Climate change and coral reefs

June 27, 2001

Corals are famously sensitive to their environment, but their fate may be determined in the coming century by the relative rates and timing of sea level rise, global warming and other anthropogenic impacts. Disentangling these effects is a complex problem.

Corals can only grow within a very narrow window of ecological conditions, determined by depth, temperature and salinity. If sea levels rise more quickly than their slow growth can accommodate, they will die. They are also sensitive to predation and to marine pollution.

Coral reefs are in decline. Coral cover has shrunk by at least 30% in the last 30 years, and in some places (e.g., the Caribbean) by as much as 90%. Climatic stresses, such as cyclones, together with unusually warm ocean temperatures, high nutrient loads from soil erosion and fertilizers, are proving a lethal combination.

In 1997-98, unusually warm temperatures led to widespread coral bleaching and reef degradation worldwide, compounded by the fact that many reefs could not regenerate due to algal blooms created by high nutrient levels. Coral bleaching is predicted to rise as a result of continued global warming, while calcification rates will fall due to higher atmospheric concentrations of carbon dioxide (from fossil fuel burning).

However, the adaptability of coral reefs is often underestimated, says Malcolm McCulloch (Australian School of Earth Sciences, Canberra), who presents his research at Earth System processes, a multidisciplinary conference organised by the Geological Society of London (GSL) and the Geological Society of America (GSA).

"Looking back over longer timescales, we know that extreme variations in climate have occurred in the past" says McCulloch. "In only the last 500,000 years, we know that there were interglacial stages when conditions were warmer than today, and which persisted for longer. Multiple oscillations of sea level occurred during Marine Isotope Stage (MIS) 9 (c.320,000 years ago) and during the last interglacial, sea levels were between four and five metres higher than today. Coral growth during these periods was especially prolific, because the rising sea levels provided more space for corals to grow into, while the warmer oceans opened up larger areas to coral colonization.

"The problem that coral reefs face today is the two-pronged attack by anthropogenic pollution combined with global warming. The combined effects on the world's already highly stressed coral reefs may well be terminal.

"So in theory although warmer seas and rising sea levels could be good for corals - it's all a matter of timing. They could do well in a warmer world - as long as the rate of warming is no faster than they can cope with, and assuming they our pollution doesn't kill them off first".

During the Earth System Processes meeting, June 25-28, contact the GSA/GSL Newsroom at the Edinburgh International Conference Centre for assistance and to arrange for interviews: 44-131-519-4134

Ted Nield, GSL Science and Communications Officer
Ann Cairns, GSA Director of Communications

The abstract for this presentation is available at:

Post-meeting contact information:

Malcolm McCulloch
Research School of Earth Sciences
Australian National University
Canberra, Australia

Ted Nield
Geological Society of London

To view other Earth System Processes press releases, see

Geological Society of America

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