Scientists have discovered a vast reef behind the familiar Great Barrier Reef, unveiling great fields of unusual donut-shaped circular mounds, each 200-300 metres across and up to 10 metres deep.
Scientists from the University of Sydney and Queensland University of Technology worked with high-resolution seafloor data provided by LiDAR-equipped aircraft.
“We’ve known about these geological structures in the northern Great Barrier Reef since the 1970s and 80s, but never before has the true nature of their shape, size and vast scale been revealed,” said Robin Beaman from James Cook University.
“The deeper seafloor behind the familiar coral reefs amazed us,” said Beaman, calling it an astounding revelation.
The fields of circular donut-shaped rings are Halimeda bioherms, large reef-like geological structures formed by the growth of Halimeda, a common green algae composed of living calcified segments.
These form small limestone flakes on death, looking much like white cornflakes. Over time these flakes build up into large reef-like mounds, or bioherms.
Mardi McNeil from Queensland University of Technology said their extent is vast.
“We’ve now mapped over 6,000 square kilometres. That’s three times the previously estimated size, spanning from the Torres Strait to just north of Port Douglas,” said McNeil.
“They clearly form a significant inter-reef habitat which covers an area greater than the adjacent coral reefs,” McNeil said.
Associate Professor Jody Webster from the University of Sydney, said the revelations about the extent of the bioherm field make questions over its vulnerability to climate change even more pressing.
“As a calcifying organism, Halimeda may be susceptible to ocean acidification and warming. Have the Halimeda bioherms been impacted, and if so to what extent?”
Beaman said the discovery also opened up many other new avenues of research.
“For instance, what do the 10-20 metre thick sediments of the bioherms tell us about past climate and environmental change on the Great Barrier Reef over this 10,000 year time-scale?” he said.