SYDNEY: Ocean acidification and rising temperatures are gradually killing off the biggest and most robust corals on the Great Barrier Reef since 1990, the "tipping point" year, says a new study.
The study, authored by Australian Institute of Marine Science (AIMS) scientists Glenn De'ath, Janice Lough and Katharina Fabricius, is the most comprehensive one to date on calcification rates of Great Barrier Reef (GBR) corals.
Calcification is how much skeleton the coral puts down each year. Reef corals create their hard skeletons from materials dissolved in seawater. When large amounts of atmospheric carbon dioxide enter seawater, the resulting chemical changes effectively reduce the ability of marine organisms to form skeletons.
The findings are based on rigorous statistical analyses of annual growth bands from 328 Porites corals from 69 reefs across the length and breadth of the GBR, and extending back in time up to 400 years.
The data are from AIMS Coral Core Archive (ACCA), the most extensive such collection in the world, said an AIMS release.
"It is cause for extreme concern that such changes are already evident, with the relatively modest climate changes observed to date, in the world's best protected and managed coral reef ecosystem," according to AIMS scientist Janice Lough.
Up to the tipping point in 1990, there were modest fluctuations in calcification, with an annual decline rate recorded that year of 0.3 percent.
However, by 2005 growth was declining by 1.5 percent per year. On current trends, the corals would stop growing altogether by 2050.
"The data suggest that this severe and sudden decline in calcification is unprecedented in at least 400 years," said AIMS scientist Glenn De'ath.
"Coral skeletons form the backbone of reef ecosystems.Their complexity provides the habitat for the tens of thousands of plant and animal species associated with the reef," said Fabricius said.
These findings were published in Science.
