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!
Radioactivity from oil and gas wastewater persists in Pennsylvania stream sediments
22.01.2018 | Duke University
World’s oldest known oxygen oasis discovered
18.01.2018 | Eberhard Karls Universität Tübingen
On the way to an intelligent laboratory, physicists from Innsbruck and Vienna present an artificial agent that autonomously designs quantum experiments. In initial experiments, the system has independently (re)discovered experimental techniques that are nowadays standard in modern quantum optical laboratories. This shows how machines could play a more creative role in research in the future.
We carry smartphones in our pockets, the streets are dotted with semi-autonomous cars, but in the research laboratory experiments are still being designed by...
What enables electrons to be transferred swiftly, for example during photosynthesis? An interdisciplinary team of researchers has worked out the details of how...
For the first time, scientists have precisely measured the effective electrical charge of a single molecule in solution. This fundamental insight of an SNSF Professor could also pave the way for future medical diagnostics.
Electrical charge is one of the key properties that allows molecules to interact. Life itself depends on this phenomenon: many biological processes involve...
At the JEC World Composite Show in Paris in March 2018, the Fraunhofer Institute for Laser Technology ILT will be focusing on the latest trends and innovations in laser machining of composites. Among other things, researchers at the booth shared with the Aachen Center for Integrative Lightweight Production (AZL) will demonstrate how lasers can be used for joining, structuring, cutting and drilling composite materials.
No other industry has attracted as much public attention to composite materials as the automotive industry, which along with the aerospace industry is a driver...
Scientists at Tokyo Institute of Technology (Tokyo Tech) and Tohoku University have developed high-quality GFO epitaxial films and systematically investigated their ferroelectric and ferromagnetic properties. They also demonstrated the room-temperature magnetocapacitance effects of these GFO thin films.
Multiferroic materials show magnetically driven ferroelectricity. They are attracting increasing attention because of their fascinating properties such as...
08.01.2018 | Event News
11.12.2017 | Event News
08.12.2017 | Event News
22.01.2018 | Materials Sciences
22.01.2018 | Earth Sciences
22.01.2018 | Life Sciences