Saltwater, sand and seagrass. On Denmark’s Thora island, in the South Funen Archipelago, is a small bay called Thurøbund. Though it might not look like much, this stretch of water is a carbon storing powerhouse. It is capable of taking in almost three times as much carbon dioxide as anywhere else recorded on the planet.
‘The bay is capable of storing 27,000 grams of carbon per square metre,’ explains ecologist Professor Marianne Holmer. This figure has never been measured to be more than 10,000 to 11,000 grams of carbon per square metre in other parts of the world – it easily outstrips all other recorded locations. ‘There’s nowhere that even comes close to Thurøbund,’ she says.
The bay’s extraordinary ability comes from an ordinary-looking source: seagrass. Though it looks a bit like seaweed, seagrass is more like a terrestrial plant. It has roots, leaves, and seed-producing flowers, and lives its whole life submerged in shallow waters. According to the report, seagrass meadows such as those found around Thurøbund are disproportionately effective at storing carbon dioxide. ‘Though they only cover a minor fraction of the seafloor, their carbon sink capacity accounts for nearly one-fifth of the total oceanic carbon burial and thus play a critical structural and functional role in many coastal ecosystems,’ write the authors of the report that discovered the findings. At Thurøbund, however, the miracle plants are also helped by geography. The bay is sheltered, meaning that when plants die they stay in place to decompose and break down, whereas on less sheltered beaches they would often be washed out to sea.
As well as their carbon storing value, seagrass meadows are an important food resource for Denmark, supporting local cod and shrimp populations. The leaves also provide shelter for juvenile fish and invertebrates. Nonetheless, Danish seagrass meadows have been reduced by 80 to 90 per cent in less than a century, and almost 30 per cent worldwide since 1879. To help support carbon storage and sustainable food production, many scientists are now calling for the protection of seagrass meadows globally.
This was published in the March 2017 edition of Geographical magazine.