Heating Weeks
(DHW, see the next section for the description). This
satellite bleaching monitoring system has been and still is
the only system of its kind available in the world and
possibly represents the only global suite of operational
satellite products currently being used for the
management of any marine ecosystem (Skirving et al.,
2005).
NOAA’s CRW (http://coralreefwatch.noaa.gov/)
was established in 2000 with NESDIS’ satellite
bleaching monitoring system serving as a core
component. NOAA’s CRW, established to provide early
warnings and long-term monitoring for both U.S. and
global coral reef ecosystems, is mainly a monitoring
program that includes both satellite and in-situ
monitoring components. Most of the in-situ monitoring
in CRW is conducted by NOAA's Office of Oceanic and
Atmospheric Research (OAR), National Marine Fisheries
Service (NMFS), and National Ocean Service (NOS). In
early 2004, the NOAA Coral Reef Ecosystem Integrated
Observing System (CREIOS) was established to
integrate NOAA's monitoring, mapping, and observing
of coral reef ecosystems by NESDIS, NMFS, OAR, and
NOS.
Suite of CRW near-real-time satellite global coral
bleaching monitoring tools
Currently, the primary CRW near-real-time satellite
global coral bleaching monitoring tools include the
operational near-real-time satellite global 50-km
nighttime SSTs, coral bleaching HotSpots, coral
bleaching DHWs, Tropical Ocean Coral Bleaching
Indices webpage, and SST time series for selected reef
sites (Fig. 1). Most of these primary products are
presented in graphic format and posted online for easy
global access. Animations of SST, HotSpot, and DHW
charts over the most recent 2, 4, and 6 months are also
produced and posted on the web. These products were
developed based on earlier work by Montgomery and
Strong (1994), Gleeson and Strong (1995), Strong et al.
(1997), and Goreau et al. (2000).
The coral bleaching HotSpot (Fig. 1a) is a type of
SST anomaly giving the difference between a nighttime
SST value (Fig. 1b) at a given time at a given location
and the corresponding climatology value for the same
location (Strong et al., 1997; Liu et al., 2003; Skirving et
al., 2005). The climatology currently used for deriving
the bleaching HotSpot is the climatological mean
temperature of the climatologically warmest month at the
location. It is often referred to as the maximum of the
monthly mean SST climatology, otherwise known as
MMM climatology. This climatology, derived from the
Polar-orbiting Operational Environmental Satellite
(POES) Advanced Very High Resolution Radiometer
(AVHRR) nighttime SSTs for the period 1985-1993, is
static in time for any given location, but varies
geographically. This satellite coral bleaching HotSpot
product was developed at NOAA/NESDIS in 1996 based
on the “ocean hot spots” concept introduced by Goreau
and Hayes (1994). From 1997, HotSpot was produced
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routinely as an experimental product to measure the
occurrence and intensity of anomalously high SSTs
(Strong et al., 1997) and became the first operational
product in September 2002. Pinpointing the location of
thermal stress conducive to coral bleaching in the global
tropical oceans, HotSpot charts display only positive
values of this specialized anomaly.
Fig. 1a. CRW’s operational twice-weekly near-real-time
satellite 50-km coral bleaching HotSpot charts of January
31, 2004 for the Eastern Hemisphere (upper chart) and
Western Hemisphere (lower chart).
Fig. 1b. CRW’s operational twice-weekly near-real-time
satellite global 50-km nighttime SST chart of January 31,
2004.
To measure the cumulative extent of thermal stress
experienced by coral reefs, a thermal stress index, called
a DHW (Fig. 1c), was also developed at NOAA/NESDIS
(Strong et al., 1997). It became available experimentally
for near-real-time monitoring at the beginning of 2000
and became an operational product in September 2003.
DHW for a given location represents the accumulation of
HotSpots at that location over a rolling 12-week time
period (Liu et al., 2003; Skirving et al., 2005).
Preliminary indications show that typically a HotSpot
value of less than one degree Celsius is insufficient to
cause visible stress on corals. Consequently, only
HotSpot values ≥1°C are accumulated (i.e., if there are
consecutive weekly HotSpot values of 1.0, 2.0, 0.8, and
1.2°C, the DHW value will be 4.2 because 0.8 is less
than one and, therefore, does not get accumulated). One
DHW is equivalent to one week of HotSpot levels
staying at 1°C or half a week of HotSpot levels at 2°C,
and so forth.
Fig. 1c. CRW’s operational twice-weekly near-real-time
satellite 50-km coral bleaching DHW charts of January
31, 2004 for the Eastern Hemisphere (upper chart) and
Western Hemisphere (lower chart).
