Marimo: Introduction
Marimo are a rare type of green algae that form in lakes and marshes in relatively cold regions like Russia and parts of North America. In the Ainu language, Marimo are called torasanbe which means “spirit of the lake.” In Japan, Marimo were first discovered in Shurikomabetsu Bay in Lake Akan in 1897 by Sapporo Agricultural College (present-day Hokkaido University) student Kawakami Takiya (1871–1915), who was conducting research on local vegetation. Inspired by their appearance, he named the organisms “Marimo,” which means “round algae.” There are three different types of Marimo: long threads or tufts that cling to rocks and shells, tangled clumps that float in the water or accumulate at the bottom of lakes, and round balls. The environmental conditions at Lake Akan are perfect for the growth of circular Marimo, and the lake is the only place in the world where they regularly grow to diameters over 15 cm. Lake Akan’s Marimo were designated as a Special Natural Monument of Japan, recognizing the area’s ability to grow these large, beautiful, and rare spherical plants.
Marimo: Ecology
Marimo are a type of green algae that prefer cold water environments and are commonly found widely distributed in lakes and marshes in high latitudes of the Northern Hemisphere. They are shade-loving plants and can perform photosynthesis even on the bottom of lakes where there is little sunlight. Spherical Marimo are formed when many thread-like Marimo bunch together.
Marimo: Conservation Efforts
As a large and beautiful spherical species of algae seen nowhere else in the world, Lake Akan’s Marimo were designated a Natural Monument in 1921 and a Special Natural Monument in 1952. At the time of discovery, Marimo inhabited four different locations around Lake Akan. However, two colonies on the western shore became extinct during the 1940s due to sediment entering the lake from lumber transportation. The population of Marimo at the two remaining sites continued to decrease due to the large numbers of visitors who were taking them home, as well as lower water levels caused by hydroelectric power generation. In 1950, water levels at Lake Akan decreased so much that the Marimo began to wilt, resulting in a significant population reduction. Seeing this, local people came together to protect the Marimo and established the Human Association for Marimo in Lake Akan (now the Conservation Society of Marimo in Lake Akan). The Marimo Festival was created with the aim of encouraging people around Japan to return to Lake Akan the Marimo that they had collected. A traditional Ainu spiritual ritual is performed at the festival. It became one of Lake Akan’s most famous annual events and is now a popular opportunity to learn about these organisms and their conservation while also experiencing Ainu culture. There are Marimo field trips for children, and events where participants return to the lake Marimo that have been washed up on the shore.
