Science has been fascinated by the mystery of “fairy circles” found in the dry plains of Namibia and Australia for decades now. While the debate about the cause of these strange halos continues, a team of researchers has now turned their attention to the lesser-known “submarine fairy circles” found in the waters around certain parts of Europe.

Satellite images show strange circles within the Posidonia oceanica and Zostera marina seagrass meadows of the Mediterranean Sea off the coast of Spain and the Baltic Sea near Denmark, respectively. In a study published in the journal Science Advances, scientists have used a form of sonar cartography to reveal that vast patterns of circular vegetation, known as “leopard spots”, can be found dotted over many kilometers of sea. The study notes that these halo patterns could be found throughout many of the world’s coastal waters but are “largely hidden under the sea”.

They are essentially jbare circular patches of seabed surrounded by seagrass. As you can see, they really are oddly circular. You can even scope out a few of them on Google Maps, like you can see in this satellite image near the Spanish island of Majorca.

This kind of phenomenon has been noted before on a land, as mentioned in the case of the Namibian and Australian fairy circles. The terrestrial fairy circles are always found in extremely dry lands where resources are few and far between. As such, they are believed to be caused by competition for water leading to a complex form of self-organization that creates a circular shape. Termites are also believed to contribute as one study found over 80 percent of the circles had them living within them. However, the extent of the effect of plant competition versus termite still continues to divide some scientists.

In the sea, it also seems to be an issue of competition. The seagrasses are fighting for resources, namely carbon dioxide. They usually occur throughout the shallow areas of coastal water as this is where marine life is subject to the most fierce competition. Equally, the coastal resources are easily affected by problems such as pollution, human activity, reduced water quality, and climatic changes.

The researchers believe that a deeper understanding of these submarine fairy rings could, therefore, be used as a perceivable indicator of the ocean's health.

“Because seagrass ecosystems rank among the most threatened ecosystems globally, the capacity to diagnose the proximity of seagrass meadows to tipping points for catastrophic loss based on landscape configurations provides a tool to guide conservation measures aimed at preventing further losses," the authors write.