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Halo Rings Around the Reefs: Who’s Making Them?

These halo rings were first described in the 1960s and is now known as “grazing halos.” Now it has been investigated by Joshua and Elizabeth Madin, both ecologists and are husband and wife.The grazing halo theory says that the sea urchins and the fishes eat everything around the area. This leaves behind bare sand. But why “grazing halos”?

… these grazers are loathe to venture into the open, where they could be easily picked off by sharks, barracuda, snappers, and jacks. Their fear keeps them close to the reef, and their hunger keeps that zone free of greenery. Hence: grazing halos. 
At least, that was the theory. No one had ever truly tested it, so the Madins decided to do so. As they waited for the weather to calm down, they waded through the waist-deep lagoon and sowed clumps of seaweed in various locations. Anything they placed within nine meters of a patch reef was quickly eaten; everything else was largely untouched. The grazer hypothesis was right. “We thought it would be a quick open-and-closed study,” says Madin, who is now at the Hawaii Institute of Marine Biology. “But I fell down a rabbit hole. These halos are far more complex than we originally thought.”

Who could have made such things? The answer is not that simple.

Find out more on The Atlantic.

(Image Credit: CNES/ Airbus; Digital Globe)

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