In discussions on the effects of climate change on coral reefs, the talk often turns to Australia's Great Barrier Reef (GBR), the world's largest barrier reef system. Some high-profile reports have forecast that, due to coral bleaching caused by climate change, the GBR could be severely threatened in coming decades. Most recently, a draft report by the Intergovernmental Panel on Climate Change - leaked to the media in January 2007 - said the GBR would become "functionally extinct" by 2050. (The leaked report was co-authored by Ove Hoegh-Guldberg at the University of Queensland, who has written other, similarly bleak forecasts concerning the GBR and climate change [see MPA News 6:8]).
Not all scientists agree with such forecasts for the GBR. Some people, in fact, have suggested that the GBR ecosystem might migrate southward along the coast of Australia, away from the warming waters. If such were the case, this could theoretically raise issues for the Great Barrier Reef Marine Park. If its habitats moved outside the current park boundaries, should the boundaries be moved in pursuit?
For insights on how the Great Barrier Reef Marine Park Authority (GBRMPA) views these scenarios, MPA News asked Johanna Johnson, project manager of the Climate Change Response Program for GBRMPA.
MPA News: Some scientists have forecast that, due to climate change, the Great Barrier Reef could be largely dead within the next few decades. Other people have suggested that the GBR will migrate southward as a result of climate change. Which of these scenarios do you expect is more likely?
Johanna Johnson: Impacts from climate change on the Great Barrier Reef, such as coral bleaching, are causing a decline in reef quality. Therefore the reef is likely to be very different in the next few decades, but not dead. This change will have implications for ecosystem function, how people perceive the reef, and the industries and communities that depend on it.
It is unlikely that reefs in general will migrate southward, as there is a decrease in shallow-water areas and an increase in siliceous sediments further from the equator, creating conditions that are less suitable for reef development. Although changes in climate may result in more suitable temperatures for coral growth away from the tropics, higher latitude marine environments tend to have substrata that are much less suited to development of carbonate reef structures. This means there is limited potential for a significant increase in reef development at higher latitudes. (Furthermore, the carbonate structures that provide the physical foundations for the Great Barrier Reef ecosystem have taken thousands of years to build. While some species may shift their distribution southward, it is unlikely that there would be any observable migration of GBR bioregions over human timeframes.)
The Great Barrier Reef Marine Park Authority expects its bioregions - reef and non-reef - to be increasingly challenged by climate-related stressors. The result will be a tendency for community dynamics to be increasingly dominated by recovery processes and an associated decrease in ecosystem quality, rather than to shift location. For these reasons, the GBRMPA is focusing its efforts on restoring and maintaining the ability of the ecosystem to cope with change - its resilience - rather than considering boundary changes.
For more information:
Johanna Johnson, GBRMPA, PO Box 1379, Townsville Qld 4810, Australia. Tel: +61 7 4750 0706; E-mail: j.johnson [at] gbrmpa.gov.au