Usefulness
A reef assessment in the summer of 1999 found coral
mortality following this same latitudinal gradient. This
The use of SSTs, HotSpots and DHW has proven to
1998 bleaching event was the most severe event
be effective in describing conditions under which
recorded in the MAR. The 1995 and 2005 events did
bleaching is likely to occur. This indicator provides a
not have as high mortality of corals.
useful tool for monitoring efforts and management
Data
Data Needs
strategies that attempt to mitigate climate change
impacts.
Additional information is needed regarding the
following:
This indicator is particularly useful when combined
with other related indicators like F7 Coral Bleaching
· Inclusion of more areas in the MAR for automated
(to measure the extent of actual bleaching as predicted
bleaching alerts,
by this Index), along with subsequent monitoring of F5
Coral Mortality, F6 Coral Disease and S4 Coral
· Incorporation of other environmental data into the
Cover (to measure the actual impacts of the bleaching).
model (e.g., UV radiation levels, wind speeds),
Comparison with D13 Photic (Amphi) Index allows the
potential discrimination between temperature and UV
· Compiled data on historical bleaching events (extent
light (both widespread stressors capable of causing
and environmental conditions during the event),
bleaching events). The synthesis of this information
· Extent and severity of subsequent mortality
allows the ranking of reef resiliency to bleaching
(including coral disease outbreaks), and
presented in D15. Calibration of the satellite-derived
temperatures with in situ temperature measurements
· Identification of reef areas that are particularly
(within S8 Water Quality) is also important to
susceptible or particularly resistant or resilient to
understand local-scale bleaching patterns.
bleaching.
A limitation of the tool is that the one
MAR monitoring site, Glover's Reef,
is not necessarily representative
of the entire MAR region. However,
once an alert for Glover's Reef (or
anywhere in the Caribbean) is sent
out, reef managers throughout the
MAR can visit the website to look at
sea surface temperature anomalies
and DHW for their particular reef
area.
Status
Due to the coarse scale of the
available data, the information from
Belize can act as a surrogate for the
MAR region.
Looking back to the major bleaching
event of 1998, the latitudinal
variation in DHW can clearly be
seen in the following image taken
from the NOAA website.
Degree Heating Weeks Index (DHW)
One DHW is equivalent to one week of sea
surface temperatures one degree Celsius
warmer than the expected summertime
maximum. Two DHWs are equivalent
to two weeks at one degree above the
expected summertime maximum OR one
week of two degrees above the expected
D14
Source: Reference 1 of the introductory section references (see Section 11)
summertime maximum.
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