Field observations (most of which are subjective
measurements presented as informal reports) with
coincident satellite data are only available for a limited
number of years, but do include the 1998 worldwide
mass bleaching events. Collectively, these observations
indicate that there is a correlation between bleached
corals and DHW values of four or greater (Liu et al.,
2003; Skirving et al., 2005). When DHW values reach
eight, widespread bleaching is likely and some mortality
can be expected. CRW has applied these DHW levels
when generating satellite bleaching warnings and alerts
(Wellington et al., 2001; Liu et al., 2003). These products
have been successful in monitoring major coral
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bleaching episodes around the globe since 1997 (e.g.,
Wilkinson et al., 1999; Goreau et al., 2000; Wellington et
al., 2001).
Fig. 1d. CRW’s operational twice-weekly near-real-time
satellite Tropical Ocean Coral Bleaching Indices
webpage of January 31, 2004, for 24 selected reef sites
around the globe.
CRW’s satellite Tropical Ocean Bleaching Indices
webpage (Fig. 1d) provides actual numerical values of
near-real-time SST and DHW, along with the MMM
climatology values, currently for 24 selected reef sites
around the globe. Numerical values typically offer more
accurate information than the information extracted from
graphic displays using color scales; whereas, the chart
overview provides extent and often shows connectivity
with adjacent reef systems. A small red triangular
warning sign (Fig. 1d) appears next to a reef name when
the SST at a representative satellite pixel closest to the
reef exceeds the MMM climatology value at the pixel;
whereas, a large red triangular warning sign appears next
to the reef name and the name is colored red when a
DHW value has accumulated during the past twice-
weekly time period. Among the 24 sites, six are in the
Atlantic Ocean (Bermuda, Sombrero Reef, Lee Stocking
Island, Puerto Rico, US Virgin Islands, and Glover’s
Reef Atoll); twelve in the Pacific Ocean (Midway Atoll,
Oahu-Maui, Palmyra Island, Galapagos, American
Samoa, Tahiti-Moorea, Guam, Enewetok, Palau, Davies
Reef, Heron Island, and Fiji-Beqa); and six in the Indian
Ocean (Oman-Muscat, Maldives-Male, Seychelles-
Mahe, Cobourg Park, Scott Reef, and Ningaloo Reef).
The page also provides numerous links to the
corresponding regional reef maps and satellite near-real-
time wind fields.
CRW’s satellite temperature time series webpage is
the entry point to the time series charts (Fig. 1e) of these
24 selected reef sites. These time series go back to 1985.
Animations of SST, HotSpot, and DHW charts over the
most recent 2-, 4-, and 6-month time periods (not shown)
are produced and posted online for easy monitoring of
the temporal development and spatial evolution of
thermal stress.
All of these near-real-time CRW products are
presently being updated twice-a-week in near-real-time
using the updated NOAA/NESDIS operational twice-
weekly composite satellite nighttime AVHRR SST field.
On Tuesdays, the twice-weekly satellite composite SST
data, derived from daily SST retrievals obtained from the
previous Saturday through Monday, are used for
updating bleaching products and, similarly, on Saturdays,
data from the previous Tuesday through Friday are used.
These near-real-time products, along with the
descriptions of methodologies, are web-accessible at
http://coralreefwatch.noaa.gov/satellite. All the static
twice-weekly data and charts are archived and also web-
accessible at the above website. The animations are not
archived.
Fig. 1e. CRW’s operational twice-weekly near-real-time
satellite SST time series chart as of July 27, 2004, for a
representative pixel closest to Sombrero Reef, Florida.
The static MMM climatology value (black dashed line)
and MMM+1ºC (red line) at the pixel are also plotted.
Application of the CRW satellite coral bleaching
monitoring tools: a demonstration
In this section, a mass coral bleaching event is used
as a sample to demonstrate how the CRW near-real-time
monitoring tools are applied for detecting the occurrence
and monitoring the development of thermal stress
responsible for a bleaching event.
During the summer of 2002, a mass coral bleaching
was observed in the Northwestern Hawaiian Islands
(NWHI). This bleaching event was reported as the first
mass bleaching event ever observed in this remote and
relatively pristine large-scale coral reef ecosystem (Aeby
et al., 2003). A series of CRW near-real-time, twice-
weekly, HotSpot charts (Fig. 2) shows the development
of the thermal stress in the North Pacific Ocean at several
stages during the summer of 2002. These HotSpot charts
were modified from the original near-real-time global
HotSpot charts to show only the North Pacific Ocean.
