How does seagrass help tackle climate change?

Seagrasses are marine plants that live in coastal waters of all continents, except Antarctica. They form large underwater meadows which cover shallow parts of the ocean floor. These dense, green ecosystems take up carbon dioxide (CO2), and keep it buried below ground. This happens through a combination of processes:

  • Seagrass removes CO2 via photosynthesis.
  • It collects organic carbon from other species (e.g. algae and animals)
  • Seagrass locks up this organic carbon in the sediments.

If seagrass meadows would be restored or newly planted, they could help tackle climate change. This is a nature-based solution to revert CO2 emissions, a so-called ‘negative emission technology‘.

Seagrass removes CO2

Like land plants, seagrass needs light and CO2 to grow and stay healthy. The plants live at depths where the sun still shines through, so they can photosynthesize. Via this basic biological process, seagrass builds its organic carbon body, which means it grows. At the same time, it removes CO2 from the water. The CO2 in the water originates from the atmosphere, mixed and absorbed into the ocean through molecular diffusion at the surface. Put simply, this is the movement of COparticles from a high concentration (the air) to where there is less of it (the ocean). Thus by way of water, seagrass removes COfrom the air.

Two divers in the Baltic
Video: Seagrass meadows (German with English subtitles)

Seagrass collects carbon

Seagrass meadows also collect other species’ carbon. With their dense canopy of leaves, the plants capture floating particles, trapping them in their meadow. Some of these particles include phytoplankton, tiny plants that photosynthesize as well. In addition, seagrass meadows are inhabited by animals that seek food and shelter. When they die, their remains are buried beneath the sediments. Both trapped particles and dead remains of the animals living in these ecosystems contain carbon that is stored in the soil. This is due to the seagrass’ unique ability to prevent the decomposition of organic carbon back into CO2.

Seagrass locks up carbon

The seagrass has a thick canopy of leaves which reduces the flow of water along the ocean floor. Underground, its roots and rhizomes (subterranean stems of the plants) protect the soil from being stirred up. This way, the soil is held together and put in a state of anoxia, of oxygen deficiency where microbes cannot decompose the organic carbon, which would otherwise produce CO2 in the process. Seagrass meadows thus lock up the CO2 and prevent it from reaching the atmosphere. As long as they are sitting on top of this carbon pool they act as a protective layer for centuries and in some cases, millennia.

Vorschaubild Video "Negative Emissionen"
Video: Negative emissions (German with subtitles)

Seagrass is very efficient

Through carbon removal, collection and storage, seagrass helps tackle climate change. Seagrass meadows store carbon in a remarkably efficient way. They accumulate carbon 30 to 50 faster in their soils than the forests on land. As an example, seagrass meadows in the German Baltic Sea occupy an area of 285 square kilometers, and so have accumulated and are preventing 8.14 million tons of future CO2 emissions.

Share article