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Seaweed helps to trap carbon dioxide from the atmosphere

23 May 2019

New research led by scientists from Plymouth Marine Laboratory shows, for the first time, the important role that the connectivity between macroalgae (seaweed) and the seabed plays in permanently removing carbon dioxide from the atmosphere. This has crucial implications for efforts to reduce emissions in light of the Paris Climate Agreement, and how we manage these environmentally and economically important habitats.

Seaweed on shoreline

“Blue carbon” is the carbon captured in marine systems, first by plants, through photosynthesis, and then through entrapment within the seafloor. Typically, blue carbon is linked to habitats such as saltmarshes, seagrasses and mangroves, but the potential of macroalgae, one of the ocean’s main photosynthetic organisms, and of wider sedimentary environments has often been overlooked. While the usual “blue carbon” habitats absorb and store carbon dioxide all in one location, macroalgae degrades seasonally, its detritus moving out into the coastal and open ocean, making the potential storage of this carbon unclear.

The recent study was part of the Natural Environmental Research Council (NERC) and the Department for the Environment, Food and Rural Affairs (Defra) funded Marine Ecosystems Research Programme, and also involved scientists from Florida State University, Ocean University of China and Aarhus University.

By sequencing environmental DNA and modelling stable isotope data for over a year at the Western Channel Observatory’s L4 coastal station, off the coast of Plymouth, the researchers assessed whether they could find macroalgae detritus on the sea floor, how important that detritus was to foodwebs of marine organisms and how much of the organic macroalgal carbon was trapped, or sequestered, into the sediment.

Overall, the research found that  an average of 8.75 grams of organic macroalgae carbon are sequestered per square metre of sediment every year as detrital particles, meaning that a football pitch-sized area of seabed could capture the same amount of carbon produced in driving from London to Inverness.  This one-of-its-kind study is the first to measure the importance of the coastal ocean as a potential global carbon sink and the relevance of macroalgae in trapping atmospheric carbon in the sea. With further research, this number could rise as primary areas of detritus accumulation are identified.

The study also highlighted the importance of macroalgae in supporting seabed organisms when other food resources were low through the winter months, and how these seabed dwellers also contribute to carbon sequestration; something not often considered in global “blue carbon” estimates but highlighted in two, other, recent global studies.

Dr Ana M Queirós, a Senior Benthic Ecologist at Plymouth Marine Laboratory and lead author of this paper, said: “These are the first measurements we have of seaweed carbon being sequestered into the wider seabed, beyond the narrow wetland habitats. They tell us that the global extent of blue carbon-meaningful marine habitats could be much wider than we previously thought. Identifying these areas and promoting their management will let us capitalise on the full potential of the ocean’s blue carbon towards the stabilisation of the global climate system. This is a very pressing aim, currently at the fore of national and international policy.  Protection of our marine environment and its habitats is paramount to sustainable life on our planet.

Related information

The paper ‘Connected macroalgal-sediment systems: blue carbon and foodwebs in the deep coastal ocean’ is published this week in Ecological Monographs.

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