A team of researchers from James Cook University, University of Sydney and Queensland University of Technology found a massive reef behind the Great Barrier Reef. They found vast fields of donut-shaped Halimeda bioherms mounds, which measure between 200 and 300 meters wide and 10 meters deep.

Halimeda bioherms are big, reef-like circular geological structures created by the growth of common green algae called Halimeda. The algae are composed of living calcified segments, forming small limestone flakes that the researchers liken to white cornflakes. These limestone flakes grow into massive reef-like mounds, which are also called bioherms.

The researchers analyzed laser data from the Royal Australian Navy. According to JCU’s Robin Beaman, these donut-shaped circular mounds have been known since the 1970s and 1980s but previous researchers were not able to determine their scale, size and shape.

“We’ve now mapped over 6,000 square kilometers,” says the study’s lead author Mardi McNeil of Queensland University of Technology. “That’s three times the previously estimated size, spanning from the Torres Strait to just north of Port Douglas. They clearly form a significant inter-reef habitat which covers an area greater than the adjacent coral reefs.”

Jody Webster, an associate professor from the University of Sydney, points out that the Halimeda could be vulnerable to ocean acidification and warming. As of now, the extent of these environmental changes on Halimeda bioherms cannot be determined.

Beaman adds that these could help researchers understand the environmental changes the Great Barrier Reef has gone through for over 10,000 years. The findings could also open up other studies that focus on modern marine life that reside within and around the bioherms.

The James Cook University researcher suggests employing sub-surface geophysical surveys, sediment coring and autonomous underwater vehicle technologies to gather more insight about the donut-shaped mounds. Beaman adds that further investigations will focus on their physical, chemical and biological processes.