Danish divers fight climate change by planting seagrass underwater

This project, the first of its kind in the country, brings attention to the fact that carbon-capturing greenery is not limited to dry land only

The University of Southern Denmark (SDU) leads a project that helps offset the country’s carbon footprint – and it does so from under the sea. Researchers have carried out a successful experiment which involved the physical replanting of valuable eelgrass on the seabed in two of the country’s fjords: Horsens and Vejle.

The thing is, the more than 70 species of seagrasses are among the most poorly protected, yet they make up many of the world’s coastal habitats. They can capture and store carbon better than any other plant. Seagrass sequestration of carbon is 35 times faster than the rainforest. It turns out that the best carbon sink might lie underwater hidden from sight.

Planting - better than sowing

According to scientific estimates, an acre (which is just over half the size of a football field) of seagrass can capture 335 kg of carbon per year. That’s the same amount emitted by a car travelling 6,212 kilometres.

Seagrass is also essential for wildlife that uses the underwater meadows as a habitat.

“The eelgrass, or the seagrass, is fundamental to life in Vejle Fjord and our inner seas in Denmark," explains Mads Fjeldsoe Christensen, a biologist and project manager from the Municipality of Vejle, as quoted by Euronews. "It's like a nursery for the small fishes. It's like the forests of the sea."

The problem is that since 1900, Denmark has lost 80-90% of the once lush beds of eelgrass that grew along our shores and in fjords. The reasons are complex and have to do with overfishing, runoff from farm waste and climate change. Given the importance of the plants for carbon capture and biodiversity, scientists have been trying to manually aid their restoration.

Initially, the effort was concentrated on sowing eelgrass seeds, the way you would in a field, but it turned out to be very ineffective. So, the attention turned to planting instead. But even that is a difficult task.

“If you do not prepare carefully and make sure to choose suitable locations, it will most likely go wrong. We can also see that larger areas with at least 5,000-10,000 transplants have a better chance than smaller areas,” explained Troes Lange, leader of the university research team, as quoted by SDU’s press service.

The team initiated a two-year project on a small scale which saw that seagrass density grew 70 times and the coverage expanded by 30%. Now, they are taking the next step by hiring volunteer divers to plant the individual shoots (attached to degradable iron nails).