The original near-real-time, twice-weekly, HotSpot
charts are archived and web-accessible at
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http://www.osdpd.noaa.gov/PSB/EPS/SST/climohot_200
2.html. Near-real-time animations of HotSpots charts
were also used at the time for monitoring the evolving
development of the thermal stress across the region. The
little cross on the charts in Fig. 2 marks the location of
Midway Atoll of the NWHI, which is near the northwest
end of the NWHI. In the NWHI region, the thermal
stress, shown by positive HotSpots, first appeared in late
July, reached its maximum strength in early August,
achieved its maximum spatial coverage in the NWHI in
late August, and disappeared from the region by late
September. The accumulation of DHW in the NWHI
lasted over 10 weeks. The thermal stress first developed
in the region west-northwest of the NWHI and then
expanded east-southeastward into the NWHI. The
intensity of the HotSpot decreased as the thermal stress
evolved towards the southeast.
Fig. 2. CRW’s near-real-time HotSpot charts of July
23, August 12, 30, and September 24, 2002, showing the
development of thermal stress in the North Pacific
Ocean. The little cross on the charts marks the location
of Midway Atoll of the NWHI, which is near the
northwest end of the NWHI. The islands shown to the far
southeast of the Midway Atoll are the Main Hawaiian
Islands, which are off the southeast end of the NWHI.
A series of CRW near-real-time, twice-weekly,
DHW charts (Fig. 3) shows the development of the
extent of thermal stress accumulation in the North Pacific
Ocean during the same time period. The original near-
real-time charts are archived and web-accessible at
http://www.osdpd.noaa.gov/PSB/EPS/SST/dhw_retro_20
02.html. The accumulation of DHW in the NWHI region
started in late July and continued into early September.
Maximum DHW accumulations decreased towards the
southeast in the NWHI.
Fig. 3. CRW’s near-real-time DHW charts of July 26
and September 9, 2002, showing the accumulation of
thermal stress in the North Pacific Ocean during the 2002
mass coral bleaching event in the NWHI. See Fig. 2 for
the location of the NWHI.
Satellite SST time series (Fig. 4) show that, among
the reef areas in the NWHI region, the three
northwestern-most atolls, Kure, Midway, and Pearl and
Hermes, bore the worst of the thermal stress. The 50-km
satellite pixels closest to these three atolls are centered at
(28.5N, 178.0W), (28.5N, 177.5W), and (28.0N,
176.0W), respectively. At these three satellite pixels, the
maximum DHW values during the summer of 2002 were
6.0, 7.6, and 6.4 DHWs, respectively, with the maximum
HotSpot values of 1.9, 1.9, and 1.6°C.
Midway Atoll is one of the 24 selected reef sites on
our Tropical Ocean Coral Bleaching Indices webpage
(Fig. 1d). In early August of 2002, when the satellite SST
quickly exceeded the MMM climatology value and
DHW started to accumulate in a large area that included
Midway Atoll (Fig. 5), an early warning for potential
bleaching was issued by CRW via emails (NOAA’s
“coral-list”) to coral reef scientists and managers in the
region. Several follow-up bleaching warnings were
issued when a large area in the NWHI experienced more
than 4 DHWs. The elevated water temperatures were also
detected by the automated in-situ Coral Reef Early
Warning System (CREWS) buoys, operated in the area
by NOAA’s National Marine Fisheries Service (NMFS)
Coral Reef Ecosystem Division (CRED) (Hoeke et al.,
2004).
In September 2002, a field survey by CRED along
135 kilometers of prime reef habitat in the NWHI
verified this mass bleaching event (Aeby et al., 2003;
Hoeke et al., 2004; Kenyon et al., 2004). The cruise was
scheduled before the occurrence of the bleaching event,
but updated information from CRW helped CRED alter
their original cruise plan to focus more attention on
conducting surveys on mass coral bleaching that
previously was not considered a significant threat in this
region.
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Fig. 4. CRW’s near-real-time satellite SST time series
charts of 2002 showing the temperature evolution at the
three northwestern-most atolls of the NWHI: Kure,
Midway, and Pearl and Hermes. The static MMM
climatology value (black dashed lines) and MMM+1ºC
(red lines) at these pixels are also plotted.
