Editing Marimo (section)

==Ecology==
{{More citations needed section|date=May 2021}}
[[File:Lake_Akan_Kushiro_Hokkaido_Japan05n.jpg|thumb|[[Lake Akan]] and Mount Oakan in Japan.]]
The existence of marimo colonies depends on the adaptation of the species to low light conditions, combined with the dynamic interaction of wind-induced currents, light regime, lake morphology, bottom substrate, and sedimentation.

=== Size ===
[[File:Gałęzatka kulista (Cladophora aegagropila).jpg|thumb|Marimo in an aquarium]]
The growth rate of marimo is about {{convert|5|mm|in|1|abbr=on}} per year. In [[Lake Akan]] in Japan they grow particularly large, up to {{convert|20|–|30|cm|in|round=0.5|abbr=on}}. [[Mývatn|Lake Mývatn]], Iceland, had dense colonies of marimo that grow to about {{convert|12|cm|in|0|abbr=on}} in diameter and formed well defined patches on the lake floor at depths ranging from {{convert|2|–|2.5|m|ft|abbr=on}}.

=== Shape ===
The round shape of the marimo is maintained by gentle wave action that occasionally turns it. The best environment for that are shallow lakes with sandy bottoms.<ref name="population-decline"/>

The balls are green all the way round which guarantees that they can [[Photosynthesis|photosynthesize]] no matter which side is turned upwards. Inside, the ball is also green and packed with dormant [[chloroplast]]s which become active in a matter of hours if the ball breaks apart. The wave action also cleans the balls of [[detritus|dead organic material]].

As some colonies have two or even three layers of marimo balls, wave action is needed to tumble them around so each ball reaches the light. The spherical shape has a low [[surface-area-to-volume ratio]] compared to a [[leaf]], which limits [[photosynthesis]] and therefore limits the maximum size of the marimo balls.

=== Habitat ===
Marimo's preferred [[habitat]] is in lakes with a low or moderate biological activity, and with moderate or high levels of [[calcium]].<ref name="population-decline" />

=== Distribution ===
The species is mainly found in the areas of Europe previously covered in [[glacier]]s (Northern-Europe), and in several places in Japan. It has been found in North America, but it is rare, as well as in Australia.<ref name="population-decline" />

===Population decline===
The species is sensitive to the amount of nutrients in the water. An [[Eutrophication|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.<ref name="population-decline" />

The species still exists in [[Lake Zell]] 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.<ref name="population-decline" />
[[File:Mývatn-pjt.jpg|thumb|320x320px|[[Mývatn|Lake Mývatn]] in Iceland.]]
Dense colonies of marimo were discovered in [[Mývatn|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.<ref>{{Cite news|url=https://www.mbl.is/frettir/innlent/2014/05/02/einkenni_myvatns_ad_hverfa/|title=Einkenni Mývatns að hverfa|date=2014-05-02|work=[[Morgunblaðið]]|language=is}}</ref> The ecosystem is now improving and small marimo balls are forming again.<ref>{{Cite web|url=https://icelandmag.is/article/unexpected-good-news-lake-myvatn-large-quantities-marimo-wash-ashore|title=Unexpected good news from lake Mývatn: Large quantities of Marimo wash ashore|website=Icelandmag}}</ref><ref>{{Cite web|url=https://icelandmag.is/article/great-news-myvatn-lake-unique-marimo-colonies-grow-second-year-a-row|title=Great news from Mývatn lake: Unique marimo colonies grow second year in a row|website=Icelandmag}}</ref>

The species can still be found in several places in Japan, but populations have also declined there.<ref name="population-decline" /> At Lake Akan, a great effort is spent on the conservation of the lake balls.

The marimo has been a [[Conservation status|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]].