An Early Eco Disaster at the Great Barrier Reef.
The Great Barrier Reef is the world's largest coral reef system composed of over 2,900 individual reefs and 900 islands stretching for over 1,600 miles over an area of approximately 133,000 sq miles. The reef is located in the Coral Sea, off the coast of Queensland, Australia. It is a fragile and immense ecosystem subject to continuing and increasing man made exposure hazards. Australian marine scientists have unearthed evidence of an historic coral collapse in Queenslandâ€™s Palm Islands following human development on the nearby mainland. Cores taken through the coral reef at Pelorus Island confirm a healthy community of branching Acropora corals flourished for centuries before European settlement of the area, despite frequent floods and cyclone events. Then, between 1920 and 1955, the branching Acropora failed to recover.
Scientists from the ARC Centre of Excellence for Coral Reef Studies at the University of Queensland say the rapid collapse of the coral community is potential evidence of the link between man-made changes in water quality and the loss of corals on the Great Barrier Reef.
It adds weight to evidence that human activity is implicated in the recent loss of up to half of the corals on the Great Barrier Reef, says Professor John Pandolfi of CoECRS and UQ.
The destruction of branching corals coincided with wide-spread land clearing for grazing and agriculture which took place in the nearby Burdekin River catchment in the late 19th Century, causing an increase in the amount of mud and nutrients into the GBR lagoon, says the lead author of a new study on the collapse, Dr George Roff, of CoECRS and UQ.
"Corals have always died from natural events such as floods and cyclones, but historically have shown rapid recovery following disturbance. Our results 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" he says.
The Great Barrier Reef's environmental pressures include lowered water quality from runoff including suspended sediment, excess nutrients, pesticides, and fluctuations in salinity. The effects of climate change, including increased temperatures, storms and coral bleaching. Cyclic outbreaks of the crown-of-thorns starfish, overfishing which disrupts food chains, and shipping routes which can result in oil spills or improper ballast discharge also damage to the reef.
The team took cores from dead coral beds on the western side of Pelorus Island and then analysed their coral species composition and their age, using high-precision uranium dating methods pioneered by a team lead by one of the studyâ€™s co-authors, Jian-xin Zhao at the University of Queenslandâ€™s Radio Isotope Facility. They then aligned this with records of cyclones, floods and sea surface temperatures over the same period.
"Our results imply a previously undetected historical collapse in coral communities coinciding with increased sediment and nutrient loading following European settlement of the Queensland coastline," the researchers report in their paper.
"And, even more significantly, we found no similar collapse occurring at any time in the previous 1700 years covered by our cores. Throughout this period the branching corals continued to flourish â€“ despite all the cyclones and natural impacts they endured."
At two sites the Acropora corals vanished completely while at a third there was a marked shift in coral species from Acropora to Pavona, which the researchers say parallels similar observations of human impacts in the Caribbean.
"On a global scale, our results are consistent with a recent report from the Caribbean region, where land use changes prior to 1960 were implicated in a significant decline in Acropora corals in near-shore reefs."
The research has raised another realistic possibility â€“ that current coral surveys may significantly underestimate the possibility of major unseen shifts such as these having taken place in the period before effective coral records began, the researchers suggest.
Their paper "Palaeoecological evidence of a historical collapse of corals at Pelorus Island, inshore Great Barrier Reef, following European settlement" appears in the latest issue of Proceedings of the Royal Society B.
For further information see Early Collapse.
Map image via Wikipedia.