Substantial and unprecedented bleaching (greater
than 20% and up to 100% of the corals) was observed on
reefs at the three northwestern-most atolls, Kure,
Midway, and Pearl and Hermes, with diminished
bleaching in other NWHI reefs towards the southeast
(Aeby et al., 2003; Kenyon et al., 2004). Bleaching was
initially reported in August 2002 by the CRED-led
NWHI marine debris removal team and mass bleaching
was first reported in September 2002 (Aeby et al., 2003).
CRW’s satellite monitoring of this mass bleaching event
matched very well with the in-situ observations in both
pattern and timing of the bleaching.
Some recent noteworthy mass bleaching events
detected by CRW
Since the inauguration of the CRW satellite
monitoring in 1997, many mass coral bleaching events
have taken place around the globe. In this section, as
noteworthy events, some of these bleaching events are
mentioned together with their CRW near-real-time
HotSpots and DHW charts, which identified the location,
spatial coverage, and intensity of the thermal stresses
responsible. The 2002 mass bleaching event in the
NWHI has already been discussed in the previous section
and is not described in this section.
2003: A mass coral bleaching event was observed in
Bermuda during the summer of 2003 (Cook CB, Smith
SR, Brylewska H, de Putron S, Webster G, Strong M,
pers. comm.). Of all the coral colonies recorded during a
survey at the end of August and beginning of September,
21% were bleached at the rim reef sites and 19% were
bleached at the lagoonal sites. Of the most affected coral
species, 94% of the colonies were bleached on the rim
reefs and 77% on the lagoonal reefs. Fig. 6 shows the
HotSpot at its peak intensity in mid-August in the
northwest Atlantic Ocean and the maximum
accumulation of DHW in late-August. The maximum
HotSpot and DHW values at Bermuda were 1.8°C and
9.8 DHWs, respectively.
Fig. 5. CRW’s Tropical Ocean Bleaching Indices
webpages showing thermal stress information and related
bleaching warning levels for Midway Atoll on July 22
(upper panel), August 2 (middle panel), and September
6, 2002 (lower panel).
2002: In early 2002, during the austral summer, an
unprecedented mass coral bleaching event was recorded
in the Great Barrier Reef (GBR), Australia (Wilkinson,
2002b; Liu et al., 2003). This bleaching event was much
worse than the 1998 mass bleaching event in the GBR in
terms of both intensity and spatial coverage. Almost 60%
of the total GBR reef area was affected with few reefs
escaping the bleaching. Up to 90% of corals were dead at
the worst affected sites (Wilkinson, 2002b). Fig. 7 shows
the distribution of HotSpot at its peak intensity and the
maximum DHW in the GBR during early 2002. The
thermal stress peaked around February 11, 2002 when
widespread HotSpots over the GBR reached maximum
levels between 2°C and 3°C. The maximum DHW
accumulation for the region occurred just east of the
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GBR (up to 16 DHWs); while throughout the region, the
maximum accumulations exceeded 10 DHWs (Liu et al.,
2003).
Fig. 6. CRW’s HotSpot chart (upper chart) showing the
thermal stress during its peak stage in mid-August 2003
in the Northwest Atlantic Ocean and DHW chart (lower
chart) showing the maximum accumulation of DHW in
late-August 2003.
2001: Fig. 8 shows the peak HotSpots and the
maximum DHW accumulation in the Northwest Pacific
Ocean during the 2001 summer, when a mass coral
bleaching event occurred in the Ryukyu Islands, Japan
(Strong et al., 2002). In the Ryukyu Islands, the
persistent HotSpot reached its maximum intensity
(around 3°C, immediately east of Okinawa) in mid-
August; the accumulation of DHW started in late June
and reached its maximum (more than 10 DHWs
immediately east of Okinawa) in mid-September. Field
observation showed that the most severe coral mortality
reached 46-69% in the southern islands of Ryukyus (Dai
et al., 2002).
2000: Fig. 9 shows the HotSpots at its peak
intensity and the maximum DHW accumulation in early
2000 around and near Easter Island in the South Pacific
Ocean. A mass coral bleaching event was observed at
Easter Island during the same time period (Wellington et
al., 2001). In this region, a HotSpot first appeared in
early February and by March 21, a DHW value of 9 had
accumulated at Easter Island. Survey at five widely
distributed sites around the island revealed that an
average of 85-90% of the coral colonies was affected
down to a depth of 10 m (Wellington et al., 2001).
