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Shrinking sea grasslands add carbon emissions concerns

Hundreds of kilometers from the nearest coast, ribbon-shaped fronds float in ocean currents sweeping an underwater mountain plateau the size of Switzerland.

A remote-controlled camera glides through the turquoise, sunny waters of this corner of the western Indian Ocean, capturing rare footage of what scientists consider to be the world’s largest seagrass prairie.

Human activity contributes to destroying the equivalent of a football field of these grass beds every 30 minutes around the world, according to the United Nations Environment Program (UNEP). And scientists are now rushing to take stock of what remains.

“There are a lot of unknowns – even things as simple as how much seagrass we have,” said Gwilym Rowlands, an Earth Observation Specialist at the University of Oxford, who helps the government of Seychelles to map the island nation’s seagrass beds and estimate the amount of carbon it stores.

“If you look at the seagrass map data, there are huge holes” in what we know.

According to a 2012 study by the journal Nature Geoscience, seagrass beds play an important role in regulating ocean environments, storing more than twice as much carbon from the warming carbon dioxide (CO2) (CO2) per square mile. than forests on earth.

Countries hoping to obtain a credit to reduce their CO2 emissions could count their herbaria and the carbon they store, a first step towards accreditation of carbon offsets for possible trade in an open market.

Herbs also reduce the acidity of surrounding waters – a particularly important function as the ocean absorbs more CO2 from the atmosphere and becomes more acidic.

But sea grasses provide some protection against acidification, which can damage animal shells and disrupt fish behavior. In a study published March 31 in the journal Global Change Biology, scientists at the University of California at Davis found that sea grasses scattered along the California coast could reduce local acidity by up to 30% for up to 30%. long periods.

Plants also help clean polluted water, support fishing, protect coastlines from erosion and trap microplastics, said lead author Aurora Ricart.

“What’s even cooler is that these habitats are everywhere,” she says.

While most seagrass beds line coastlines around the world, the shallow depth of Saya de Malha allows sunlight to filter through the seabed, creating an aquatic grassland in the Indian Ocean that provides shelter, nurseries and feeding grounds for thousands of marine species.


The bank’s isolation has helped protect it from coastal threats, including pollution and dredging. But even such distant international waters are facing increasing inroads from shipping and industrial fishing.

In March, scientists from institutions such as the British University of Exeter traveled with Greenpeace as part of an expedition to collect some of the first field data on the region’s wildlife, including its little-studied seagrass beds. .

As the boat floated for days above the plateau, researchers gathered pieces of grass floating in the water, pinching them into bottles for analysis on shore.

Data on seagrass beds are sketchy, but research so far estimates that grasses cover more than 300,000 km2 (115,000 square miles), spread across all continents except Antarctica, according to UNEP. . It would be a region the size of Italy.

It is not yet clear how much carbon is trapped in Malha’s Saya, but globally, it is estimated that the tangled roots of seagrass trap more than 10 percent of the carbon buried in ocean sediments per year.

“This has massive implications for climate change mitigation efforts (around the world),” said Dimos Traganos, senior scientist on a German Aerospace Center project developing software to improve seagrass monitoring at the using satellite images and other data. This effort has been facilitated by recent advancements in cloud computing and data storage, he said. “We are in such an exciting time.”

Seagrass beds are thought to be declining by around 7% per year globally, according to the latest seagrass census published in a 2009 study in Proceedings of the National Academy of Sciences. He notes that the estimate was based on incomplete data available at the time.

The most studied areas illustrate the damage that human activity can cause. Pollution from mining and fishing damage may have helped wipe out 92% of mainland Britain’s seagrass beds, according to a study published March 4 in the journal Frontiers in Plant Science. of a century.

If still intact, these could have supported around 400 million fish and stored up to 11.5 million tonnes of carbon percentage, or 3% of Britain’s CO2 emissions in 2017, according to study.

This year, Seychelles began to assess the carbon stock of their coastal seagrass for the first time, and at least 10 countries have said seagrass beds will play a role in their climate action plans, according to UNEP.

Seychelles and Mauritius, which have joint jurisdiction over the Saya de Malha seabed, should rely on and take care of the rich seagrass beds at their common doorstep, said James Michel, who served as President of Seychelles for 12 years until ‘in 2016.

“Then we will be in a better position to know not only how to preserve it, but also to manage it to ensure that it will be optimized for the future.”

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