Just like their landlubber cousins, underwater plants photosynthesize, using sunlight plus carbon dioxide to generate energy and send bubbles of oxygen fizzing toward the surface. Now, researchers have found that if you listen closely, you can hear these bubbles let out a popping sound as they detach from the algae, Hakai reports. Scientists noticed odd, high-pitched sounds coming from reefs devoid of fish life, so they set up “barren” ecosystems with only red algae in the lab. The high-pitched noises corresponded to bubbles leaving the photosynthesizing plants, they reported last month in PLOS ONE. Because too much algae can mean an ecosystem in distress, the scientists hope to use the sounds of photosynthesis to monitor undersea environments.