1998: A strong ENSO event occurred during 1998,
coinciding with the observation of mass coral bleaching
events around the globe (e.g., Wilkinson et al., 1999;
Goreau et al., 2000; Wilkinson, 2002a). This world's
largest coral bleaching and mortality event temporarily
destroyed about 16% of the world's reefs. Large parts of
the Indian Ocean, Southeast Asia and the far western
Pacific were most dramatically affected, with mortality
levels greater than 90% on some reefs (Wilkinson,
2002a). Fig. 10 presents a composite maximum DHW
chart for 1998, showing the maximum accumulation of
DHW in the global oceans during the year. The
accumulation of thermal stress in the Eastern Equatorial
Pacific Ocean is obviously due to the 1997-1998 El Niño
event. Although the Eastern Equatorial Pacific Ocean is
not a coral rich region, unprecedented global distribution
of intensive thermal stress conducive to bleaching is
considered to be associated with the 1997-1998 El Niño
event.
Fig. 7. CRW’s HotSpot chart (upper chart) showing the
thermal stress during its peak stage and DHW chart
(lower chart) showing the maximum accumulation of
DHW in the Great Barrier Reef, Australia and adjacent
waters in early 2002.
Since 1997, CRW has issued many bleaching
warnings via the internet (“e-warnings”). Verification,
using the bleaching status reports sent directly to us from
users in the field and obtained from the ReefBase Project
of the World Fish Center, has proven most of our
warnings informing users that bleaching was occurring to
be correct. These warnings were issued when the values
of DHW, i.e., the accumulation of thermal stress,
exceeded a level of four with significant spatial coverage
at the locations of interest. Detailed statistical analyses of
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the accuracy of our satellite HotSpot/DHW monitoring
products are in progress, with results in a future
publication.
Fig. 8. CRW’s HotSpot chart (left chart) showing the
thermal stress during its peak stage and DHW chart
(right chart) showing the maximum accumulation of
DHW in the Northwest Pacific Ocean during the summer
of 2001.
Fig. 9. CRW’s HotSpot chart (upper chart) showing the
thermal stress during its peak stage and DHW chart
(lower chart) showing the maximum accumulation of
DHW in the South Pacific Ocean in early 2000.
Growing user group of CRW satellite near-real-time
coral bleaching monitoring tools
Over these past 8 years, CRW near-real-time
satellite global bleaching monitoring has gained
international recognition, credibility, and visibility. An
early pay-off was derived from successful CRW satellite
monitoring of mass coral bleaching events in the Great
Barrier Reef, Australia, and accompanying in-situ
monitoring conducted within the Great Barrier Reef in
2001. A notable science and technology arrangement was
established in June 2001 between the Australian Institute
of Marine Science and the Great Barrier Reef Marine
Park Authority, both of The Commonwealth of Australia,
and the National Oceanic and Atmospheric
Administration of the United States of America
regarding scientific and technical cooperation in the area
of coral reefs. This achievement represents the first
science and technology arrangement between the two
governments. The purpose of this arrangement is to
jointly pursue scientific and technical cooperation in the
area of coral reef research, monitoring, and protection
that further the mutual interests of the parties involved.
Australia’s rich experience and knowledge on the Great
Barrier Reef has already played a major role in the
development and improvement of both CRW satellite
and in-situ coral bleaching monitoring.
Since 2003, CRW’s near-real-time DHW data have
been provided on a monthly basis to the ReefBase
Project of the WorldFish Center. These DHW data are
loaded into ReefBase’s online GIS system as an
important GIS map layer (http://www.reefbase.org). In
this online GIS system, locations of reported bleaching
events collected by ReefBase can be superimposed on
CRW’s DHW maps to correlate the locations of observed
bleaching events and the values of DHW.
CRW’s HotSpot and DHW charts have been used by
various users in various bleaching related publications
(e.g., Ministry of the Environment and Japanese Coral
Reef Society, 2004; Richmond, 2002). They have also
appeared in various bleaching status reports and various
management, research, and educational newsletters and
websites (e.g.,
http://www.gbrmpa.gov.au/corp_site/info_services/science/blea
ching/conditions_report.html;
http://www.reeffutures.org/topics/bleach/present.cfm;
http://globalcoral.org/Grief%20on%20the%20Reef.htm;
http://www.pbs.org/wgbh/nova/elnino/reach/coral1.html;
http://globalcoral.org/Grief%20on%20the%20Reef.htm;
http://www.pgd.hawaii.edu/kaams/lpreef/crdanger/over.html;
http://www.eumetsat.de/en/area2/cgms/ap7-03.htm;
http://www.climatescience.gov/Library/stratplan2003/final/ccsp
stratplan2003-chap8.htm;
http://www.deh.gov.au/coasts/mpa/ashmore/volume-
2/chapter4.html
).
