It seems as though the infamous Great Barrier Reef has been masking a smaller (while still large!) donut reef behind its enormous shadow.  This discovery, after decades of research, was made in the deeper waters behind the already established Great Barrier Reef system. From the air, the limestone structures look very much like 2,300 square mile submerged donuts, hence the name donut reef.  While it is mysterious that it is just being noticed or discovered now since it is quite large in its own right and an estimated 10,000 years old; it also is a very unique shape.

The discovery, made off the northern coast of Australia, has many scientists excited. The shape has lead author Mardi McNeil from the University of Queensland quite perplexed. McNeil says, “When the three-dimensional shape of them was revealed, it was very surprising. They form these fields of donut shaped structures; sometimes they’re like singular circular rings, sometimes in groups of three or four.”  She refers to “they” or an algae species called Halimeda which is the color green when living. However, when it dies it becomes white in color and become brittle and flaky. These flakes are what can build up, over time, and create these donut like shapes that can be up to 30 feet tall and 600 feet wide.


Mystery Reef Composition

As Halimeda dies and flakes accumulate over time, they form massive mound structures called Halimeda bioherms. These Halimeda bioherms as I mentioned early can be very, very large. In fact, they stretch farther along the northern Australian coast line than anyone every predicted.

Today, the new reef is about 60 feet to 150 feet deep below the ocean’s surface so not many people have seen it in person yet.  Of the few that have dived the reef, it seems as though there are some mixed reviews. Some divers have come back and said it was lush with life and very green, while other have come back saying it is simply white limestone, like a white desert.


So how did we miss this?

Scientists have been studying the Great Barrier Reef since its accidental discovery in 1770 by Englishman Captain James Cook, who accidently ran his ship aground on it. Scientists have been primarily focused on the shallow coast beyond the Great Barrier Reef, or as they call it the inter-reef area, suspected the existent of these large mounds of dead algae. However, they suspected this ecosystem covered an area of about 800 square miles which was incorrect. Using imaging technology they have been able to find that this area is actually three times greater than they previously thought.  The study’s team used laser imaging gathered by the Australian navy, by plane, to make a 3-D map of the ocean floor.  While this technology is nothing new for mapping coral reef ecosystems, the information gathered is still incredibly eye opening.


Robin Beaman, one of the study’s authors from James Cook Univeristy comments of the findings and how we can use them to learn more about the ocean enviornment, “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. Just like tree rings- the rings can tell you the age of when it was formed and the environment it was formed in. So you’ve got 20 meter thick piles of sediment that can tell you an awful lot about the pat oceanographic history.”


The significance of this discovery

This new discovery is a great example of how little we really know about the ocean. Of all the discoveries and advancements in technology we have made thus far, an estimated mere 5% of the ocean has been explored. This new discovery could give great insight for scientists trying to better understand climate history along the Great Barrier Reef.  This is because as algae completes its life cycle and eventually calcifies, it forms layers of fossilized information. In this case that’s an estimated 10,000 years of ocean environment conditions information.

To read more about the published study, click here. 



References and photos courtesy of