Deep Water Seagrass Meadows Are Untapped Carbon Sinks

(Credit: Rich Carey/Shutterstock) Seagrass meadows cover an area roughly the size of Switzerland in the deep waters of the Great Barrier Reef lagoon. Now, a new study shows the coastal ecosystems store significant amounts of carbon. The finding suggests deep water seagrass meadows could help mitigate climate change. “If we are to help regain control of our planet’s thermostat and limit global warming, we must capitalize on the powerful ability of natural ecosystems to sequester and store carbon,” Peter Macreadie, a marine scientist at Deakin University in Victoria, Australia, who led the new research, said. “Seagrasses are brilliant in this regard because they lock up carbon in a water grave, thereby retiring carbon from the atmosphere,” he added.

Seagrasses are flowering plants that grow in salt water, often along sloping coastlines. They have roots and stems, and as their name suggests, they look a bit like grass. Seagrasses can form dense meadows. Some seagrass meadows are so large they are visible from space. Macreadie and colleagues knew seagrass meadows that grow in shallow water are able to capture and hold onto a lot of carbon. These shallow water seagrass meadows are significant “blue carbon sinks”, places where the world’s oceans and coastal ecosystems hold onto carbon, which could help to offset climate change. Macreadie and his team wondered if deep water seagrass meadows would sequester carbon as well as the shallow water meadows. So the researchers measured the amount of carbon in shallow, medium and deep water seagrass meadows at Lizard Island in the Great Barrier Reef lagoon. In a surprise find, the team discovered shallow and deep water meadows stored similar amounts of carbon, even though the deep seagrass meadows are shorter and sparser than the shallow ones. "The deep water seagrass meadows were packing as much punch as their shallow water counterparts," Macreadie said.

Then the scientists scaled up their measurements. Previous research from another group recently revealed the Great Barrier Reef lagoon’s deep water seagrass meadows encompass an area roughly the size of Switzerland. When Macreadie and colleagues’ matched their carbon estimates to include all of the deepwater grass meadows in the region, they found the area has the capacity to store 30 million tons of carbon, the researchers report in the journal Royal Society Biology Letters. “We went into this thinking that the seagrass would be locking up some carbon, but not this much,” Macreadie said. The team's findings indicate deep water seagrass meadows are major blue carbon sinks and many more may exist around the globe.