Expansive Reef Found Behind the Great Barrier Reef

High-resolution seafloor imaging revealed a much larger network of reef-like structures off the Australian coast than previously thought.

Sep 6, 2016
Ben Andrew Henry


Australian scientists have discovered vast fields of donut-shaped, reef-like structures known as bioherms stretching behind and around the Great Barrier Reef. “We’ve now mapped over 6,000 square kilometers. That’s three times the previously estimated size, spanning from the Torres Strait to just north of Port Douglas,” said Mardi McNeil of Queensland University of Technology in a statement. “They clearly form a significant inter-reef habitat which covers an area greater than the adjacent coral reefs.”

Bioherms are formed by the calcium carbonate remains of a common green algae that has a calcified stem. The white, pebble-size flakes gradually accumulate into circular mounds on the sea floor. A single mound can span as much as 300 meters across and reach 10 meters deep at the center. Scientists first observed the fields of bioherms behind the Great Barrier Reef in the 1970s, but had never attempted to image their whole extent, the press release states.

The team of Australian scientists worked in cooperation with the Royal Australian Navy to fly LiDAR-equipped aircraft over the bioherm fields and produce detailed scans of the ocean floor. The team published their findings in Coral Reefs last month (August 24). “The deeper seafloor behind the familiar coral reefs amazed us,” said coauthor Robin Beaman of James Cook University in the statement.

The authors expressed concern that the calcium-based bioherms could be vulnerable to ocean acidification caused by climate change. Beaman also noted that sediment cores from the thick bioherms could be rich sources of geological information. “What do the 10-20 meter 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?”