Scientists Propose New Theory Of How Marimo is Formed Skip to content

Scientists Propose New Theory Of How Marimo is Formed

Scientists researching the ecosystem of Lake Mývatn in North Iceland may have finally answered the longstanding question of how Icelandic marimo, or lake balls—are formed, RÚV reports.

Marimo are perfectly round spheres measuring 10 – 15 cm across and are, as National Geographic explains, composed of an algae species that is actually quite widespread in the Northern hemisphere: Aegagropila linnaei. But the spherical form of this algae is extremely rare and only found in a few places: Lake Akan in Japan, Lake Svityaz in Ukraine, and Lake Mývatn in Iceland.

Although Mývatn’s marimo were designated a protected species in Iceland in 2006, they almost entirely disappeared from the lake in 2013. It’s thought that an excess of cyanobacteria in the lake contributed to the marimo’s decline: photosynthetic cyanobacteria obscure the surface of the water and prevent sunlight from reaching the lakebed where marimo are formed. According to Árni Einarsson, the director of the Nature Research Institute at Mývatn (Ramý), cyanobacteria are a natural part of the Mývatn ecosystem, but pollution in the lake caused an unnatural increase that then had a trickle-down effect on species like marimo.

Despite their decline, however, a small number of Mývatn’s marimo have endured. For reasons that scientists cannot entirely explain, there is less cyanobacteria in the lake this summer and the water is unusually clear—clearer, in fact, than it has been since the 80s. As such, researchers have spent the season investigating, among other things, the necessary conditions for marimo formation. This has been something of a mystery up until now.

Árni says that the scientists now think that marimo can only form in shallow and rather turbulent water. They think they begin to grow on rocks and crags on the shallow bottom of the lake, like moss. Then, as they get larger, they are ripped from their perches by waves and agitation and sent rolling freely through the water. It’s still unknown if this explanation can be applied to the large marimo that once proliferated on the Mývatn lakebed, but it is currently the scientists’ best hypothesis.

Efforts have been made to reduce the amount of cyanobacteria in the lake and hopefully, this will mean that less of it will obscure the surface of the lake in the future.

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