#Status of Coral Reefs 2002 - International Coral Reef Action Network

Status of Coral Reefs of Australasia
LEARNING FROM 2002 GREAT BARRIER REEF BLEACHING EVENT
The vast extent of the 2002 high temperature anomaly on the Great Barrier Reef
(GBR) indicated by the NOAA 50km 2 hotspot maps prompted the Australian Institute
of Marine Science (AIMS) to use their high resolution SST data to guide site selection
in a large study of bleaching impact and survival. AIMS collated 3-day average satellite
sea surface temperature (SST) maps at 1km 2 resolution for the period December 2001
to March 2002. This enabled the identification of reefs in a 500,000km 2 area that had
been exposed to the greatest physical stress (i.e. highest temperature anomalies), for
field verification. Moreover with the maps, it was possible to select reefs in relatively
hotter and cooler reef waters (as controls), and select relatively hotter and cooler
habitats within hotter and cooler reefs as the pixel scale was 1 km 2 . Fieldwork was
conducted in June - July 2002 at 64 sites on 32 reefs from the central to the southern
Great Barrier Reef (over 1000km, from 1km from the coast, to 200km out in the
Coral Sea).
In the coolest water patches, there were no reefs with damage from coral bleaching at
any site or any depth. However, in the hottest water patches, there was significant
coral mortality from bleaching with some unusual patterns. Some ubiquitous hard
corals that were considered to be the most sensitive (e.g. family Pocilloporidae)
survived well, where others (Acroporidae and Faviidae) had suffered significant levels
of injury and mortality. Within ubiquitous genera, there was range of sensitivities (e.g.
Acropora and Porites) with some showing little mortality. Many coral species that
normally have low stored energy reserves (e.g. Acropora, Montipora) were still alive or
white in mid-winter (when temperatures were 20°C plus or minus a few degrees)
suggesting they were obtaining their nutrition from capturing food from the water
(heterotrophic nutrition). These results indicate that there are more heat tolerant
corals that may increase in abundance to replace losses of the more sensitive species
in coming decades. There was also local variability in bleaching and mortality within
reefs that may be related to the local shape of the reef and variations in currents.
Selected species are being examined to determine if there are genetic markers in the
symbiotic algae (zooxanthellae) that code for greater heat tolerance. The final goal is
to identify reefs with more resistance to bleaching as these should be the focus for
coral reef MPA planning around the world. The study was conducted with support
from the Nature Conservancy and the David and Lucille Packard Foundation. From:
Terry Done, Australian Institute of Marine Science,
by habitat loss, particularly the die-off of inshore seagrasses after flooding, drowning in set
gillnets, boat strikes and indigenous hunting. Pressures on turtle populations in Australian
waters include trawl and shark nets, traditional hunting, floating rubbish and boat-strikes,
as well as habitat loss and destruction of nests by feral pigs and foxes. While there is strong
protection for turtles in Australian waters, these animals often migrate thousands of
kilometres to areas where they are hunted and nests are emptied.
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