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Great Barrier Reef threatened
25/07/2002 11:32 - (SA)
Michael Christie
Sydney - Sea temperatures at Australia's Great Barrier Reef last summer were the warmest on record and this year's El Nino event means the risk of mass coral bleaching has increased considerably, scientists reported on Thursday.
The Australian Institute of Marine Science (AIMS) has just completed an atlas of sea temperatures over the past decade and amalgamated it with historical data to show 2002 was the warmest year for water temperatures off northeast Australia since 1870.
The rise in temperatures around the world's largest living organism coincided with mass bleaching earlier this year that affected around 60 percent of the Great Barrier Reef's 345 400 square km (133 300 square miles) of coral.
"Unless the corals can adapt and become acclimatised then obviously the long-term future for the coral is at risk," said AIMS oceanographer Craig Steinberg.
"The outlook isn't good. If coral can't adapt then they're going to bleach and you get mass mortality."
The sea temperature over the last century has risen by just half a degree Celsius.
But corals tend to live within one to two degrees of their maximum temperature threshold and a tiny increase is therefore enough to ensure a major impact.
Bleaching occurs when coral becomes stressed. It involves a breakdown in the symbiotic relationship between the coral and algae and in severe cases the coral will die.
The last time the reef's coral bleached because of higher than normal temperatures was in 1998, when the El Nino weather phenomenon warmed the waters of the Pacific, bringing drought to eastern Australia and floods to parts of Latin America.
Global warming
Last year was not an El Nino year, making the high temperatures even more unusual and meaning they were almost certainly a by-product of pollution-induced global warming, said AIMS climate expert Janice Lough.
The onset of another El Nino this year, albeit one that US experts say is likely to be mild, has increased the chances of another southern hemisphere summer of high sea water temperatures at the start of 2003.
"We've changed the baseline. It is a worry," Lough from Townsville in the far north of Queensland state.
Coral can recover after mild bleaching.
But researchers fear that its ability to overcome heat stress may be weakened as high temperatures become more common.
AIMS researchers are trying to establish whether coral has the ability to adapt quickly to changing temperatures.
There is evidence that they can over long periods of time, but so far no indication of any short-term ability to acclimatise.
In the meantime, there is not a lot that can be done to protect the Great Barrier Reef - one of Australia's main tourist attractions and a World Heritage site.
"Reef managers can do all they can to reduce all the other threats to coral reefs but they can't solve individually the global problem (of climate change)," said Lough.
"It's not so much that the reef will die, it's that the reef will change," she said. "If you sort of knock out certain of the corals then other organisms might take their place."
- Reuters
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