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Seaweed forests an overlooked ally in carbon removal

Experts are calling for greater protection of seaweed forests, which have been identified as significant contributors to oceanic carbon removal
Experts are calling for greater protection of seaweed forests, which have been identified as significant contributors to oceanic carbon removal

A groundbreaking study by an international team of researchers has revealed seaweed forests to be significant contributors to oceanic carbon removal.

Their research found that the world’s seaweed forests transport 56 million tonnes of carbon to deep ocean sinks.  

This discovery, published in the prestigious journal Nature Geoscience () highlights a considerable contribution of macroalgae to oceanic carbon sinks. The estimate represents a baseline contribution of macroalgae which, if unchanged, has a net-zero contribution to climate change mitigation. An increase in the macroalgal area through the preservation and restoration of macroalgal forests could potentially increase this contribution.

Seaweed forests, primarily composed of large brown macroalgae like kelps and rockweeds, are the most extensive and productive vegetated coastal ecosystem on the planet. These forests can grow as rapidly as terrestrial forests and are efficient in capturing carbon, which they store in their biomass. Part of the biomass is subsequently exported to deep ocean sinks, especially along coasts close to the deep sea.

The study, spearheaded by Dr Karen Filbee-Dexter at the Norwegian Institute of Marine Research and the University of Western Australia, reveals that underwater forests export about 15% of this captured carbon into deep ocean waters each year, where it can remain trapped for centuries.

The international team, which includes Prof. Michael Burrows of , used state of the art global ocean models to track the fate of seaweed carbon from the coast to the deep ocean.

“The study also identified the seaweed forests of Australia, the USA, New Zealand, Indonesia and Chile as having high carbon removal capacity,” said Dr Filbee-Dexter.

Historically, seaweed forests have been excluded from the ‘blue carbon’ toolbox due to uncertainties about their ability to remove carbon in the long-term. This study closes this critical knowledge gap and reveals new opportunities for climate change mitigation in polar and temperate areas, where carbon removal options by coastal ecosystems are currently limited.

Prof. Burrows, a co-author of the study, said: “Our work shows that damage to seaweed forests could reduce this drawdown of carbon. Conservation and restoration of such habitats for their role in carbon storage in the ocean should be a key priority.”

The study underscores the urgent need to act more quickly to protect, manage and restore seaweed forests, which are being lost at alarming rates in many regions of the world due to a variety of human pressures such as ocean warming, marine heatwaves, nutrient pollution, and overfishing.