Blooms of seaweed can hinder the ability of coastal seagrass to sequester carbon from the atmosphere.

Seagrass meadows act as a carbon sink, locking up carbon from the atmosphere by producing organic matter that takes a long time to biodegrade. But blooms of seaweed, largely caused by high nutrient levels due to artificial sources, can disrupt seagrass growth.

Now, a team of four researchers at Deakin University in Australia and a collaborator in China has found that seaweed blooms reduce seagrass’ ability to sequester carbon. Specifically, they found that high densities of seaweed induced microbes to decompose 20% more seagrass than normal, resulting in roughly double the emission of greenhouse gases.

This mirrors results observed in other systems where adding a source of readily decomposable carbon helps break down more resistant forms of carbon.