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A natural solution to reducing plastic from the ocean: seagrass

What’s happening? Underwater seagrass meadows may be naturally trapping millions of fragments of marine plastic and removing them from the oceans, according to a study from the University of Barcelona. Fibres in the leaves shed by the Posidonia oceanica seagrass, endemic in the Mediterranean and found in coastal waters up to 40 metres deep, create tangles known as Neptune balls that can trap the plastic, the study reveals. When the balls are ejected from the sea during storms, they also return the plastic to the shore. Plastic items were also found in 50% of the loose leaves sampled.

Why does this matter? This novel ecosystem service provided by seagrass meadows could aid efforts to combat plastic pollution in oceans, which not only affects the growth and survival of marine species, but also food webs and human health.

The broader picture – The world’s oceans contain around 150 million mt of plastic, with an additional eight million mt added each year. The scale of microplastic pollution has in the past been significantly underestimated and plastics have been found at levels at least twice as high as previously reported. Although high-level commitments to reducing some plastic items are gaining traction from countries such as China and the UK, removing plastics already in global waters on a large scale has not yet been addressed.

Nature-based plastic traps – The University of Barcelona study found high concentrations of plastic debris present in 17% of the Neptune balls sampled, reaching up to 1,470 plastic items per kg of seagrass. Neptune balls are formed when lignocellulosic fibres from seagrass leaf sheaths are released, which can interlace with plastics when the ball-shaped clusters are shaped.

Researchers estimate that Neptune balls could trap up to 867 million items of plastic debris in the Mediterranean annually. The plastic-trapping ability of seagrass, however, could be hindered by shrinking seagrass ecosystems. At least 22 of the world’s 72 seagrass species are in decline from threats including climate change, unregulated fishing practices and pollution.

Could this aid the global plastic problem? Possibly, so long as efforts are made to conserve seagrass habitats. A seagrass restoration project in the UK, for instance, aims to restore eight hectares of lost seagrass around UK waters by initially cultivating the plants in a laboratory.

The potential for seagrass meadows in other locations to provide similar functions to gather and trap plastic – such as related species near the coast of Australia – remains unclear. Elsewhere, a study by the Plymouth Marine Laboratory is underway to explore the natural feeding process of mussels as another natural solution. The project, funded by Waitrose’s Plan Plastic: The Million Pound Challenge, will investigate whether “bioreefs” of mussels could be harnessed to remove microplastics from marine environments.

Lateral thought from Curation ­– Artificial machines are being designed to address ocean plastic, such as the Ocean Cleanup device, which aims to remove 90% of plastic using a screen attached to a floating barrier. Research, however, has recently claimed one of these devices will only succeed in removing a fraction of 1% of ocean plastic by 2150. The case for natural solutions could be bolstered, therefore, if they are found to be more effective than technology.

Similarly, “Citytree” machines have been installed in some urban areas in the UK to improve air quality. These have drawn criticism for essentially trying to reinvent the tree, while other cities have looked to address the problem by simply planting trees themselves. Seoul, for instance, will introduce “wind path forests” across the city to channel clean air and reduce air pollution through air-purifying plants.

Katie Chan

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