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Phytoplankton, tiny plant-like organisms in the ocean, are incredibly important for life on Earth. They're a major food source for many sea creatures and produce almost half the oxygen we breathe. They also help control the climate by soaking up a lot of carbon dioxide, a gas that contributes to global warming.

Scientists want to learn more about how these phytoplankton use sunlight to make energy and oxygen, which can be useful in the context of environmental monitoring during global climate change. However, it's tricky to study this because the usual methods only give an overall average for a large group of phytoplankton, hiding the differences between individual cells, or they only give limited measurements of individual phytoplankton.

Now, researchers at The Hebrew University of Jerusalem in Israel have come up with a new way to study these organisms. They've built a system that can measure the light given off by individual phytoplankton cells, which tells them how efficiently each individual is using light.

This new technique will help scientists better understand how different types of phytoplankton react to changes in their environment. The work was presented at the , held February 15–19, 2025 in Los Angeles.

"I look at how individual plankton react to changing conditions by looking at the light that they dispose of—or in scientific terms, I look at fluorescence lifetimes. Basically, it's how the phytoplankton convert light to energy they can use later," said Paul Harris, who led the study.

This new system uses a special microscope to get a close look at individual phytoplankton cells which are sent down tiny channels. It measures the different colors of light the cells give off, which tells scientists a lot about how they're using light to make energy.

So far, Harris and colleagues have used the system to study three different types of phytoplankton, looking at how they change throughout the day and how they react to brighter light. What they found is that each type of phytoplankton has its own unique way of adjusting to changes in light, kind of like how some people put on sunglasses when it's sunny, while others might opt for a hat. Each species has its own way of dealing with light, and uses different strategies for surviving sudden changes in their conditions.

"We need to understand how these phytoplankton respond in order to predict and observe what's happening in the oceans, especially with regard to climate change as oceans warm," said Harris. "We hope to give some insight into how species are going to change," he said.

The system could also help in predicting harmful algal blooms, which can spell disaster for fish and other species in the ecosystem and even poison humans if consumed. "We could use this tool to give advanced warning of algal blooms," he pointed out.

The ability to differentiate species and determine how they are using light and energy offers a powerful tool for assessing the health and productivity of phytoplankton populations, which are essential for marine food webs and global carbon cycling.