The mystery of the sea-grass ‘fairy circles’ that have been cropping up under the surface of the sea has finally been solved.
The rings appear as glowing ovals in the Mediterranean and Baltic sea and are the result of large ‘bald patches’ devoid of vegetation in seagrass meadows.
Research has now revealed that the bare circles are caused by contamination by foreign species.
Scientists claim that the bizarre patches are a sign that entire ecosystems are at risk of extinction.
The circles have been found around the Danish coast as well as the Balearic islands, including Mallorca.
Invading species are being driven into these areas by polluted waters and climate change, the researchers, from the University of the Balearic Islands in Palma, Mallorca said.
‘The spatial organisation of vegetation landscapes is a key factor in the assessment of ecosystem health and functioning,’ lead researcher Daniel Ruiz-Reynés wrote in his paper Fairy Circle Landscapes Under The Sea, published by Science Advances.
‘Spatial configurations of vegetation landscapes act as potential indicators of climatic or human forcing affecting the ecosystem.’
The fairy circles indicate that sea-grass, known scientifically as Posidonia oceanica, in the affected regions is at risk.
A loss of sea-grass populations could dramatically alter the planet’s larger ecosystem, the researchers said.
Mr Ruiz-Reynés suggested that the circles are more prevalent than scientists realise because they are hidden under the sea.
‘Satellite images and side-scan cartography reveals that complex seascapes are abundant in meadows of Posidonia oceanica, suggesting that self-organised submarine vegetation patterns may be prevalent but have remained thus far largely hidden under the sea.’
Although the sea-grass around Mallorca ‘is a strongly clonal plant’, Mr Ruiz-Reynés said that its slow growth rate of just a few centimeters per year means that losses are ‘essentially irreversible’.
The Mallorca team used a mathematical model based on seagrass growth rates and long-distance interactions between underwater plants to uncover that competition for resources is the key driver of fairy circle formation.
The study showed that this competition radically changes the dynamics of seagrass growth, triggering the behaviour across several kilometres of the seabed.
This behaviour is difficult to predict using the simple rules of plant growth, study coauthor Dr Damià Gomila said.
‘Starting from a microscopic description of the proliferation of clonal plants (such as posidonia) and of the theory of pattern formation, a macroscopic model has been developed,’ he said.
‘This model is capable of reproducing the various structures observed on the seabed and associating the different landscapes to the conditions of mortality.’
The result is a useful tool that helps scientists to better understand competition mechanisms in underwater plantlife.
Wildlife competition mechanisms are diverse and often difficult to determine.
In marine ecosystems, access to natural resources such as light and nutrients, as well as tidal forces, are crucial factors.
These mechanisms allow for non-local interactions between plants that span several metres.
‘In other words, plants in a given region can limit the growth of distant plants, so that slightly more populated areas inhibit their environment more than their environment inhibits them,’ Dr Gomila said.
The research follows a 2014 study into the origin of similar fairy circles found in a different species of underwater plant, also off the coast of Denmark.
The strange underwater rings, which were formed of eelgrass and measured up to 49ft (15m) wide, were caused by poison.
Danish biologists confirmed that the circles had ‘nothing to do with either bomb craters or landing marks for aliens’.
Instead, they believe the rings form because of the circular pattern in which eelgrass naturally grows and the toxin killing off older, weaker plants.
Studying the mud surrounding the bizarre rings, they discovered high levels of sulfide, which is poisonous to the grass and can gradually build up on a chalky seabed.
The toxin can also occur if agricultural pollutants leak into the water, NBC News reported.
Underwater fairy circles are named after strange patches of bare earth found dotted across grassy fields in Namibia that are also dubbed fairy circles.
The ovals have long been one of nature’s greatest mysteries, prompting wild theories they were created by aliens or legendary gods.
In January, a group of scientists led by Princeton University finally unravelled what causes these these fairy circles to form in their millions.
Researchers said these self-organised regular vegetation patterns are created by a combination of plant and insect behaviour.
The team looked at two leading theories for the fairy circles to make the discovery.
The first theory suggests that plants around the fairy circles help their neighbors but compete with distant individuals in a tug-of-war for water and other scarce nutrients.
The tug of war causes the landscape to organise into rings of deep-rooted plants that are capable of draining water from a main reservoir.
The second theory argues the circles are formed by subterranean ecosystem engineers, such as termites, ants or rodents.
According to the termite theory, a species called Psammotermes allocerus is engineering the circles by destroying the plants above them.
The two theories on their own aren’t enough to explain the bare patches.
But Corina Tarnita and colleagues at Princeton University combined both of these theories into a computer simulation.
They showed that, instead of one or the other, a combination of competition between subterranean social-insect colonies of the same species and a tug of war between plants can explain the self-organised regular vegetation patterns.