Marimo (also known as Cladophora ball, moss ball, moss ball pet, or lake ball) is a rare growth form of Aegagropila brownii (a species of filamentous green algae) in which the algae grow into large green spheres 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, but their population has been declining.
Classification and name
Marimo were first described in the 1820s by Anton E. Sauter, found in Lake Zell, Austria. 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.
The algae was named marimo by the Japanese botanist Takiya Kawakami in 1898. is a type of bouncy play ball; is a generic Japanese term for plants that grow in water. The native names in Ainu are ('lake goblin') and ('lake roller'). 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 by the local fishermen at Lake Mývatn ( meaning 'ball', meaning '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
thumb|Three common growth forms of Aegagropila linnaei: as a ball, free-floating filaments, and growth on rocks.
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 of any sort.
left|thumb|380px|A cross section of a marimo colony in Lake Mývatn.
Ecology
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
thumb|Marimo in an aquarium
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 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.
Because of their appealing appearance, the lake balls also serve as a medium for environmental education. Small balls sold as souvenirs are hand rolled from free-floating filaments. A widely marketed stuffed toy character known as Marimokkori takes the anthropomorphic form of the marimo algae as one part of its design.
Marimo are sometimes sold for display in aquariums, typically cultivated in Ukrainian lakes such as the Shatskyi Lakes. 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 Petco. Petco and PetSmart voluntarily recalled moss balls in their stores. If the mussels reach open water in Washington, they could cost the state $100 million each year in maintenance for power and water systems.