The coastal landscape affects seagrass meadows' ability to mitigate climate change
Seagrass meadows have a fantastic ability to store carbon dioxide. A new study from the University of Gothenburg shows that the composition and properties of the surrounding landscape affect the meadows' storage capacity. This knowledge makes it easier to identify and preserve high-capacity meadows and thus avoiding the release of greenhouse gases into the atmosphere.
“Coastal ecosystems such as seagrass meadows, salt marshes, and mangrove forests have proven to be much more efficient at storing carbon dioxide than most forests on land. That’s why we’ve studied how the landscape's configuration affects the meadows’ ability to build up carbon dioxide sinks,” says Maria Asplund, researcher at the Department of Biology and Environmental Science and active at Kristineberg Marine Research Station.
“Factors that affect the storage capacity are what the coast looks like, what habitats there are, the size of the seagrass meadow, the proximity to land and the open sea and nearby environments such as mangrove forests,” Maria Asplund continues.
The study was conducted in Tsimipaika Bay on the northwest coast of Madagascar in a broad collaboration between local universities, non-profit organizations in Madagascar, international institutions in Tanzania, Australia, Spain, and Portugal together with Swedish researchers at the University of Gothenburg, Stockholm University, and Södertörn University. By taking samples of the seabed, the researchers can determine how much carbon is bound in the sediments of the seagrass beds.
“It is not just the seaweed itself that binds carbon dioxide from the atmosphere. The seagrass meadow's complex three-dimensional structure is good at trapping particles in the water and thus absorbing organic material that comes from other ecosystems and then storing the carbon in the sediment.”
The sediments are low in oxygen which means that the decomposition of the material is slow and the carbon can therefore be stored for a long time, thus buffering against global warming.
The key to preserving the potential of seagrass meadows
Today, between two and seven percent of the oceans' carbon sinks are destroyed every year. The mangrove forests and the salt and seagrass meadows are destroyed five to ten times faster than the rainforest. By better understanding where in the landscape the storage capacity is greatest, areas with great potential, so-called hotspots, can be identified and protected.
“It is very complex, many factors affect the storage capacity. Our study shows that large seagrass meadows tend to have a better ability to store carbon. We found that meadows that have a more complex 3D structure with long seagrass are better at capturing carbon from other areas. We also saw that seagrass beds closer to mangrove areas contain more organic material that originates from the mangrove forest and other land plants. This became even clearer in areas where the mangroves have been felled in recent decades. This shows important connections between different habitats that affect the storage capacity.”
“It’s not enough to look at the properties of the seagrass meadows themselves. We need to look at how the whole landscape is configured and what is happening in the immediate area, otherwise we might miss factors that are important for the storing of carbon dioxide. It is important to understand all the ecosystem services that seagrass meadows provide, not only that they preserve biodiversity or offer a coastal protection function, but also its climate-compensating ability.”
If the seagrass meadows disappear, greenhouse gases can be released and contribute to global warming.
“There is a very high risk that the stored carbon is emitted as carbon dioxide if the seagrass meadows disappear. You can also get emissions of other powerful greenhouse gases such as methane and nitrous oxide.”
There is also great potential for carbon dioxide storage in the sediment of Swedish seagrass meadows.
“We do similar studies here at Kristineberg and we have found that our seagrass meadows have a high potential to store large amounts of carbon. We see that the carbon storage capacity here is close to the highest measured levels in the world. We have ongoing studies to identify hotspots that can be particularly effective carbon sinks.”
The month of March has been named Seagrass Awareness Month to bring attention to the importance of seagrass.
“Seagrass meadows and their importance are relatively unknown to the public as they grow in aquatic environments that many people never have the opportunity to see. The meadows constitute important habitats for many organisms and growing areas for fish. They also act as protection against coastal erosion and are important natural carbon sinks that help to counteract climate change. Seagrass meadows are one of the coastal habitats that are most worthy of protection, but despite this, seagrass meadows in the world have decreased sharply. They are mostly located in coastal areas that are used by humans, so they have to compete with a lot of human activities. Therefore, it is important that we pay attention to the importance of seagrass meadows so that we are careful about these important environments,” says Maria Asplund.
Read the full study:
Dynamics and fate of blue carbon in a mangrove–seagrass seascape
Text: Simon Ungman Hain