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Marimo (also known as Cladophora ball, moss ball, or lake ball) is a rare growth form of ''Aegagropila linnaei'' (a species of filamentous green algae) in which the algae grow into large green balls with a velvety appearance. 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 Iceland ( is, Ísland; ) is a Nordic island country in the North Atlantic Ocean and in the Arctic Ocean. Iceland is the most sparsely populated country in Europe. Iceland's capital and largest city is Reykjavík, which (along with its s ...
, but their population has been declining.


Classification and name

Marimo were first described in the 1820s by Anton E. Sauter, found in
Lake Zell Lake Zell (german: Zeller See; it, Lago di Zell) is a small freshwater lake in the Austrian Alps. It takes its name from the city of Zell am See, which is located on a small delta protruding into the lake. The lake is long and wide. It is up ...
,
Austria Austria, , bar, Östareich officially the Republic of Austria, is a country in the southern part of Central Europe, lying in the Eastern Alps. It is a federation of nine states, one of which is the capital, Vienna, the most populous ...
. The genus ''Aegagropila'' was established by Friedrich T. Kützing (1843) with ''A. linnaei'' as the type species based on its formation of spherical aggregations, but all the ''Aegagropila'' species were transferred to subgenus ''Aegagropila'' of the genus ''Cladophora'' later by the same author (Kützing 1849). Subsequently, ''A. linnaei'' was placed in the genus ''Cladophora'' in the Cladophorales and was renamed ''Cladophora aegagropila'' (L.) Rabenhorst and ''Cl. sauteri'' (Nees ex Kütz.) Kütz. Extensive DNA research in 2002 returned the name to ''Aegagropila linnaei''. The presence of chitin in the cell walls makes it distinct from the genus ''
Cladophora ''Cladophora'' is a genus of reticulated filamentous Ulvophyceae (green algae). The genus ''Cladophora'' contains many species that are very hard to tell apart and classify, mainly because of the great variation in their appearances, which is a ...
''. The algae was named ''marimo'' by the Japanese botanist Takiya Kawakami in 1898. ''Mari'' is a bouncy play ball. ''Mo'' is a generic term for plants that grow in water. The native names in Ainu are ''torasampe'' (lake goblin) and ''tokarip'' (lake roller).Irimoto, Takashi. 2004
Creation of the Marimo Festival: Ainu Identity and Ethnic Symbiosis
Senri Ethnological Studies 66:11–38.
They are sometimes sold in aquariums under the name "Japanese moss balls" although they are unrelated to moss. In Iceland the lake balls are called ''kúluskítur'' by the local fishermen at Lake Mývatn (''kúla'' = ball, ''skítur'' = muck) where the "muck" is any weeds that get entangled in their fishing nets. The generic name ''Aegagropila'' is Greek for "goat hair".


Growth forms

The algae has three growth forms: * It can grow on rocks, usually found on the shaded side of the rocks. * It can exist as free-floating filaments. Small tufts of unattached filaments frequently form a carpet on the muddy lake bottom. * It can form a lake ball where the algae grow into sizable balls of densely packed algal filaments that radiate from the center. The balls do not have a
kernel Kernel may refer to: Computing * Kernel (operating system), the central component of most operating systems * Kernel (image processing), a matrix used for image convolution * Compute kernel, in GPGPU programming * Kernel method, in machine learn ...
of any sort.


Ecology

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

The growth rate of marimo is about per year. In Lake Akan in Japan they grow particularly large, up to . Lake Mývatn, Iceland, had dense colonies of marimo that grow to about in diameter and formed well defined patches on the lake floor at depths ranging from .


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. The balls are green all the way round which guarantees that they can
photosynthesize Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored in ...
no matter which side is turned upwards. Inside, the ball is also green and packed with dormant chloroplasts which become active in a matter of hours if the ball breaks apart. The wave action also cleans the balls of 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 The surface-area-to-volume ratio, also called the surface-to-volume ratio and variously denoted sa/vol or SA:V, is the amount of surface area per unit volume of an object or collection of objects. SA:V is an important concept in science and engin ...
compared to a
leaf A leaf ( : leaves) is any of the principal appendages of a vascular plant stem, usually borne laterally aboveground and specialized for photosynthesis. Leaves are collectively called foliage, as in "autumn foliage", while the leaves, ste ...
, which limits
photosynthesis Photosynthesis is a process used by plants and other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's activities. Some of this chemical energy is stored i ...
and therefore limits the maximum size of the marimo balls.


Habitat

Marimo's preferred
habitat In ecology, the term habitat summarises the array of resources, physical and biotic factors that are present in an area, such as to support the survival and reproduction of a particular species. A species habitat can be seen as the physical ...
is in lakes with a low or moderate biological activity, and with moderate or high levels of
calcium Calcium is a chemical element with the symbol Ca and atomic number 20. As an alkaline earth metal, calcium is a reactive metal that forms a dark oxide-nitride layer when exposed to air. Its physical and chemical properties are most similar t ...
.


