Reduced lake ice cover due to climate change may lead to further declines in endangered species – Zoo House News

Reduced lake ice cover due to climate change may lead to further declines in endangered species – Zoo House News

  • Science
  • January 1, 2023
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Climate change could overexpose rare underwater “marimo” balls of algae to sunlight and kill them, according to a new study from the University of Tokyo. Marimo are living fluffy balls of green algae. The largest marimo in the world is located in Lake Akan on Hokkaido, the northern main island of Japan. Here they are protected from too much winter sun by a thick layer of ice and snow, but the ice is thinning due to global warming. The researchers found that the algae could survive up to four hours of bright light and would recover if then exposed to moderate light for 30 minutes. However, the algae died when exposed to bright light for six hours or more. The team hopes this discovery will highlight the threat of climate change to this endangered species and the urgent need to protect its habitat.

Some people have pet cats, others have pet rocks, but how about pet seaweed? Marimo are fluffy, squishy green balls of underwater algae that have become popular with tourists, nature lovers, and aquarium owners. Ranging in size from about a pea to a basketball, they form naturally when floating strands of the alga Aegagropila linnaei are bunched together by the gentle rolling motion of lake water. They are found in only a few countries and the largest marimo found in Lake Akan can reach up to 30 centimeters in diameter. In Japan they are so popular that they have their own annual festival, merchandise and even a mascot. However, marimo are an endangered species and their numbers are generally declining worldwide.

Marimo rely on nutrients and photosynthesis to survive. Their decline is usually attributed to human intervention altering or polluting the freshwater lakes in which they live. However, not much research has been done on the effects of changing access to sunlight. “We know that marimo can survive bright sunlight in warm summer waters, but the photosynthetic properties of marimo at low winter temperatures have not been studied, so we were intrigued by this point,” said Project Assistant Professor Masaru Kono of the Graduate School of Science at the University of Tokyo. “We wanted to find out if Marimo tolerate that and how they react to an environment with low temperature and high light intensity.”

Kono and his team visited Lake Akan’s Churui Bay in winter to measure the temperature and light intensity underwater both with and without ice cover. First, they drilled a small hole in the ice 80 meters offshore and then carved a large 2.5 by 2.5 meter square to take measurements from. They also carefully collected by hand several marimo balls the size of a shot put (10-15 cm). Back in Tokyo, the team recreated the environmental conditions using ice trays made with an ice maker and white LED lights. Strands of algae were removed from the marimo balls and tested for their normal photosynthetic ability. They were then placed in containers in the ice under artificial lights set to glow at different intensities for different periods of time.

“We have demonstrated a new finding that damaged cells in Marimo can repair themselves after exposure to simulated strong daylight in cold temperatures (2-4 degrees Celsius) for up to four hours, followed by moderate light exposure for just 30 minutes . The moderate light had a relaxing effect that wasn’t evident in the dark. However, when exposed to strong daylight for six hours or more, certain cells involved in photosynthesis were damaged and the algae died, even when exposed to moderate light,” Kono explains. “These results suggest that photoinhibition (the inability to photosynthesize due to cell damage) would pose a serious threat to Marimo in Lake Akan, which receives more than 10 hours of sunlight per day in winter as global warming progresses and ice sheet recedes.”

Next, the team wants to find out what would happen with whole marimo balls and if the result would be the same as with the smaller threads. “In the present study, we used dissected filament cells, so we did not consider the implications of the structure of the spherical marimo and how it might protect against exposure to bright light. However, if the damage to the surface cells increases with prolonged exposure to direct sunlight, in extreme cases, it can affect the maintenance of their round bodies and lead to the disappearance of the giant marimo. Therefore, we need to constantly monitor the conditions at Lake Akan going forward,” Kono said.

Kono hopes this research will help both local and national governments understand the urgent need to protect Japan’s unique marimo and their habitat. “We also hope this is an opportunity for all people to think seriously about the impact of global warming,” he said.

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Materials provided by the University of Tokyo. Note: Content can be edited for style and length.

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