Making sense of the Great Barrier Reef’s mysterious green donuts
May 05, 2023

Authors: Webster, J., McNeil, M., Bostock, H.C., Nothdurft, L.D., Byrne, M.

Year: 2023

Publication: Making sense of the Great Barrier Reef’s mysterious green donuts. EOS. American Geophysical Union, Washington D.C., USA, 104.



On the outer shelf of Australia’s Great Barrier Reef (GBR), under 20–50 meters of water, lies a broad expanse of giant green “donuts.”

These seafloor circles, each several hundred meters across, aren’t the result of a rogue offshore baking experiment. Rather, they consist of the remnants of countless generations of green calcareous algae from the Halimeda genus.

The green color comes from the current generation of Halimeda living atop these bioherms, as scientists call this type of mounded deposit with a sunken center.


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