Fig. 10. CRW’s composite maximum DHW chart for
1998.
Ongoing developments and future plans
CRW has been working on developing new
algorithms and products to provide more accurate
monitoring tools for detecting and assessing thermal
stress conducive to coral bleaching and to provide more
timely information to the U.S. and global coral reef
communities.
At the time of writing this paper, CRW’s automated
Satellite Bleaching Alert (SBA) system has been
developed by CRW’s satellite monitoring efforts and is
in the final stage of operational implementation. The
SBA system is an automated coral bleaching e-mail alert
system to inform users, as soon as new satellite SST data
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are collected and processed, of the most up-to-date status
of thermal stress at the reefs of their interests. It will
become the second near-real-time alert system reported
in CRW’s near-real-time monitoring effort, after OAR’s
automated Near-Real-Time Data and Expert System of
CRW’s in-situ Coral Reef Early Warning System
(CREWS) Network. Once implemented, the e-mail alerts
will first be available for a number of selected reef sites
around the world. The system will automatically examine
the updated values of near-real-time satellite SST,
bleaching HotSpot, and DHW at the selected reef sites.
An automated e-mail will be sent to a subscriber for a
reef site only when the status level of thermal stress
changes at the site. No automated e-mail will be
generated if the status level remains the same, regardless
of the current status level. The status level of thermal
stress at selected reef sites will be updated twice per
week. For each reef location, five status levels have been
defined as follows: No Stress (HotSpot ≤ 0ºC), Bleaching
Watch (0ºC < HotSpot < 1ºC), Bleaching Warning
(HotSpot ≥ 1ºC and 0 < DHW < 4), Bleaching Alert
Level 1 (HotSpot ≥ 1ºC and 4 ≤ DHW < 8), and
Bleaching Alert Level 2 (HotSpot ≥ 1ºC and DHW ≥ 8).
Updated stress level, SST value, HotSpot value, DHW
value, and previous changes in stress level will be
included in each e-mail message, along with the web
addresses (URLs) leading subscribers to additional near-
real-time satellite monitoring data and charts. The details
of how to use the SBA e-mail alerts will be published by
CRW upon system implementation. Although a free
service, users will be requested to subscribe in order to
receive the automated e-mail alerts. Recipients will be
encouraged to provide reports on bleaching status and
feedback to the SBA system. It is anticipated that
additional reef sites will be added based on requests from
users.
Chart-based near-real-time short-term satellite SST
trends are also under development along with some other
new products. These trend products give the direction
and magnitude of the most recent SST changes during
the past one and two weeks ending at the most recent
update. Currently at 50-km resolution, CRW’s satellite
bleaching monitoring is capable of monitoring coral
bleaching only in association with large-scale thermal
stress having spatial coverage over both inshore and
offshore waters. Over the next few years, higher-
resolution products are planned to incorporate higher-
resolution SSTs to extend the monitoring capability from
basin- and regional-scale bleaching events to local- and
reef-scale bleaching events. Finally, building forecasting
capabilities is in CRW’s future plans. Plans for this goal
include incorporating numerical model simulations and
monitoring other environmental parameters together with
SST.
Summary
Since 1997, NOAA CRW’s near-real-time satellite
global coral bleaching monitoring system has become a
nationally and internationally respected tool for
monitoring coral bleaching. Satellite remote sensing
provides global coverage, reaching remote coral reef
ecosystems and providing synoptic views of the global
oceans. CRW operates the only satellite global bleaching
monitoring system in the world designed specifically to
help coral reef managers and scientists both map and
monitor anomalous SSTs and, hence, better understand
and predict mass coral bleaching. New and improved
products are anticipated by CRW for providing better
service to both the U.S. and global coral reef
communities.
The CREIOS’s goal is to provide both near-real-time
and long-term ecological and environmental observations
and information products over a broad range of spatial
and temporal scales, to understand the condition and
health of, and processes influencing, coral reef
ecosystems, and to assist stakeholders in making
improved and timely ecosystem-based management
decisions to conserve coral reefs.
Acknowledgements
Authors would like to take this chance to thank all the
other members who are presently involved in developing
and maintaining Coral Reef Watch’s near-real-time
satellite coral bleaching monitoring system: E. Bayler, J.
Sapper, L. Zhao, J. Wemmer, L. Evan, and S. Heron. The
views, opinions, and findings contained in this paper are
those of the author(s) and should not be construed as an
official National Oceanic and Atmospheric
Administration or U.S. Government position, policy, or
decision.
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