- More carbon sequestration in marine meadows and forests?
- > Tidal marshes, seagrass meadows, mangrove and kelp forests cover far less than one per cent of the ocean and coastal area, but contribute significantly to natural carbon sequestration in the seabed. Plans to expand these coastal habitats in order to increase their natural carbon dioxide uptake will probably only be successful in particular oceanic regions. Nevertheless, they may well be worthwhile for multiple reasons.
Blue carbon – an approach yielding dual benefits
Coastal ecosystems – marine carbon sinks providing indispensable additional services
Vegetation-rich coastal ecosystems such as tidal marshes, seagrass meadows, mangrove forests and kelp forests are key players in the marine carbon cycle. Taken together, plant communities are responsible for at least 30 per cent of the organic carbon stored in the seabed.
Carbon storage by these ecosystem types follows a fixed pattern: plants take up carbon dioxide and convert the carbon it contains into biomass. This is then stored in the root system (except in the case of kelp) or accumulates over time on the seabed in the form of dead branches, leaves and stalks. Sinking sediment subsequently buries the dead plant matter and much other organic material, cutting it off from oxygen. Under these conditions, the animal and plant remains cannot decompose. Instead, they form carbon reservoirs in the seabed that are in fact larger than the soil carbon stores of terrestrial forests and will remain as long as the salt marshes, seagrass meadows and mangrove forests thrive – which, ideally, can be for periods of many thousands of years.
This climate-relevant characteristic of marine meadows and forests allows for two conclusions to be drawn. Firstly, agencies and communities which protect existing marine meadows and forests effectively prevent the degradation of their carbon stocks and thus the release of large quantities of greenhouse gases. Secondly, by planting new vegetation-rich ecosytems or restoring damaged coastal ecosystems, there are hopes of enhancing their natural carbon uptake in such a way that unavoidable anthropogenic greenhouse gas emissions can be offset.
The size of the carbon dioxide removal potential of coastal ecosystems is a matter of some debate in the scientific community, as key basic knowledge is still lacking, such as the level of carbon storage in the individual coastal ecosystems. There is much evidence to suggest that there are major differences in carbon storage between locations, primarily due to local site conditions. New plantings which are designed to achieve additional carbon dioxide removal therefore only make sense in those regions where optimal growth and storage conditions prevail.
However, it would be wrong to make decisions on the restoration or possible expansion of vegetation-rich coastal ecosystems solely on the basis of their carbon removal potential. Tidal marshes, seagrass meadows, mangrove forests and kelp forests offer a long list of existential co-benefits. For instance, they produce oxygen, purify water, provide habitat and food for animals and plants, slow down waves and currents, protect the coasts from erosion and provide many millions of people all around the world with food, wood and an array of income opportunities.
Investments in their protection and in the restoration of destroyed marine meadows and forests therefore generate dual benefits. They help to offset emissions while simultaneously improving conditions for human communities as well as marine organisms. However, the success of planned projects depends not only on whether they are professionally designed and implemented. It is similarly critical to involve the local communities in project planning and all-important decision-making processes. Without their support, as experience from many parts of the world has shown, restoration projects on land and at sea are doomed to fail.