Researchers have found that seaweed is outcompeting coral in some parts of the Great Barrier Reef, which is home to vast numbers of marine species including turtles.
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SYDNEY: Australian natural wonder the Great Barrier Reef is overgrown in places by seaweed in what could be a worrying indication of the health of the coral structure, scientists said on Wednesday.
Surveys of the World Heritage-listed reef, already at risk from global warming, found that more than 40 % of areas closest to shore were dominated by the green weed. The research is published in the journal Marine Ecology Progress.
Choked with weed
"We knew there would be some weed there, we were just surprised how much," said David Bellwood, a marine biologist from James Cook University in Townsville, Queensland. "We are concerned about it because it does look like a lot of weed and in other places in the world, weed is an indication of decline."
Bellwood said the offshore reefs, those at least 20 km from Australia's eastern coast, were largely untouched by the algae but that some of those closer to shore were choking with weed.
While the reason for the build-up of greenery was not known, he said he suspected it was because algae-eating fish have died out in those areas.
Other researchers have previously suspected that ocean acidification may make it difficult for corals to compete with seaweed in the reef (see "Oceans of acid").
Little red light
"The question is, does this mean the Barrier Reef is in real trouble? That the reef is rotting from the inside out? Or does it mean to say that that amount of weed is natural? And the answer is: it's hard to say," he said.
Bellwood, from the Centre of Excellence for Coral Reef Studies, said the best defence for the reef would be clean water and the existence of herbivorous fish which could graze on the weeds.
"The Great Barrier Reef is in the best condition of any reef in the world," he said. "However, it is suffering. And it has suffered significant declines in coral cover in the last few years. The presence of that weed is just another little red light."
