KUSHIRO, Hokkaido – Akan marimo, a greenish algae sphere in Lake Akan that local legend claimed would take 800 years to grow to the size of a basketball, apparently grows a lot faster than was traditionally thought.
According to a study conducted by a group of marimo researchers at the education board in the town of Akan, Hokkaido, the algae balls in Lake Akan — famed for its world-class marimos — have grown to a diameter of 10 cm in just five years.
Marimos are a type of algae formed by many small strings of algae tangled together in a spherical pattern forming a velvety green surface.
Isamu Wakana, 45, leader of the Akan marimo research team, says the marimo growth pattern was found through five years of observation he and his teammates have conducted on the northern shore of Akan. The study was conducted in waters 1 meter to 1.5 meters deep in an area 100 meters from the shore.
Known by the scientific name aegagropila, marimos are found in 17 Japanese lakes, as well as elsewhere in the world. It is on the Environment Ministry’s Red Data Book, which lists endangered species.
Wakana says a typical marimo in Lake Akan grows to about 10 cm in diameter in five years, and when it reaches 30 cm, it suffers from poor photosynthesis and begins to lose its trademark spherical shape.
The common belief surrounding marimos so far is that they take several hundred years to grow. A sightseeing guidebook on Lake Akan says it takes 600 to 800 years for a marimo to grow into a 30-cm sphere.
The late Shingo Nakazawa, a professor emeritus at Yamagata University, said in his book, “Why Is Marimo Spherical?” that it takes 450-500 years for a marimo to grow to a 20-cm sphere.
According to Wakana, Nakazawa had also doubted the veracity of the glacial pace of marimo growth, telling him once that he learned of the growth rate of marimos from an Akan town brochure.
“The mystic nature of marimos made it convincing for many people to believe that they take several hundred years to grow. Understanding more about marimos, I think, would help preserve them and increase their number,” Wakana said.