Distribution

The species is mainly found in the areas of Europe previously covered in
glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its ablation over many years, often centuries. It acquires distinguishing features, such as ...
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.


Population decline

The species is sensitive to the amount of nutrients in the water. An excess of nutrients (due to agriculture and
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), 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 Zell Lake Zell (german: Zeller See; it, Lago di Zell) is a small freshwater lake in the Austrian Alps. It takes its name from the city of Zell am See, which is located on a small delta protruding into the lake. The lake is long and wide. It is up ...
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 ecosystem is now improving and small marimo balls are forming again. 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 An endangered species is a species that is very likely to become extinct in the near future, either worldwide or in a particular political jurisdiction. Endangered species may be at risk due to factors such as habitat loss, poaching and invas ...
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 A nature reserve (also known as a wildlife refuge, wildlife sanctuary, biosphere reserve or bioreserve, natural or nature preserve, or nature conservation area) is a protected area of importance for flora, fauna, or features of geological or ...
.


Cultural aspects

Marimo balls are a rare curiosity. In Japan, the Ainu people hold a three-day marimo festival every October at Lake Akan. Because of their appealing appearance, the lake balls also serve as a medium for environmental education. Small balls sold as
souvenir A souvenir (), memento, keepsake, or token of remembrance is an object a person acquires for the memories the owner associates with it. A souvenir can be any object that can be collected or purchased and transported home by the traveler as a m ...
s are hand rolled from free-floating filaments. A widely marketed
stuffed toy A stuffed toy is a toy doll with an outer fabric sewn from a textile and stuffed with flexible material. They are known by many names, such as plush toys, plushies, stuffed animals, and stuffies; in Britain and Australia, they may also be ...
character known as
Marimokkori is a character popularized in Hokkaidō, Japan. Much like the Tamagotchi, the name "Marimokkori" is a portmanteau: marimo is the word for the green algae clusters that grow in some of Hokkaidō's lakes, while '' mokkori'', literally "bulge", is a ...
takes the anthropomorphic form of the marimo algae as one part of its design. Marimo are sometimes sold for display in aquariums; those often originate from Ukrainian lakes such as the Shatskyi Lakes. Balls sold in Japanese aquarium shops are of European origin; collecting them from Lake Akan is prohibited.


Contamination

On 2 March 2021, the
United States Geological Survey The United States Geological Survey (USGS), formerly simply known as the Geological Survey, is a scientific agency of the United States government. The scientists of the USGS study the landscape of the United States, its natural resources, ...
was notified that
zebra mussels The zebra mussel (''Dreissena polymorpha'') is a small freshwater mussel. The species originates from the lakes of southern Russia and Ukraine, but has been accidentally introduced to numerous other areas and has become an invasive species in ma ...
had been discovered in moss balls sold in pet stores across North America. By 8 March, invasive zebra mussels had been detected in moss balls in 21 states. These discoveries were prompted by the initial find at a
Seattle Seattle ( ) is a seaport city on the West Coast of the United States. It is the seat of King County, Washington. With a 2020 population of 737,015, it is the largest city in both the state of Washington and the Pacific Northwest regio ...
Petco Petco Health and Wellness Company, Inc. is an American pet retailer with corporate offices in San Diego and San Antonio. Petco sells pet food, products, and services, as well as certain types of live small animals. Founded in 1965 as a mail-ord ...
. Owners of fish tanks were urged to decontaminate the moss balls by boiling, freezing or bleaching them before disposing of them to prevent spread to local waterways. Petco and PetSmart voluntarily recalled moss balls in their stores. If the mussels reach open water in
Washington Washington commonly refers to: * Washington (state), United States * Washington, D.C., the capital of the United States ** A metonym for the federal government of the United States ** Washington metropolitan area, the metropolitan area centered o ...
, they could cost the state $100 million each year in maintenance for power and water systems.


See also

* List of ''Special Natural Monuments'' in Japan * '' Codium bursa'', a round marine algae


Notes


References


Bibliography

* * * * Nagasawa, S., Wakana, I. and Nagao, M. 1994. Mathematical characterization of photosynthetic and respiratory property regarding the size of Marimo's aggregation. Marimo Research 3:16–25. * Yoshida, T., Nagao, M., Wakana, I. and Yokohama, Y. 1994. Photosynthetic and respiratory property in the large size spherical aggregations of "Marimo". Marimo Research 3:1–11. * Yoshida, T., Horiguchi, T., Nagao, M., Wakana, I. and Yokohama, Y. 1998. Ultrastructural study of chloroplasts of inner layer cells of a spherical aggregation of "Marimo" (Chlorophyta) and structural changes seen in organelles after exposing to light. Marimo Research 7:1–13. * Wakana, I. 1992. A bibliography relating to "Marimo" and their habitats. Marimo Research 1:1–12.


External links


Ainu Tribe - Legend of the Marimo
{{Authority control Pithophoraceae Commemoration of Carl Linnaeus Taxa named by Friedrich Traugott Kützing