Marimo literally means seaweed ball. It is a species of filamentous green algae that grow into large green balls with a velvet like appearance, also known as Cladophora ball, Lake ball, and, in some cases Moss Balls.
There are three forms of Marimo; epilithic which is found growing on the shaded side of the rocks, free-floating filaments that grow as small tufts of unattached filaments sometimes forming a soft carpet on muddy lake bottoms, and a third form that takes the ball shape, where the algae grows in balls of densely packed algal filaments that radiate out from the center.
Marimo is native to Akan Lake in Japan. It was declared to be a national treasure of Japan in 1921 and people from all over the country gathered these balls in glass jars to take home as keepsakes, perhaps to bring luck, or just because they plain looked good as a centerpiece on the table at home. It is said that taking excellent care of the balls will make all your wishes come true.
Not long after a hydro-electric plant was built on the Akan river, the river was dammed and as a result water level in the lake fell dramatically, which in turn had some rather undesirable effects on the local ecosystem.
Dead and decaying Marimo began littering the shores of Lake Akan. Because of the selling of individual Marimo as souvenirs and the damming of the Akan river, the populations of Marimo balls declined rapidly. Environmentalists launched a campaign in efforts to try and protect the Marimo of Lake Akan and an appeal was made to the people of Japan to return their Marimo souvenirs. The people responded and great numbers of the Marimo were returned to their natural environment in the lake. People were so overwhelmed by the support received that they held a festival in appreciation of the selfless act. On October 7, 1950 the first of the annual Marimo Festivals was celebrated at Lake Akan.
Marimo algae balls have been observed growing in some other lakes in Japan and freshwater ponds in European countries, but only in this particular lake do they grow to be large and perfectly spherically shaped. They grow to a diameter of 25 centimeters or 10 inches at maximum.
Marimo Balls exhibit a number of interesting behaviors, including rising and sinking in a water column, responding to light, rolling around and dumping the collecting sediment from their surfaces. They can be seen rotating positions with other Marimo on different levels of the lake bottom. This phenomenon of movement allows them to be found at deeper depths than stationary plants. It also gives the appearance that Marimo Balls could even be sentient beings, and as such as much revered.
Marimo balls are just one of the latest frenzied fads to hit the aquatic plant hobby. They are good for controlling algae since they out-compete other algae species for nutrients, thus starving others and they are relatively easy to cultivate as it requires little space and no special care. It does not require fertilizing and does not need sunlight. It just needs the moss to be rinsed off and gentle tapping with your fingers to keep it in perfect spherical shape, and it survives in temperatures below 25 degrees. All types of fish are able to live with Marimo. Algae eaters will leave it alone because the plant material is tough and tangled making it difficult for them to eat. So, in a nutshell, purchase toss in, and away you go.
Domesticated marimo can grow in tap water at room temperature as long as the water is changed every one or two weeks. The water should be changed more frequently in the summer and less often in the winter months. The marimo may be refrigerated during hot weather (above 25°C), but it does not survive freezing temperatures.
A Marimo is sometimes mistaken for an animal in the aquarium because of its movement, which is another reason for the interest. Furthermore, it has a rather long life span. The largest Marimo ball is known to have lived for over 100 years. So by cultivating the algae balls under the right conditions, you could lovingly pass down a Marimo through a couple of generations, from grandparents to a grandson.
One of the main reason for Marimo gaining public favor would most likely be due to legend. There once was a daughter of a chief of an important tribe living on the banks of Lake Akan, who fell in love with a commoner. Their relationship met with the opposition of her parents. In order to be together, they ran away, metamorphosed into Marimo and lived happily ever after. Because of this myth, the Marimo has become known as the "love plant" in Japan.
Unfortunately, the population of Marimo balls continues to dwindle. Ongoing research is being carried out now to try to save or recreate this unusual form of algae. There have been no breakthroughs.
All types of fish are able to live with Marimo. Algae eaters will leave it alone because the plant material is tough and tangled making it difficult for them to eat.
Marimo tend to be slow growing in aquariums, possibly due to the conditions. Water currents in an aquarium is not as fast moving as those found in larger bodies of water.
One of the easiest ways to propagate Marimo balls is to literally take them apart, exposing all of the individual algae strings. The strings in the center of the ball are inert until they are exposed to light. These strings have the ability to rejuvenate within 4-6 hours of coming in contact with light. Marimo balls in their natural habitat will naturally break apart as they get larger.
The most difficult part of the propagation is rolling the individual strings back into a ball. Gently rolling the strings in the palm of your hand takes patience and a lot of time. A better solution is to place the new Marimo ball into a round container such as a bucket, and add a gentle circular water movement.