page_title: Marimo
section_title: Population decline
hierarchical_section_title: Marimo / Ecology / Population decline
caption_attribution_description: English: Aegagropila linnaei grown in a 1000ml Erlenmeyer flask
context_page_description: Marimo is a rare growth form of Aegagropila linnaei in which the algae grow into large green balls with a velvety appearance. Marimo are eukaryotic.
  The species can be found in a number of lakes and rivers in Japan and Northern Europe. Colonies of marimo balls are known to form in Japan and Iceland, but their population has been declining.
context_section_description: The species is sensitive to the amount of nutrients in the water. An excess of nutrients (due to agriculture and fish farming), along with mud deposition from human activity are thought to be the main causes for its disappearance from many lakes.
  The species still exists in Lake Zeller in Austria (where it was first discovered in the 1820s) but the lake ball growth form has not been found there since around 1910. The same has happened in most locations in England and Scotland, where mainly the attached form can be found.
  Dense colonies of marimo were discovered in Lake Mývatn in Iceland in 1978, but they have shrunk considerably since then. By 2014 the marimo had almost completely disappeared from the lake due to an excess of nutrients.
  The species can still be found in several places in Japan, but populations have also declined there. At Lake Akan, a great effort is spent on the conservation of the lake balls.
  The marimo has been a protected species in Japan since the 1920s, and in Iceland since 2006. Lake Akan is protected as a national park and Lake Mývatn is protected as a nature reserve.
caption: A. linnaei grown in a conical flask at home.
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