Featured Research

from universities, journals, and other organizations

Mysterious ocean circles off the Baltic coast explained

Date:
January 30, 2014
Source:
University of Southern Denmark
Summary:
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 finally present a scientific explanation.

Eelgrass growing in the shallow water off the coast in circle shape.
Credit: Ole Pedersen

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.

Related Articles


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

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.


Story Source:

The above story is based on materials provided by University of Southern Denmark. Note: Materials may be edited for content and length.


Journal Reference:

  1. Jens Borum, Ane Løvendahl Raun, Harald Hasler-Sheetal, Mia Østergaard Pedersen, Ole Pedersen, Marianne Holmer. Eelgrass fairy rings: sulfide as inhibiting agent. Marine Biology, 2013; 161 (2): 351 DOI: 10.1007/s00227-013-2340-3

Cite This Page:

University of Southern Denmark. "Mysterious ocean circles off the Baltic coast explained." ScienceDaily. ScienceDaily, 30 January 2014. <www.sciencedaily.com/releases/2014/01/140130102040.htm>.
University of Southern Denmark. (2014, January 30). Mysterious ocean circles off the Baltic coast explained. ScienceDaily. Retrieved October 30, 2014 from www.sciencedaily.com/releases/2014/01/140130102040.htm
University of Southern Denmark. "Mysterious ocean circles off the Baltic coast explained." ScienceDaily. www.sciencedaily.com/releases/2014/01/140130102040.htm (accessed October 30, 2014).

Share This



More Plants & Animals News

Thursday, October 30, 2014

Featured Research

from universities, journals, and other organizations


Featured Videos

from AP, Reuters, AFP, and other news services

How A Chorus Led Scientists To A New Frog Species

How A Chorus Led Scientists To A New Frog Species

Newsy (Oct. 30, 2014) — A frog noticed by a conservationist on New York's Staten Island has been confirmed as a new species after extensive study and genetic testing. Video provided by Newsy
Powered by NewsLook.com
Surfer Accidentally Stands on Shark, Gets Bitten

Surfer Accidentally Stands on Shark, Gets Bitten

AP (Oct. 30, 2014) — A 20-year-old competition surfer said on Thursday he accidentally stepped on a shark's head before it bit him off the Australian east coast. (Oct. 30) Video provided by AP
Powered by NewsLook.com
Ebola Inflicts Heavy Toll on Guinean Potato Trade

Ebola Inflicts Heavy Toll on Guinean Potato Trade

AFP (Oct. 30, 2014) — The Ebola epidemic has seen Senegal and Guinea Bissau close its borders with Guinea and the economic consequences have started to be felt, especially in Fouta Djallon, where the renowned potato industry has been hit hard. Duration: 02:01 Video provided by AFP
Powered by NewsLook.com
Genetically Altered Glowing Flower on Display in Tokyo

Genetically Altered Glowing Flower on Display in Tokyo

Reuters - Innovations Video Online (Oct. 30, 2014) — Just in time for Halloween, a glowing flower goes on display in Tokyo. Instead of sorcery and magic, its creators used science to genetically modify the flower, adding a naturally fluorescent plankton protein to its genetic mix. Ben Gruber reports. Video provided by Reuters
Powered by NewsLook.com

Search ScienceDaily

Number of stories in archives: 140,361

Find with keyword(s):
 
Enter a keyword or phrase to search ScienceDaily for related topics and research stories.

Save/Print:
Share:  

Breaking News:

Strange & Offbeat Stories

 

Plants & Animals

Earth & Climate

Fossils & Ruins

In Other News

... from NewsDaily.com

Science News

Health News

Environment News

Technology News



Save/Print:
Share:  

Free Subscriptions


Get the latest science news with ScienceDaily's free email newsletters, updated daily and weekly. Or view hourly updated newsfeeds in your RSS reader:

Get Social & Mobile


Keep up to date with the latest news from ScienceDaily via social networks and mobile apps:

Have Feedback?


Tell us what you think of ScienceDaily -- we welcome both positive and negative comments. Have any problems using the site? Questions?
Mobile iPhone Android Web
Follow Facebook Twitter Google+
Subscribe RSS Feeds Email Newsletters
Latest Headlines Health & Medicine Mind & Brain Space & Time Matter & Energy Computers & Math Plants & Animals Earth & Climate Fossils & Ruins