Reef cycles investigated
Researchers have mapped the death and rebirth of the Great Barrier Reef.
An international study of the Great Barrier Reef has shown that in the past 30,000 years the world’s largest reef system has suffered five death events, largely driven by changes in sea level and associated environmental change.
Over millennia, the reef has adapted to sudden changes in environment by migrating across the sea floor as the oceans rose and fell.
It is the first such study to reconstruct the evolution of the reef over the past 30 millennia in response to major, abrupt environmental change.
The 10-year, multinational effort has shown the reef is more resilient to major environmental changes such as sea-level rise and sea-temperature change than previously thought, but also showed a high sensitivity to increased sediment input and poor water quality.
Associate Professor Jody Webster from the University of Sydney says it remains an open question as to whether its resilience will be enough for it to survive the current worldwide decline of coral reefs.
“Our study shows the reef has been able to bounce back from past death events during the last glaciation and deglaciation,” he said.
“However, we found it is also highly sensitive to increased sediment input, which is of concern given current land-use practices.”
The study used data from geomorphic, sedimentological, biological and dating information from fossil reef cores at 16 sites at Cairns and Mackay.
The study covers the period from before the “Last Glacial Maximum” about 20,000 years ago when sea levels were 118 metres below current levels.
The final reef-death event about 10,000 years ago, from before the emergence of the modern reef about 9000 years ago, was not associated with any known abrupt sea-level rise or “meltwater pulse” during the deglaciation.
Rather it appears to be associated with a massive sediment increase and reduced water quality alongside a general rise in sea level.
The authors propose that the reef has been able to re-establish itself over time due to continuity of reef habitats with corals and coralline-algae and the reef’s ability to migrate laterally at between 0.2 and 1.5 metres a year.
However, Associate Professor Webster said it was unlikely that this rate would be enough to survive current rates of sea surface temperature rises, sharp declines in coral coverage, year-on-year coral bleaching or decreases in water quality and increased sediment flux since European settlement.