TL: CORAL BLEACHING BACKGROUND
SO: GREENPEACE AUSTRALIA (GP)
DT: APRIL, 1998

WHAT IS CORAL BLEACHING?

Coral bleaching occurs as a result of the microscopic algae
which live in symbiosis within the coral tissue - zooxanthellae
- being expelled from the tissue as a result of ecological
stress. A variety of stresses can produce this effect, including
hot water, cold water, excessive UV radiation, or pollution.

When coral becomes stressed, this algae is expelled causing the
coral to turn white or "bleach". The coral's colour and most of
its food come from these algae, so without them the coral cannot
grow. Coral bleaching can kill corals and after particularly
severe episodes coral reefs may take decades to recover.

Beyond directly killing coral, bleaching can have indirect
effects of reef ecosystems. After the severe bleaching off
Panama and Galapagos in 1982/83, large areas of dead coral have
become colonised by bottom algae, which in turn support
increased populations of sea urchins. Sea urchins scrape the
coral surface of the reef as they feed, contributing to the
erosion of the reef structure and prolonging, or even
preventing, their recovery.

Whilst corals are stressed by pollution and sedimentation, they
have indicated their particular sensitivity to sudden sea
temperature  changes. They thrive in waters up to 28 degrees
Celsius, but if exposed to temperatures just 1 degree Celcius
higher - even for two or three days - the algae are expelled
from the coral.

WHAT IS THE LINK BETWEEN CORAL BLEACHING AND CLIMATE CHANGE?

"Projected increases in seawater temperatures...appear to be a
major threat to coral reefs." Intergovernmental Panel on Climate
Change.

Corals will inevitably be among the first organisms to show the
consequences of a sustained increase in global temperatures,
because of the fragile temperature dependence of the tiny algae
which live in the coral's cells. 

Global temperatures have risen over the last century and the
last two decades have seen the hottest years this century. The
United Nation's Intergovernmental Panel on Climate Change (IPCC)
has concluded greenhouse gas emissions appear to be partly
responsible for this increase and that "the balance of evidence
suggests a discernible human influence on global climate".

American coral experts Thomas Goreau and Raymond Hayes have
shown that coral bleaching events have become more frequent,
widespread and severe since the early 1980s. Major bleaching
events have occurred in all the major reef communities,
including Australia, China, Japan, Panama, Thailand, Malaysia,
the Philippines, India, Indonesia, Kenya, the Red Sea, Puerto
Rico, Jamaica, the Bahamas and Okinawa.

The IPCC has concluded that the unprecedented extent and
severity of coral bleaching over the last two decades is
consistent with measured sea temperature increases and increases
confidence in direct temperature observations of global warming.

Researchers express concern about the future of reef ecosystems
if episodic high temperature stress continues:

"Increased mass coral bleaching would seriously impact marine
biodiversity, fisheries, tourism, on-shore protection, and the
ability to adapt to rising sea level in the over 100 countries
where coral reefs are major natural and economic resources."
Thomas Goreau and Raymond Hayes, American coral experts.

"Sea warming over a period of 50 or less years may cause the 
extinction of many coral species." Peter Glynn, University of
Miami.

"[it is] extremely unlikely that the majority of coral reef
organisms will be able to evolve quickly enough to keep pace
with the predicted changes in sea temperature." Ove Hoegh-
Guldberg, from the University of Sydney

" ...if the temperature increase of one or two degrees C,
predicted by the Intergovernmental Panel on Climate Change, does
take place over the next 50 years in the tropical latitudes, the
consequences for coral reefs could be disastrous. Unlike the
miners with the canary, we cannot yet link bleaching to a clear
cause. But this does not mean we should ignore the coral's
message." Barbara Brown, University of Newcastle and John Ogden,
University of South Florida

THE GREAT BARRIER REEF: A VICTIM OF A GLOBAL PHENOMENON

"Australia's coral reefs, including the Great Barrier Reef, are
among the region's most sensitive environments to sea-level and
climate change..."  Intergovernmental Panel on Climate Change.

"Australia's Great Barrier Reef and other coral reefs are
vulnerable to temperature-induced bleaching and death of corals,
in addition to sea-level rise and weather changes."
Intergovernmental Panel on Climate Change. 

Australia has the largest area of coral reefs in the world.
These reefs are extremely diverse and harbour a number of
endangered species. The Great Barrier Reef, which stretches from
the tip of northern Queensland to Bundaberg on Australia's
eastern coast, has been given World Heritage status and is
considered on of the seven wonders of the natural world.

Coral bleaching events on the Great Barrier Reef have been
recorded in 1980, 1982, 1987, 1992 1994, and 1998. According to
the Great Barrier Reef Marine Park Authority (GBRMPA), the mass
bleaching on the Great Barrier Reef this year is likely to
surpass the worst previous event in 1982. The main reason for
the bleaching appears to abnormally high sea temperatures,
however, run-off from heavy rainfall and high levels of UV
radiation caused by clear skies also appear to played a part.

One of the best records of recurrent bleaching events on the
Great Barrier Reef comes from the inshore fringing reefs of
Magnetic Island, a continental island situated around 8km north
of Townsville, Queensland, Australia. Researchers have observed
bleaching in January/February period of 1979/80, 1981/82,
1986/87, 1993/94 and this year. Researchers have concluded that
bleaching on Magnetic Island appears to be related to abnormally
high temperatures (heatwaves) during summer months.

Annual air temperatures around Townsville have increased by
nearly 1 degree C since 1942. Other records across Queensland
also show increases in temperature. Temperatures similar to
those present during bleaching events at Magnetic Island in
recent years have not otherwise been recorded in the local area
since the 1930s. Scientists from the University of Sydney and
the Great Barrier Reef Marine Park Authority have concluded
that:
"The relationship between bleaching events and periods of
elevated  air and seawater temperatures and the absence of
similar temperatures  from the late 1930s until the late 1980s,
is suggestive that  bleaching events at Magnetic Island are
comparatively recent  phenomenon _ and are associated with a
change in the local climate system."

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