New research increases understanding of how seagrass meadow ecosystems function

One of the most important nearshore marine ecosystems absorbs carbon dioxide, but its potential to release methane – even after death – has been underestimated.

Scientists at the Max Planck Institute for Marine Microbiology have published the results of a major investigation into seagrass meadows, and specifically how they produce one of the most damaging greenhouse gases, methane. 

It had previously been assumed that seagrass meadows produced the gas in the same way grass on land does – through large peat deposits formed below the ground’s surface, triggering decomposition of organic material.

However, methane actually results from a single type of organic compound, known as methylated compounds. These include betaine, which helps seagrasses cope with changes to salt levels in water. Specialised microorganisms, methanogenic archaea, then convert this directly into methane. 

The process is highly efficient, and robust to environmental changes, which are most pronounced in the coastal regions where seagrasses are found. The grass itself also acts as a straw-type device, making it easier for methane to escape the seabed, while the tide contributes further still, ‘washing out’ methane from surface sediment.

This means methane production and spread is significantly faster in seagrass than on land. The study also found methane continues to be produced by marine meadows long after the grass has died. In contrast, its ability to capture carbon dioxide will stop.

‘Currently, we are seeing a die-off of seagrass meadows worldwide which has a devastating effect on the coastal ecosystems. Our results caution that whereas upon the death of the plant carbon dioxide from the atmosphere will no longer be sequestered and stored in the sediment as ‘blue carbon’, methane may still continue to be released,’ said Jana Milucka, senior author of the study and head of the Greenhouse Gases Research Group at the Max Planck Institute for Marine Microbiology. 

The team consider this a significant step towards understanding how seagrass meadow ecosystems function, which support a broad range of life, including several endangered species such as sea turtles, seahorses, and many types of fish. Work in this area will, in turn, help better measure the impact caused by the destruction of these habitats. 

Image credit: Benjamin L. Jones