Really worrying...Hard core data shows 14 per cent drop in coral growth on GBR since 1990
January 2, 2009
It’s official: the biggest and most robust corals on the Great Barrier Reef (GBR) have slowed their growth by more than 14 per cent since the "tipping point" year of 1990. Evidence is strong that the decline has been caused by a synergistic combination of rising sea surface temperatures and ocean acidification.
A paper* published today (Friday 2 January 2009) in the prestigious international journal Science and written by AIMS scientists Dr Glenn De’ath, Dr Janice Lough and Dr Katharina Fabricius is the most comprehensive study to date on calcification rates of 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 reported in the paper 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.
"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 and co-author Dr 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 per cent. However, by 2005 growth was declining by 1.5 per cent 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 and principal author Dr Glenn De’ath.
"The causes of this sharp decline remain unknown, but our study suggests that the combination of increasing temperature stress and ocean acidification may be diminishing the ability of GBR corals to deposit calcium carbonate," he said.