Lidar mapping of Great Barrier Reef reveals separate vast reef

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Using lidar technology, scientists in Australia and the UK have discovered a coral reef spanning more than 6,000km behind the Great Barrier Reef.

The high-resolution seafloor data obtained by lidar-equipped aircraft belonging to the Royal Australian Navy revealed great fields of unusual doughnut-shaped circular mounds, which could help marine geologists better understand how global warming is affecting underwater ecosystems.  

The scientists from James Cook University (JCU) in the UK, the University of Sydney and the Queensland University of Technology mapped more than 6,000 square kilometres of the newly-discovered reef, which sits much deeper than the Great Barrier Reef and is three times larger than scientists previously estimated it to be.  

‘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 JCU’s Dr Robin Beaman. ‘The deeper seafloor behind the familiar [Great Barrier] coral reefs amazed us.’

The fields of circular doughnut-shaped rings are Halimeda bioherms, large reef-like geological structures formed by the growth of a green algae called Halimeda that have living calcified segments. These leave small limestone flakes when the algae die, which over time build up into large reef-like mounds, or bioherms.

Marine geologists previously understood these bioherms to form linear, dune-like parallel ridges and troughs, quite different to the complex seafloor now revealed with the benefit of lidar and multibeam swath bathymetry data collected in the past few years.

The revelations about the extent of the bioherm field make questions over its vulnerability to climate change even more pressing, commented Jody Webster, UTS associate professor: ‘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?’

The discovery has also opened up many other new avenues of research, Dr Beaman added:  ‘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 timescale?’

He said future research would require sediment coring, sub-surface geophysical surveys, and employing autonomous underwater vehicle technologies to unravel the physical, chemical and biological processes of the structures.

Further information

Paper, ‘New constraints on the spatial distribution and morphology of the Halimeda bioherms of the Great Barrier Reef, Australia’ in Coral reefs