How Forming 'Fairy Circles' May Help Salt Marshes Adapt to Climate Change

Mysterious circular patterns, often called "fairy circles" appear all around the world in different climates—from the arid regions of Australia and Namibia to the salt marshes along China's coastline. The peculiar patterns have long captivated humans, sparking myths of fairies or deities creating them. But new research published in Science Advances shows not all fairy circles behave and form the same way.

Fairy rings that form in salt marshes seem to change shape based on nutrient availability and could indicate the ecosystem's resilience to climate change, reports Bethan Ackerley for New Scientist.

Previous research has focused on fairy circles that retain a similar shape and pattern over time. Their spotty formation was attributed to Alan Turing's mathematical theory known as a Turing Pattern. These Turing rings form by chemically repelling each other, leading to distinct identical circular patterns, reports Tara Yarlagadda for Inverse. But transient fairy circles that change shape over time have not been widely studied. Unlike stable fairy circles, transient ones vary in shape, sometimes appearing as a single spot, rings, concentric circles, or eventually, merging together as one, reports New Scientist.

To find out why transient circles form in salt marshes and exhibit this behavior, Li-Xia Zhao and her team from East China Normal University used computer modeling to recreate ring patterns seen in the marshes. They then simulated nutrient depletion in the center of the rings and rising sulfide levels caused by bacteria decomposing plant matter, reports Meagan Cantwell for Science. At various points in and around the fairy circles, the researchers collected soil samples and studied two plant species, a sedge (Scirpus mariqueter) and salt marsh cordgrass (Spartina alterniflora), reports New Scientist.

Zhao and her team found that samples taken from the center of the ring had higher concentrations of sulfides and less access to nitrogen—and both conditions limit plant growth. The fairy circles' varying shapes correlated with where nutrients and oxygen were depleted, reports New Scientist. When the researchers added fertilizer to the circles' outer edge, they found little to no difference of growth, but when added to the center of the ring, they found growth where no plants previously were, Science reports.

"Through a controlled experiment with the addition of nutrients, we further found that the nutrient depletion mechanism has a dominant contribution to the self-organizing patterns of such 'fairy circles,'" study co-author Quan-Xing Liu, an environmental scientist at East China Normal University, tells Inverse.

Compared to the Turing-style fairy circles that repel each other, the merging behavior observed in these salt marshes may demonstrate resilience to environmental stressors and the ability to form a lush ecosystem again after oxygen and nutrient depletions, reports Inverse. Researchers suspect the salt marshes may be an ecosystem that could survive a climate crisis without irreversible damage.

"It sort of teaches you what the limiting factors for a vegetation are. It's learning about what determines salt marsh expansion to help then restore them, because they are very important ecosystems. They are carbon absorbers, so they are also important to counter the effect of human CO2 emissions," says co-author Johan van de Koppel of the University of Groningen, the Netherlands, to New Scientist.

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