Beneath the ice: spring sunlight triggers photoinhibition and recovery in lake Akan Marimo

The marimo (Aegagropila brownii), a nationally designated Special Natural Monument of Japan, inhabits Lake Akan in Hokkaido, where environmental conditions fluctuate drastically with the seasons. Of particular concern is the period immediately after ice melt in early spring, when low water temperatures coincide with strong sunlight, posing a risk of severe damage to photosynthetic activity.

In this study, a research team led by the Astrobiology Center conducted a detailed assessment of marimo photosynthetic performance during this critical transition period, combining field observations with laboratory experiments. The results revealed that while marimo maintains healthy photosynthetic capacity in both summer and ice-covered winter conditions, their activity significantly declines just after ice melts. However, it was also found that marimo can recover this function over the following 20 to 30 days.

These findings provide valuable insight into the seasonal vulnerability of marimo and highlight the importance of spring as a critical period for conservation. The study was published in the international journal Phycological Research on September 29, 2025.