Buzz
A long-standing puzzle involving marimo, the fuzzy green algae that Japan holds dear as a national treasure, has been solved by scientists.
While marimo are typically found nestled at the bottom of rivers and lakes, their behavior is not always so stationary. They sink at night but float during the day. Until recently, researchers couldn’t explain why. According to Atlas Obscura, a recent study has unraveled the mystery: It's all about photosynthesis.
A study published in Current Biology reveals that the floating and sinking behavior of marimo is a natural result of their circadian rhythm, which is influenced by photosynthesis.
During the day, bubbles form within the spherical balls of Aegagropila linnaei algae, causing them to rise to the water's surface. To investigate what triggers the formation of these bubbles, researchers from the University of Bristol used a chemical to block photosynthesis. They found that the bubbles didn’t appear on the chemically treated marimo, and the algae balls didn’t float, even under 48 hours of continuous light exposure.
Having established that photosynthesis plays a role in marimo buoyancy, the researchers subjected their lab-grown marimo to various light conditions to determine if their circadian rhythm also affects floating behavior. The marimo were kept in 12 hours of darkness and 12 hours of light, then moved to a space with constant dim red lighting for several days. When exposed to bright light at the start of the day—mimicking natural light patterns—the marimo floated to the surface more quickly than when exposed to bright light in the middle of the day. Essentially, the marimo experienced jet lag.
The researchers propose that this day-night buoyancy cycle may help the marimo optimize their daily light intake. Since deeper water receives less light, marimo float to the surface to take full advantage of photosynthesis each day.
Marimo are now endangered in the wild, and are no longer found in many lakes that once teemed with these algae balls. According to Dora Cano-Ramirez, the study’s lead author, this decline could be due to pollution, which affects the amount of light that reaches the water, disrupting the marimo’s photosynthetic cycle.
