About 0.1 per cent of the ocean’s floor is covered in lanky green flowering plants known as seagrasses.
Their often-sprawling meadows purify ocean water, shelter fish and provide food for thousands of marine species. But seagrass habitats have been in decline since 1930, with 7 per cent of them disappearing each year, according to United Nations Environment Programme (UNEP) research.
Along with being a haven for marine life, seagrass sediment is one of the planet’s most efficient carbon stores and prevents it from becoming a planet-warming greenhouse gas.
Now, researchers at the Max Planck Institute for Marine Microbiology in Bremen, Germany, a one-time coordinator of a European Union-UNEP project, have discovered how seagrasses store carbon.
The research shows that seagrasses convert organic carbon into large amounts of sugar during photosynthesis, mainly sucrose. Globally, seagrasses have produced between 0.6 and 1.3 million tonnes of these sugars. This is comparable to the amount of sugar in 32 billion cans of Coke.
Microorganisms usually quickly consume such sugars for food, energy and growth processes that convert the sugars into CO2 and return them to the ocean and atmosphere.
However, seagrasses excrete compounds – also found in red wine, coffee and fruit –that deter the microorganisms from consuming the sucrose. This ensures that the sucrose remains buried underneath the meadows and cannot be converted into carbon dioxide and returned to the ocean and atmosphere.
“It adds another layer to our understanding of how seagrasses are such efficient carbon sinks,” said one of the researchers, Maggie Sogin, an Assistant Professor at the University of California, Merced.
“This study is important as it offers useful lessons to policymakers and communities, helping them understand seagrasses, an underappreciated marine ecosystem,” said Leticia Carvalho, Principal Coordinator of the Marine and Freshwater Branch at UNEP. Given the sequestering power of seagrasses, Carvalho said they could play an essential role in helping countries achieve their targets under the Paris climate change agreement.
The study came out ahead of World Oceans Day. An annual event held on 8 June provides an opportunity to celebrate the importance of the underwater world and better understand how to interact with it sustainably. This year’s theme, Revitalization: Collective Action for the Ocean, puts a spotlight on ocean health, which experts say is at a tipping point.
The ocean, which covers more than 70 per cent of the planet, feeds billions, regulates the climate, and generates most of the oxygen we breathe. However, the ocean is threatened by climate change, plastic pollution, and overexploitation.
Seagrasses are found in shallow waters in 159 countries. They are increasingly imperilled by agricultural and industrial run-off, coastal development, rising sea temperatures due to climate change, unregulated fishing, and dredging, among other things. What would happen if such human activities destroyed seagrasses?
The research from the Max Planck Institute for Marine Microbiology shows that if microbes degraded the sucrose in the seagrass roots, at least 1.54 million tonnes of carbon dioxide would be released worldwide – an equivalent to the amount of carbon dioxide emitted by 330,000 cars in a year.
“This is our biggest fear,” said Sogin. “If all of the seagrasses were to disappear overnight, this would limit the ability of that ecosystem to store normally simple sugars and organic carbon. This could alter the delicate ecosystem dynamics found in our coastal waters.”
The study was carried out between 2016 and 2019 on Elba Island, Italy and the Carrie Bow Cay in Belize. Researchers hypothesise that other marine plants, including those in salt marshes, may also store sugar in their sediments.
Carvalho added, “As seagrasses are often overlooked, so too are the mesmerising and understated dugongs and manatees that call them home and rely on these meadows as a primary food source.”
There have been global efforts to map the socio-economic benefits of seagrasses and threats to them.
A new study from UNEP’s World Conservation Monitoring Centre has revealed that rising sea temperatures over the next 30 years will lead to seagrass loss in the coastal regions of Italy, Tunisia and Cyprus. The study shows that only small pockets in the south of France and the Turkish coast could “possibly escape major susceptibility to heatwaves.”
UNEP’s Out of the Blue: The Value of Seagrasses to the Environment and to People report makes recommendations on protecting and managing the habitat.
UNEP and its partners also recently launched a manual for community seagrass projects, which guides how to run a community-based seagrass conservation project.
World Oceans Day reminds every one of the major role the oceans have in everyday life. They are the lungs of our Planet and a major source of food and medicine and a critical part of the biosphere."Revitalization: collective action for the ocean" is the theme for World Oceans Day 2022, a year framed by the UN Decade of Ocean Science and the celebration of the United Nations Ocean Conference, two years after being cancelled because of the pandemic.
