26 July 2010

An international team of scientists has been exploring Moreton Bay, close to Brisbane, as a possible ‘lifeboat’ to save corals from the Great Barrier Reef at risk of extermination under climate change.

In a new research paper they say that corals have been able to survive and flourish in the Bay, which lies well to the south of the main GBR coral zones, during about half of the past 7000 years.

Corals only cover about 1 per cent of the Moreton Bay area currently, and have clearly been adversely affected by clearing of the surrounding catchments and human activities on land and sea, said lead author Matt Lybolt, of the ARC Centre of Excellence for Coral Reef Studies and The University of Queensland.

“The demise of tropical coral reefs around the world is due mainly to overfishing, pollution and climate change," Mr Lybolt said.

"There is also plenty of historical evidence that coral reefs can move from one environment to another as the climate and other conditions change.”

“In view of this, various places – including Moreton Bay – are being investigated as possible refuges in which coral systems can be preserved should they begin to die out in their natural settings.

"Indeed, some people have even talked of relocating and re-seeding corals in other locations that better suit their climatic needs.”

The team’s study of Moreton Bay reveals that it is not exactly ideal coral habitat, being cold in winter, lacking sufficient direct sunlight, subject to turbid freshwater inflows and – more recently – to a range of human impacts.

“Even before European settlers came on the scene the Bay underwent phases in which corals grew prolifically – and phases in which they died away almost completely. We understand what causes corals to die back, but we are less clear about what causes them to recover,” Mr Lybolt said.

“Broadly, the corals seemed to do well at times when the climate, sea levels and other factors were most benign and stable – and to decline when El Nino and other disturbances made themselves felt.”

The Moreton Bay corals have been in an expansionary phase during the last 400 years, initially dominated by the branching Acropora corals but, since the Bay’s catchment was cleared and settled, these have died back leaving mainly slow-growing types of coral.

“Under climate change we expect winters to be warmer and sea levels to rise – and both of these factors will tend to favour the expansion of corals in Moreton Bay,” he said.

“However this expansion of corals may not occur unless we make a major effort to improve water quality in the Bay, by not allowing effluent, polluted runoff or sediment to enter it, and also by regrowing mangrove forests and seagrass beds within the Bay."

The team concluded that Moreton Bay’s potential as a good ‘lifeboat’ for corals was limited by four major factors:
• It is highly sensitive to what the 2 million residents of its catchment do that affects it
• It presently has very few branching corals left
• The area on which corals can grow is limited, both naturally and by human activity
• Finally, the historical record suggests the Bay is only a good coral refuge about half of the time.

Mr Lybolt said that there was nevertheless scope for changes in the management of the Bay and its surrounding catchments that could improve its suitability as a coral environment.

“The reefs of today don’t look anything like they did in the past, so it’s really a question of ‘What sort of coral reef do you want?’,” he said.

However, there needed to be a clearer scientific understanding of the drivers that caused corals to boom and bust within the Bay over the past seven millennia ensuring it was worthwhile attempting to make Moreton Bay a ‘lifeboat’ for the GBR, he said.

He said that there were very few suitable coral habitats south of the southern end of the GBR to which corals could migrate, should the northern parts of the reef become untenable for corals due to the impact of global warming.

Their paper “Instability in a marginal coral reef: the shift from natural variability to a human-dominated seascape” by Matt Lybolt, David Neil, Jian-xin Zhao, Yue-xing Feng, Ke-Fu Yu and John Pandolfi appears in the latest issue of the journal Frontiers in Ecology and Environment.

More information:
Matt Lybolt, CoECRS and UQ, ph +61 (0)7 3365 9001 or 0431 923 552
Professor John Pandolfi, CoECRS and UQ, +61 (0)7 3365 3050 or 0400 982 301.
Jenny Lappin, CoECRS, +61 (0)7 4781 4222
Jan King, UQ Communications Manager, +61 (0)7 3365 1120