A new study from the University of Tokyo has found that climate change could cause rare underwater "marimo" algae balls to be exposed to too much sunlight, leading to their death. Marimo is green algae that form into balls, and the largest ones can be found in Lake Akan in Japan. These algae are typically protected from excessive winter sunlight by a layer of ice and snow, but global warming is causing the ice to thin.
The study found that the algae can withstand bright light for up to four hours and recover if placed under moderate light for 30 minutes. However, prolonged exposure to bright light for six hours or more resulted in the death of the algae. The researchers hope that this discovery will raise awareness about the impact of climate change on this endangered species and the need to protect their habitat.
Marimo is a type of aquatic algae that has gained popularity as a pet with tourists, nature enthusiasts, and aquarium owners. They are soft, green balls of algae that range in size from a pea to a basketball and are formed when strands of the Aegagropila linnaei algae are rolled together by the movement of water in a lake. Marimo is only found in a few countries, and the largest ones, which can grow up to 30 centimeters in diameter, can be found in Lake Akan in Japan. The study was reported in the International Journal of Molecular Sciences.
Algae Balls' Environmental Significance
In Japan, marimo has a strong cultural significance and is celebrated with an annual festival, merchandise, and even a mascot. Despite their popularity, marimo are endangered, and their numbers are decreasing globally. Marimo relies on nutrients and photosynthesis to survive, and their decline is often due to human activities that alter or pollute the freshwater lakes where they live. However, there has not been much research on the effect of changing access to sunlight on marimo. It is known that marimo can survive bright sunlight in warm summer waters, but the photosynthetic properties of marimo in low winter temperatures have not been studied.
Project Assistant Professor Masaru Kono from the Graduate School of Science at the University of Tokyo noted that there was a lack of understanding about how marimo would respond to a low-temperature, high-light-intensity environment and whether they could tolerate it. This motivated the team to conduct their study to understand better the effect of bright light on marimo in cold temperatures.
Kono and his team conducted their study by visiting Lake Akan's Churui Bay in the winter to measure the temperature and light intensity underwater, both with and without ice cover. To do this, they bored a small hole in the ice 80 meters offshore and then carved out a large 2.5-meter by 2.5-meter square to take readings from. They also collected several marimo balls, about the size of a shot put by hand.
Back in Tokyo, the team recreated the environmental conditions in the lab by using trays of ice made with an icemaker and white LED lamps. They tested the normal photosynthetic ability of the algae strands removed from the marimo balls and then placed them in containers on the ice under the artificial light, adjusting the intensity and duration of the light exposure.
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Extreme Climate Affecting 'Marimo' Balls
The team's research showed that damaged cells in marimo can repair themselves after being exposed to simulated strong daylight for up to four hours at cold temperatures (2-4 degrees Celsius) as long as they are exposed to moderate light for 30 minutes. This moderate light has a restorative effect on the algae but does not occur in the dark. However, if the algae are exposed to strong daylight for six hours or more, certain cells involved in photosynthesis are damaged, and the algae die, even when treated with moderate light. These results suggest that photoinhibition, or the inability to photosynthesize due to cell damage, would seriously threaten marimo in Lake Akan if global warming continues and the ice cover recedes.
Lake Akan receives more than 10 hours of sunlight daily in the winter. The research team plans to continue their study by examining the effect of bright light on whole marimo balls to determine if the outcome is the same as with the smaller threads. In the current study, the team used dissected filamentous cells and did not consider the protective effect of the spherical shape of marimo or how it might affect the response to bright light exposure.
However, suppose the surface cells are damaged by prolonged exposure to direct sunlight. In that case, it could potentially affect the maintenance of the round shape of the marimo and lead to the disappearance of the giant marimo. Kono noted that it would be important to constantly monitor the conditions at Lake Akan in the future better to understand the impact of bright light on marimo.
The scientists hope their research will help local and national governments understand the importance of protecting Japan's unique marimo and its habitat. He also believes it will serve as an opportunity for people to think more seriously about the effects of global warming.
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