Climate Change, Coral Bleaching and the Future of the World's Coral Reefs
CLIMATE
CHANGE
CORAL
BLEACHING
and the
FUTURE
of the
WORLDÕS
CORAL
REEFS
by
O V E H O E G H Ð G U L D B E R G
ASSOCIATE PROFESSOR,
SCHOOL OF BIOLOGICAL SCIENCES,
UNIVERSITY OF SYDNEY
DIRECTOR,
THE CORAL REEF RESEARCH INSTITUTE,
UNIVERSITY OF SYDNEY
ISBN 90-73361-52-4
Sea temperatures in the tropics have increased by almost
1oC over the past 100 years and are currently increasing at the rate of approximately 1-2oC per century. Reefbuilding corals, which are central to healthy coral reefs, are currently living close to their upper thermal limit.
They become stressed if exposed to small slight increases
(1-2oC) in water temperature and experience coral bleaching. Coral bleaching occurs when the photosynthetic symbionts of corals (zooxanthellae) become increasing vulnerable to damage by light at higher than normal temperatures. The resulting damage leads to the expulsion of these important organisms from the coral host. Corals tend to die in great numbers immediately following coral bleaching events, which may stretch across thousands of square kilometers of ocean. Bleaching events in 1998, the worst on record, saw the complete loss of live coral from reefs in some parts of the world.
This paper reviews our understanding of coral bleaching and demonstrates that the current increase in the intensity and extent of coral bleaching is due to increasing sea temperature. Importantly, this paper uses the output from four different runs from two major global climate models to project how the frequency and intensity of bleaching events are likely to change over the next hundred years if greenhouse gas emissions are not reduced. The results of this analysis are startling and a matter of great concern.
Sea temperatures calculated by all model projections show that the thermal tolerances of reef-building corals are likely to be exceeded within the next few decades. As a result of these increases, bleaching events are set to
CHANGE
CORAL
BLEACHING
and the
FUTURE
of the
WORLDÕS
CORAL
REEFS
by
O V E H O E G H Ð G U L D B E R G
ASSOCIATE PROFESSOR,
SCHOOL OF BIOLOGICAL SCIENCES,
UNIVERSITY OF SYDNEY
DIRECTOR,
THE CORAL REEF RESEARCH INSTITUTE,
UNIVERSITY OF SYDNEY
ISBN 90-73361-52-4
Sea temperatures in the tropics have increased by almost
1oC over the past 100 years and are currently increasing at the rate of approximately 1-2oC per century. Reefbuilding corals, which are central to healthy coral reefs, are currently living close to their upper thermal limit.
They become stressed if exposed to small slight increases
(1-2oC) in water temperature and experience coral bleaching. Coral bleaching occurs when the photosynthetic symbionts of corals (zooxanthellae) become increasing vulnerable to damage by light at higher than normal temperatures. The resulting damage leads to the expulsion of these important organisms from the coral host. Corals tend to die in great numbers immediately following coral bleaching events, which may stretch across thousands of square kilometers of ocean. Bleaching events in 1998, the worst on record, saw the complete loss of live coral from reefs in some parts of the world.
This paper reviews our understanding of coral bleaching and demonstrates that the current increase in the intensity and extent of coral bleaching is due to increasing sea temperature. Importantly, this paper uses the output from four different runs from two major global climate models to project how the frequency and intensity of bleaching events are likely to change over the next hundred years if greenhouse gas emissions are not reduced. The results of this analysis are startling and a matter of great concern.
Sea temperatures calculated by all model projections show that the thermal tolerances of reef-building corals are likely to be exceeded within the next few decades. As a result of these increases, bleaching events are set to
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