New study: Seagrass meadows have stored carbon for 4,000 years – climate benefit that cannot be recreated
Beneath the surface of the Baltic Sea, there are ecosystems that have stored carbon and nitrogen for thousands of years. Seagrass meadows, often overlooked or unknown, function as long-term carbon sinks and are vital to both the climate and marine ecosystems. New research shows that these underwater meadows are considerably older – and more irreplaceable – than previously thought.
Researchers have analysed the sediments (layers of seabed) beneath eelgrass (Zostera marina) meadows to track how carbon and nitrogen have been stored in the seabed over several millennia. Their findings show that seagrass was established over 4,000 years ago, and again around 1,700 years ago, when land uplift created calmer and more sheltered coastal environments.
“This is not something that’s built up over a few decades. We’re talking about carbon sinks that are thousands of years old,” says Martin Dahl, an associate professor and one of the researchers behind the study published in the prestigious journal Nature. External link.
Built up over millennia
Seagrass meadows can be compared to forests on land – it takes an extremely long time to build their structure and function, and when they are destroyed it’s not only the plants that vanish, but an entire ecosystem that has stored carbon for generations. And, just like land-based forests and meadows, they are complex and species-rich environments that require stable conditions and long periods of continuity. They provide habitats for fish and small animals, stabilise bottom sediments and help to create a healthier coastal environment.
Restoration is inadequate
Research also shows that the importance of seagrass meadows extends beyond the meadows themselves. Organic matter spreads to the surrounding seabed and contributes to further carbon and nitrogen sequestration, much like a form of long-term ecological memory in the coastal landscape.
Against this background, the message is clear: conservation is more important than restoration.
“There is a belief that we can always recreate what has been lost. But when it comes to seagrass, we are talking about ecosystems that have developed over thousands of years, so protection is absolutely crucial,” says Dahl.
Preserving seagrass meadows is thus more than a matter of nature conservation. It is a way to protect an underwater heritage and a climate service that stretches a long way back in time.
About the report
By drilling into the seabed beneath the seagrass meadows, researchers been able to analyse historical layers of organic material using sediment cores. The samples come from the archipelago off Västervik. The study has been published on Nature.com/Scientific Reports, and the research is funded by the Foundation for Baltic and East European Studies and FORMAS.
New study: Seagrass meadows have stored carbon for 4,000 years
- Seagrass meadows in the Baltic Sea have stored carbon and nitrogen for more than 4,000 years
- They function as underwater forests – biodiverse ecosystems that take thousands of years to develop
- When they are destroyed, the plants are not all that is lost – it is an entire ecosystem and a climate heritage
- The conclusion is clear: conservation is more important than restoration – the climate benefit cannot be recreated
- The study is published in Nature/Scientific Reports
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- 2026-07-03
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