TOWNSVILLE, Australia (CNN) --The world's largest living organism, Australia's Great Barrier Reef, is under threat from rising sea temperatures which threaten to kill off the colorful corals which form the reef.

The 2,000 kilometer (1,400 miles) reef off the east coast of northern Australia is a major tourist destination attracting tens of thousands of international tourists each year.

But according to research by the Australian Institute of Marine Science, water temperatures last southern summer were the warmest on record.

This phenomenon -- believed to be related to global warming -- combined with this year's El Nino weather pattern means the fragile coral could struggle to survive.

While sea temperatures around the reef have not risen greatly over the past century -- about half a degree Celsius -- the coral have a very low tolerance factor of only one or two degrees.

The Australian institute 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.

"Unless the corals can adapt and become acclimatized then obviously the long-term future for the coral is at risk," oceanographer Craig Steinberg told Reuters.

"The outlook isn't good. If coral can't adapt then they're going to bleach and you get mass mortality."

AIMS researchers are now 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 there is no indication of any short-term ability to acclimatize.

Some scientists believe global warming is already responsible for the destruction of coral reefs around the Pacific island nation of Fiji.

The Great Barrier Reef is a World Heritage listed site and considered one of the world's greatest natural wonders.

The bleaching threat comes as the Australian government on Thursday took other action to protect the reef, releasing plans to restrict shipping movements around the area.

The move comes more than a year after a Malaysian container ship ran aground on the reef causing physical damage to the coral and also polluting the surrounding waters.

Key changes could include making pilots compulsory for ships travelling the Torres Strait region near the northern end of the reef and the removal of "preferred routes" for shipping through the Whitsundays Island region to the south.

© 2002 Cable News Network LP, LLLP

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