The Great Barrier Reef Has Been Hiding Another Massive Reef

The iconic coral reef sits above an even deeper one

LiDAR imaging of the bioherms beyond the Great Barrier Reef, which is marked in red. Australian Hydrographic Service

For decades, scientists studying Australia’s Great Barrier Reef have been stumped by hints of large geologic structures hiding in the deep waters nearby. But thanks to a recent seafloor mapping project by the Royal Australian Navy, they have finally discovered what has long been lying beneath the iconic reef: a deeper, massive reef.

“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,” Robin Beaman, a marine geologist at James Cook University, says in a statement.

The unusual, doughnut-shaped mounds have long puzzled researchers, but until now they have not had the equipment to study it properly. Using LiDAR, which uses lasers instead of radio waves to create radar images, naval aircraft scanned the waters around the Barrier Reef. In the process of creating the highest-resolution maps of the region to date, the scanners also revealed that the deep-sea reef stretches across more than 2,000 square miles, Daniel Oberhaus writes for Motherboard.

“That’s three times the previously estimated size, spanning from the Torres Strait to just north of Port Douglas,” Queensland University of Technology researcher Mardi McNeil says in a statement. “They clearly form a significant inter-reef habitat, which covers an area greater than the adjacent coral reefs.”

Unlike the more famous Great Barrier Reef, which is made up of coral, this new reef is formed from a common kind of green algae called Halimeda. When these algae die, they form small flakes of limestone that can quickly build up into massive structures called “bioherms,” Bec Crew reports for ScienceAlert. While these organisms are fairly common in Australian waters, the newly-identified reef raises questions about how its ecosystem interacts with the shallower Barrier Reef, as well as how it is doing in the face of climate change.

“As a calcifying organism, Halimeda may be susceptible to ocean acidification and warming,” Jody Webster, a climatologist and geologist at the University of Sydney, says in a statement. “Have the Halimeda bioherms been impacted, and if so to what extent?”

When it comes to the Great Barrier Reef, scientists have decades of research to look back on to see how rapidly the fragile ecosystem is changing. However, this is only the first step towards beginning to understand this deeper reef. By studying these giant structures, scientists hope to get a better sense of how what life it supports and how the two reefs interact, as well as how the local oceanic ecosystem has changed in the last few millennia.

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