Strong typhoon a lifesaver for treasured algae in Hokkaido lake

[Japan] A devastating typhoon that pounded Japan’s northernmost main island this summer is being credited with saving a rare type of ball-shaped algae from extinction.

Strong winds whipped up by the seventh typhoon of the season stirred the surface of Lake Akanko here so violently that 122 tons of aquatic plants washed ashore to the north of the lake’s Churui Bay, where marimo colonies thrive.

The green algae, which are found in high-altitude regions of world, are designated as a special natural treasure by the government.

Typhoon No. 7 lashed Hokkaido on Aug. 17. Only a small fraction of the marimo, whose scientific name is Cladophora aegagropila, were washed ashore.

As hydrophytes, or aquatic plants, had prevented the rare alga from growing properly, the devastation caused by the typhoon cleaned up the lake and drastically improved the habitat for the marimo.

The lake’s water quality deteriorated with waste water discharged from a nearby hot spring resort. But it has gradually been improving since a sewage system was installed about 20 years ago, allowing plants to flourish in wider areas in the shallows.

As a result, the ball-like alga became unable to rotate or even move to photosynthesize in their colonies a few years ago. Because of that, a large number of marimo withered or collapsed rapidly.

In an effort to rescue marimo, local authorities took action.

As the marimo colonies thrive in a special protection zone in a national park, local authorities obtained permission from the Environment Ministry to remove aquatic plants in the lake on a trial basis. The effort started last year.

The typhoon made it unnecessary to remove hydrophytes for now, but they will regenerate unless the lake is subjected to very strong winds again.

“The latest typhoon showed us how much water plants should be removed to enable marimo to co-exist with them,” said Isamu Wakana, director of the Marimo Exhibition and Observation Center of Kushiro city’s education board. “The phenomenon was significant from that aspect.”


Photo: Water plants uprooted by a typhoon allowed treasured marimo ball-shaped alga to thrive in Lake Akanko in Kushiro, Hokkaido. This photo was taken on Aug. 22. (Provided by the Marimo Exhibition and Observation Center of the Kushiro city education board)

View original article at: Strong typhoon a lifesaver for treasured algae in Hokkaido lake

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