impact

Seagrass—secret weapon in the fight against global heating

One of the most threatened yet overlooked ecosystems on Earth, seagrass could have a promising future thanks to its ability to absorb carbon.

Seagrass is a flowering marine plant whose blades form dense meadows in shallow, sheltered areas along coastlines. It has a range of benefits: seagrass acts as a nursery and food source for a wide variety of marine life, provides a home for many fish and charismatic animals such as turtles and dugongs, protects coastlines by absorbing wave energy, produces oxygen and cleans the ocean by soaking up polluting nutrients produced on land by humans.

In addition, seagrass accounts for 10 per cent of the ocean’s capacity to store carbon—so-called “blue carbon”—despite occupying only 0.2 per cent of the sea floor, and it can capture carbon from the atmosphere up to 35 times faster than tropical rainforests.

According to The Ocean as a Solution to Climate Change: 5 Opportunities for Action, published by the World Resources Institute, while the mitigation potential per unit area of restoring seagrasses is relatively high, though not as high as for restoring saltmarshes or mangroves, the mitigation potential of seagrass conservation is exceptionally high, and much higher than that of saltmarshes and mangroves.

A dense seagrass meadow of the little Neptune grass in Greece Photo by Dimitris Poursanidis/GRID-ArendalA dense seagrass meadow of the little Neptune grass in Greece. Photo by Dimitris Poursanidis/GRID-Arendal

However, it’s important to understand that there are many unknowns with seagrass.

“Data on the regional cover and carbon stocks in seagrass meadows is sparse for some regions, particularly the Indo-Pacific, Africa and South America,” says a report titled Assessing the capacity of seagrass meadows for carbon burial: Current limitations and future strategies.

“In addition, our understanding of the factors regulating the variability in carbon sink capacity among seagrass meadows is limited. These gaps limit the capacity to formulate strategies to mitigate climate change based on the carbon sink capacity of seagrass meadows,” the report adds.

Nevertheless, the potential of seagrasses to sequester carbon is now starting to gain international attention as efforts to tackle the climate emergency become ever more urgent. The latest report by the Intergovernmental Panel on Climate Change, focusing on oceans and the cryosphere, points out that mangroves, salt marshes and seagrass meadows can store up to 1,000 tonnes of carbon per hectare—much higher than most terrestrial ecosystems.

Meeting climate commitments

Restoration of these habitats can count towards national climate-change plans. Each signatory to the Paris Agreement is required to submit its plan, or nationally determined contribution, to the United Nations, with successive plans becoming more ambitious.

The potential for seagrass in nationally determined contributions is significant, as some 159 countries have seagrass on their shores. An analysis soon to be published by GRID-Arendal, a Norwegian foundation working with the United Nations Environment Programme (UNEP), found that 10 countries have included seagrass in existing nationally determined contributions. Five countries refer to its conservation and restoration in mitigation actions, while eight plan to use it in adaptation.

Researcher doing field work in a seagrass meadow Photo by Dimitris Poursanidis/GRID-ArendalResearcher doing field work in a seagrass meadow. Photo by Dimitris Poursanidis/GRID-Arendal

“There is clearly a great missed opportunity here, and the potential for more countries to include seagrass as part of their box of tools for mitigating and adapting to climate change,” says UNEP marine ecosystems expert Gabriel Grimsditch.

“Seagrass meadows are rapidly disappearing in many parts of the world,” he adds. “The impact of the one billion or more people who live within 50 km of them is largely the cause, including damage from coastal development and degraded water quality from nutrient pollution. Annual rates of decline have accelerated, with loss rates comparable to those of coral reefs and tropical rainforests.”

UNEP, GRID-Arendal and the UNEP-World Conservation and Monitoring Centre have convened the International Seagrass Experts Network and plan to launch a global report on the importance of seagrass ecosystems in early 2020.

Scaling up seagrass restoration

Meanwhile, countries including the United States and Sweden have been experimenting with seagrass restoration for several years. And a team in the United Kingdom is about to embark on the largest seagrass restoration project ever undertaken in its waters.

However, restoration is tricky and expensive. Evidence suggests that the bigger the project is, the more chance there is of success—if the project is too small, it’s very susceptible to damage. UNEP and the Nairobi Convention will be launching a manual on seagrass restoration for the Western Indian Ocean in the near future.

“Humans do not yet have long-term experience of planting at sea, in contrast with our many centuries of experience on land. Wherever possible it’s better to conserve what we already have,” says Grimsditch.

The UN Decade on Ecosystem Restoration 2021–2030, led by the UN Environment Programme, the Food and Agriculture Organization of the United Nations and partners such as Afr100, the Global Landscapes Forum and the International Union for the Conservation of Nature, covers terrestrial as well as coastal and marine ecosystems. A global call to action, it will draw together political support, scientific research and financial muscle to massively scale up restoration. Help us shape the Decade.

For more information, please contact Gabriel Grimsditch: [email protected]