Since the first images of the mysterious ocean circles off the Baltic coast of Denmark were taken in 2008, people have tried to find an explanation. Now researchers from the University of Southern Denmark and University of Copenhagen finally present a scientific explanation.
The circles in the shallow water off the coast (photo: Jacob T. Johansen, journalist)
Eelgrass growing in the shallow water off the coast in circle shape (foto: Ole Pedersen)
The first pictures appeared in 2008, taken by a tourist and showing some strange circular formations in the shallow waters off the famous white cliffs of chalk on the island Møn in Denmark. In 2011, the circles came back, and this time there were so many that they made it to the media.
Investigating biologists then concluded that the circles consisted of eelgrass plants growing on the bottom of the shallow water. But only now scientists can explain why the eelgrass grows in circles here – eelgrass usually grows as continuous meadows on the seabed.
"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", say biologists Marianne Holmer from University of Southern Denmark and Jens Borum from University of Copenhagen.
The circles of eelgrass can be up to 15 meters in diameter and their rim consists of lush green eelgrass plants. Inside the circle there can be seen only very weak or no eelgrass plants.
"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", explain Holmer and Borum.
The poison is sulfide, a substance that accumulates in the seabed off the island of Møn, because it is very calcareous and iron-deficient.
"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," explain the researchers.
Sulfide is toxic enough to weaken the old and new eelgrass plants but not toxic enough to harm adult and strong plants. And since eelgrass spreads radially from the inside out the oldest and weakest plants are located in the center of the growth circle.
Jens Borum and Marianne Holmer say:
"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".
The waters off Møn’s chalk cliffs are not the only place where sulfide destroys eelgrass. Sulfide poisoning of eelgrass is a major problem worldwide. Sulfide is often created where oxygen disappears from the seabed. This can happen when the seabed is fed nutrients from agriculture.
Underwater meadows of eelgrass and other seagrasses grow in many parts of the world where they serve as home to a variety of small animals, filter the water and trap carbon and nutrients. But the meadows are threatened in almost all regions of the world, and in several places, including Denmark, researchers and authorities work to prevent seagrasses from disappearing.Facts about seagrass
The University of Southern Denmark is a partner and coordinator of NOVA GRASS, an international five-year research project focused on the restoration of eelgrass meadows.
Ref: Eelgrass fairy rings: sulfide as inhibiting agent . Borum , Holmer , et al. Mar. Biol. Published online 12 October 2013.Contact Jens Borum
Birgitte Svennevig | EurekAlert!
New Technique for Finding Weakness in Earth’s Crust
30.09.2016 | University of Adelaide
Researcher creates a controlled rogue wave in realistic oceanic conditions
30.09.2016 | Aalto University
Heavy construction machinery is the focus of Oak Ridge National Laboratory’s latest advance in additive manufacturing research. With industry partners and university students, ORNL researchers are designing and producing the world’s first 3D printed excavator, a prototype that will leverage large-scale AM technologies and explore the feasibility of printing with metal alloys.
Increasing the size and speed of metal-based 3D printing techniques, using low-cost alloys like steel and aluminum, could create new industrial applications...
Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of light metals.
Scientists at the University of Stuttgart have now developed two new process variants that will considerably expand the areas of application for friction stir welding.
Technologie-Lizenz-Büro (TLB) GmbH supports the University of Stuttgart in patenting and marketing its innovations.
Friction stir welding is a still-young and thus often unfamiliar pressure welding process for joining flat components and semi-finished components made of...
Optical quantum computers can revolutionize computer technology. A team of researchers led by scientists from Münster University and KIT now succeeded in putting a quantum optical experimental set-up onto a chip. In doing so, they have met one of the requirements for making it possible to use photonic circuits for optical quantum computers.
Optical quantum computers are what people are pinning their hopes on for tomorrow’s computer technology – whether for tap-proof data encryption, ultrafast...
The Fraunhofer Institute for Organic Electronics, Electron Beam and Plasma Technology FEP has been developing various applications for OLED microdisplays based on organic semiconductors. By integrating the capabilities of an image sensor directly into the microdisplay, eye movements can be recorded by the smart glasses and utilized for guidance and control functions, as one example. The new design will be debuted at Augmented World Expo Europe (AWE) in Berlin at Booth B25, October 18th – 19th.
“Augmented-reality” and “wearables” have become terms we encounter almost daily. Both can make daily life a little simpler and provide valuable assistance for...
With the help of artificial intelligence, chemists from the University of Basel in Switzerland have computed the characteristics of about two million crystals made up of four chemical elements. The researchers were able to identify 90 previously unknown thermodynamically stable crystals that can be regarded as new materials. They report on their findings in the scientific journal Physical Review Letters.
Elpasolite is a glassy, transparent, shiny and soft mineral with a cubic crystal structure. First discovered in El Paso County (Colorado, USA), it can also be...
30.09.2016 | Event News
29.09.2016 | Event News
28.09.2016 | Event News
30.09.2016 | Materials Sciences
30.09.2016 | Earth Sciences
30.09.2016 | Life Sciences