Forum for Science, Industry and Business

Sponsored by:     3M 
Search our Site:

 

At last: Mysterious ocean circles in the Baltic Ocean explained

31.01.2014
Are they bomb craters from World War II? Are they landing marks for aliens?

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.

... more about:
»Denmark »Pacific Ocean »Seagrass »eelgrass

"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
Seagrass is not seaweed, but a plant with flowers, leaves and roots just like plants on land. Seagrass also produces seeds that can be sown in the seabed and grow to new plants. There are approx. 60 seagrass species in the world with eelgrass (Zostera marina) in temperate areas and Halophila ovalis in tropical and subtropical areas as common species. Seagrass needs light and only grows where at least 10% of the sun's light can reach the plants.

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
jborum@bio.ku.dk
Contact Marianne Holmer
holmer@biology.sdu.dk

Birgitte Svennevig | EurekAlert!
Further information:
http://www.sdu.dk

Further reports about: Denmark Pacific Ocean Seagrass eelgrass

More articles from Earth Sciences:

nachricht Volcanic eruption masked acceleration in sea level rise
26.08.2016 | National Science Foundation

nachricht Biomass turnover time in ecosystems is halved by land use
23.08.2016 | Alpen-Adria-Universität Klagenfurt

All articles from Earth Sciences >>>

The most recent press releases about innovation >>>

Die letzten 5 Focus-News des innovations-reports im Überblick:

Im Focus: Streamlining accelerated computing for industry

PyFR code combines high accuracy with flexibility to resolve unsteady turbulence problems

Scientists and engineers striving to create the next machine-age marvel--whether it be a more aerodynamic rocket, a faster race car, or a higher-efficiency jet...

Im Focus: X-ray optics on a chip

Waveguides are widely used for filtering, confining, guiding, coupling or splitting beams of visible light. However, creating waveguides that could do the same for X-rays has posed tremendous challenges in fabrication, so they are still only in an early stage of development.

In the latest issue of Acta Crystallographica Section A: Foundations and Advances , Sarah Hoffmann-Urlaub and Tim Salditt report the fabrication and testing of...

Im Focus: Piggyback battery for microchips: TU Graz researchers develop new battery concept

Electrochemists at TU Graz have managed to use monocrystalline semiconductor silicon as an active storage electrode in lithium batteries. This enables an integrated power supply to be made for microchips with a rechargeable battery.

Small electrical gadgets, such as mobile phones, tablets or notebooks, are indispensable accompaniments of everyday life. Integrated circuits in the interiors...

Im Focus: UCI physicists confirm possible discovery of fifth force of nature

Light particle could be key to understanding dark matter in universe

Recent findings indicating the possible discovery of a previously unknown subatomic particle may be evidence of a fifth fundamental force of nature, according...

Im Focus: Wi-fi from lasers

White light from lasers demonstrates data speeds of up to 2 GB/s

A nanocrystalline material that rapidly makes white light out of blue light has been developed by KAUST researchers.

All Focus news of the innovation-report >>>

Anzeige

Anzeige

Event News

The energy transition is not possible without Geotechnics

25.08.2016 | Event News

New Ideas for the Shipping Industry

24.08.2016 | Event News

A week of excellence: 22 of the world’s best computer scientists and mathematicians in Heidelberg

12.08.2016 | Event News

 
Latest News

Symmetry crucial for building key biomaterial collagen in the lab

26.08.2016 | Health and Medicine

Volcanic eruption masked acceleration in sea level rise

26.08.2016 | Earth Sciences

Moth takes advantage of defensive compounds in Physalis fruits

26.08.2016 | Life Sciences

VideoLinks
B2B-VideoLinks
More VideoLinks >>>