In Hokkaido, Japan, at the bottom of Lake Akan, there are benign underwater algae balls that can grow to be larger than basketballs during the winter months. They are protected from death by a shield of ice on the surface of the water. Due to global warming, this shield is expected to thin, which could put the balls in danger of extinction, according to a study by the University of Tokyo.
These balls are called marimo algae balls, which are often mistakenly referred to as marimo moss balls in Japan. They have a soft, bright green color and are quite popular in Japan, where they have their own somewhat off-color mascot. They are often kept as pets in fish tanks and have their festival. There is even a center for observing these balls in the middle of Hokkaido’s lake Akan that attracts over half a million visitors each year.
Aegagropila linnaei is the scientific name for these balls, which form due to the rolling motion of the lake. They start out as small as a pea, grow about five millimeters per year, get up to a foot wide, and can live for centuries. Much like trees, they develop growth rings as they age. These balls are rapidly disappearing from lakes around the world due to pollution and human intervention, and only the larger specimens of these balls remain in Lake Akan.
The University of Tokyo researchers conducted a study to see how the reduction in access to sunlight during winter months might be affecting these organisms. The team measured the intensity of sunlight underwater in Lake Akan when the lake was ice-free and when it was covered in ice. They then harvested a few small marimo balls measuring about 10 to 15 cm in diameter and took them back to the lab. There they exposed strands of algae from the balls to ice and artificial light that recreated the conditions they observed at the lake.
It was discovered that in cold water, A. linnaei enters a state of hibernation, with only a thin coating of algal filaments on its surface, which is quite different from its more robust and furry „summer coat.“ Thus, it can only handle up to six hours of sunlight a day in cold water before cells associated with photosynthesis die off, leading to the entire organism’s death. Even if the balls were degraded after four hours of strong light exposure, it only took 30 minutes of moderate light to help them regenerate. Interestingly, moderate light was needed to help them restore themselves; darkness did not have the same effect.
Since Lake Akan gets more than 10 hours of sunlight per day in winter months, the ice and snow completely covering the lake shield the marimo balls from too much sunlight. As that ice thins due to warming temperatures and more sunlight makes its way through the winter water, the balls will come under a greater threat of extinction. The researchers plan to study the effect of excess light on complete balls of marimo to see if the round structure of the organism might provide additional protection from the harmful rays.
The study has been published in the International Journal of Molecular Sciences.
Source: University of Tokyo