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 CO2 particles from a high concentration (the air) to where there is less of it (the ocean). Thus by way of water, seagrass removes CO2 from the air.
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.
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.
“We found unexpected blue carbon hotspots”
About one quarter of the emissions we emit every year end up in our oceans. Seagrass meadows near the coast play a role that has so far been underestimated: they absorb a lot of carbon dioxide, more than previously expected. Angela Stevenson from GEOMAR Helmholtz Center for Ocean Research Kiel researches seagrass meadows in the German Baltic Sea. The first results are now available.
“For seagrass meadows the impacts could be severe”
Two thirds of the earth's surface is covered by water. Oceans play an important role to us humans - they are food sources, heat stores, trade routes and one of the most important stores of carbon dioxide (CO2). In particular, seagrass meadows along the coasts absorb a lot of CO2, but this ecosystem is sensitive to the effects of climate change and could lose much of its storage function.
Climate facts: Why we need peatlands
Peatlands store large amounts of carbon and thus keep greenhouse gases out of the air – if they aren’t drained as they have been in Germany. But the draining can be reversed by rewetting the peatlands and using them differently. It’s as big a challenge as phasing out coal, experts say. But it’s worth the effort, as our new fact sheet shows.
