The mysterious undersea circles off the Baltic coast of Denmark were photographed in 2008 and since then people have tried to find an explanation. Image © University of Southern Denmark
The strange circular formations, can be up to 15 meters in diameter, appeared in 2008 in the shallow waters off the white cliffs of chalk on the island Møn in Denmark, were so many that they made it to the media.
Biologists concluded that the circles consisted of eelgrass plants growing on the bottom of the shallow water. But only now they find out why the eelgrass grows in circles.
Biologists Marianne Holmer from University of Southern Denmark and Jens Borum from University of Copenhagen, said:
“It has nothing to do with either bomb craters or landing marks for aliens. Nor with fairies, who in the old days got the blame for similar phenomena on land, the fairy rings in lawns being a well known example.
We have studied the mud that accumulates among the eelgrass plants and we can see that the mud contains a substance that is toxic to eelgrass.
Most mud gets washed away from the barren, chalky seabed, but like trees trap soil on an exposed hillside, eelgrass plants trap the mud. And therefore there will be a high concentrations of sulfide-rich mud among the eelgrass plants.
Eelgrass populations grow vegetatively by stolons which spread radially in all directions and therefore each plant creates a circular growth pattern. When the sulfide begins to work, it starts with the oldest and thus the inner part of the population because here is an increased release of toxic sulfide and uptake by plants due to accumulation of mud. The result is an exceptional circular shape, where only the rim of the circle survives – like fairy rings in a lawn.”