Shrinking sea meadows store more carbon than forests. Scientists are racing to track what’s left
Hundreds of miles from the nearest shore, ribbon-like fronds flutter in the ocean currents sweeping across an underwater mountain plateau the size of Switzerland.
A Greenpeace team free dives in the turquoise waters of this corner of the western Indian Ocean capturing rare footage of what scientists believe is the world’s largest seagrass meadow.
The Arctic Sunrise ship sailed for days in March to reach the Saya de Malha bank on a research expedition to collect some of the first field data on the region’s wildlife, including its little-studied beds of seagrass.
The Saya de Malha poses a challenge for field research because of its size and isolation. Its waters are relatively uncharted and visitors by boat must navigate wildly varying depths that cause unusual swells and currents.
While most seagrasses fringe coastlines around the world, the shallowness of Saya de Malha allows sunlight to filter to the seabed, creating an aquatic prairie in the Indian Ocean that provides shelter, nurseries and feeding grounds for thousands of marine species.
“Because it’s so large it most likely has quite a large contribution to climate change mitigation and acts as quite a valuable climate carbon sink,” said the lecturer in Ecology at the University of Exeter and consultant for Greenpeace’s Protect the Ocean campaign, Dr Kirsten Thompson.
Seagrasses play a large role in regulating ocean environments, capturing more than twice as much planet-warming carbon dioxide (CO2) per square mile as forests do on land, according to a 2012 study in the journal Nature Geoscience.
The grasses also curb the acidity of surrounding waters — an especially important function, as the ocean absorbs more CO2 from the atmosphere and becomes more acidic.
Data on where seagrasses grow are patchy, but scientists estimate the grasses cover around 300,000 square km, an area the size of Germany, distributed across all continents apart from Antarctica, according to UNEP.
It is not yet known how much carbon is locked into Saya de Malha, but globally the tangled roots of seagrasses are estimated to hold more than 10 percent of the carbon buried in ocean sediment per year.
“Protecting these areas is one way of making sure that we’re not making the climate emergency worse but also we have that ability and that valuable ecosystem in the future for future generations,” said Thompson.
Seagrass stocks are believed to be retreating around 7 percent per year globally, according to the most recent global seagrass census published in a 2009 study in Proceedings of the National Academy of Sciences. It notes that the estimate was based on incomplete datasets available at the time.
If still intact, these could have supported around 400 million fish and stored 11.5 million tonnes of carbon — the equivalent of 3 percent of Britain’s CO2 emissions in 2017, the study said.
As the international community struggles to bring down emissions and curb climate change, countries are now looking to seagrasses for help.
The 2015 Paris Agreement invites countries to include seagrass conservation in their pledges to reduce emissions.