Collapse of the corals, which was due to agricultural run-off, was first noted between the 1920s and 1950s. According to New Scientist
, strong storms can damage and kill the corals, but the nutrients from the run-off allows seaweed to move into the corals, preventing coral from regenerating.
University of Queensland scientist, Dr George Roff, told EScience News
"Corals have always died from natural events such as floods and cyclones, but historically have shown rapid recovery following disturbance. [Studies] suggest that the chronic influence of European settlement on the Queensland coastline may have reduced the corals ability to bounce back from these natural disturbances."
Scientist began observing and studying the coral again in the 1980's. A group of University of Queensland researchers began drilling sediment cores, 6.5 to 16.5 feet long, from the seafloor at Pelorus Island. They were able to reconstruct the history of the reef and found that the same deterioration and collapse which had occurred previously is happening again. Since 1985, nearly half of the previously observed coral has vanished. Researchers believe that rate is likely continue if immediate countermeasures are not put into place.
University of North Carolina Chapel Hill marine biology professor, John Bruno, told ZME Science
“In 2007, we first sounded the alarm that the Great Barrier Reef, and Pacific reefs in general, were not as pristine and resilient as a lot of people wanted to believe. But still, this is really shocking to me.”
The recent study, which was conducted by the Australian Institute of Marine Science
(AIMS) and the University of Wollongong, showed that the Great Barrier Reef has lost half its coral cover over the last 27 years. The majority of the coral loss is in more shallow waters. The study showed that coral at depths of 30 meters or more remains relatively healthy.
Pim Bongaerts, a University of Queensland professor, told CNN
"We have found their deep reef zone is hardly disturbed at all. In fact the most striking thing is the abundance of coral on the deep reef. What has blown me away is to see that even 70 to 80 meters down, there are significant coral populations."