Lurking in the deeper seafloor behind the familiar coral reefs was an astounding discovery.

New Reef Under Great Barrier Reef
Credit: Fairfax Media via Getty Images

Australia’s Great Barrier Reef has been hiding what scientists have discovered to be a massive reef in its nearby waters.

Scientists from James Cook University, the University of Sydney, and Queensland University of Technology utilized laser data via a naval aircraft to track down over 6,000 square kilometers of fields hosting donut-shaped circular mounds hidden in plain sight.

“That’s three times the previously estimated size, spanning from the Torres Strait to just north of Port Douglas,” said Mardi McNeil, a lead author of the research from the Queensland University of Technology, in a news release on the discovery.

The mounds, with are roughly 200-300 meters in width and 10 meters deep at their center, are geological structures formed by a type of green algae known as Halimeda.

There's a giant reef hidden next to Australia's Great Barrier Reef.
Credit: James Cook University

When the algae die, they form small limestone flakes, which eventually form into these mounds, which are known as bioherms.

“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 Dr. Robin Beaman of James Cook University, in a statement.

The new revelation brings increased urgency to addressing the area’s vulnerability to climate change, as rising ocean temperatures and increased acidification in the waters may impact the algae.

According to Beaman, the discovery has paved the way for potential new research in the area that could include sediment coring, conducting sub-surface geophysical surveys, and utilizing autonomous underwater technology to learn more about the physical and biological functioning of these submerged structures.

Talia Avakian is a digital reporter at Travel + Leisure. Follow her on Twitter at @TaliaAvak.