Bubbly Seagrass

Scientists are tuning in to seagrasses. That may tell them how much carbon the grass is storing—an important detail in understanding our changing climate.

Seagrass beds are among the most efficient carbon-storage depots on Earth. But it’s hard to know how much total carbon they’re socking away, and how the amount changes over time. Researchers have to dig up patches of grass and sediment and analyze them in the lab.

But scientists at the University of Texas at Austin are working on a new technique. Seagrasses take up carbon dioxide from the water and produce sugars with the energy of sunlight. They store the carbon in their tissues. But so much oxygen builds up that the grasses begin to blow bubbles. As the bubbles are released, they make noise. And as the seagrass soaks up more carbon dioxide, it makes more bubbles.

The researchers are developing a system that uses underwater microphones to record the sound. The sensors could cover wide areas and operate around the clock, all year long.

The scientists conducted a two-year test in Corpus Christi Bay. They listened to the natural sounds, plus artificial pulses of sound produced by the equipment. Together, that allowed the researchers to probe the oxygen in the seagrass and the water. The test showed clear changes in the soundscape as the amount of bubbles changed over daily and yearly cycles. It also told them how much seagrass was present and how healthy it was—“tuning in” to the sound of seagrass.