The magnificent coral reefs and lagoon of Lord Howe island is the most southern coral in the world and may well be the last bastion of coral reefs threatened inexorably by global warming in other places. Water temperatures of 26 degrees celcius are enough to bring on coral bleaching and Lord Howe has not been immune to such events. bdimages

By BRIDIE SMITH
March 25, 2010 THE world’s southernmost coral reef is on a knife edge, according to scientists who say this summer’s above-average water temperatures have left Lord Howe Island’s unique reef stressed and bleached. In parts of the reef, especially areas around the island’s lagoon, up to 95 per cent of corals have been bleached since January. ”This is a significant bleaching event,” said Peter Harrison, director of marine studies at Southern Cross University, who has been monitoring the reef since 1993. Professor Harrison said the situation, caused by warmer-than-usual waters carried south by the currents from the Great Barrier Reef, had been compounded by a period of light winds and little cloud cover. ”That means both increased temperature and increased light penetration into the water, which stressed the symbiotic algae which lives in the corals,” he said. It is the first major bleaching of the reef, which is considered globally significant because of its unique combination of tropical, subtropical and temperate species. Professor Harrison said the bleaching was significant for another reason. This, he said, was evidence that subtropical areas were not immune to the impact of climate change. ”It is a clear warning that changes to climate will impact not only the tropical coral systems but also the subtropical ones,” he said. … In 1998 Professor Harrison said the maximum temperature recorded in the island’s lagoon was just over 27 degrees. This year it passed 28 degrees, more than two degrees above normal summer water temperatures. …

Coral reef on Lord Howe bleached by summer