Although seagrasses account for less than 0.2% of the world’s oceans, they sequester approximately 10% of the carbon buried in ocean sediment annually (27.4Tg of carbon per year). Per hectare, seagrasses can store up to twice as much carbon than terrestrial forests.
“By all accounts they are a miracle of the underwater world. Reckoned to sequester carbon 35 times faster than a tropical rainforest, seagrass meadows also provide a haven for some of the most fantastical marine creatures on Earth – even in the UK, where enigmatic seahorses are among those found sheltering in the swaying blades.” Gavin Haines of Positive.News wrote these words on April 21, 2021, as an unprecedented restoration project got underway that day in the south coast of England.
Planters from the Ocean Conservation Trust (OCT) dropped canvas bags containing seagrass seeds on the seabed. Over time the seeds inside the bag will “poke through the canvas and start recolonizing the ocean floor.” The efforts were led by Natural England, the LIFE Recreation ReMEDIES project with help from local volunteers. Another rewilding project in the UK, Project Seagrass, planted over two hectares of seagrass seeds last year along the coast of Pembrokeshite, Wales.
The plan is to restore twelve hectares of depleted underwater meadows in Plymouth Sound and Solent Maritime Special Area of Conservation over the next four years. According to some estimates over 90% of the UK’s seagrass meadows have vanished from pollution, dredging, bottom trawling and coastal developments.
The Blue Carbon Initiative
Blue carbon ecosystems include mangroves, tidal marshes, and seagrass meadows.
Mangroves are among the most carbon-rich forests in the tropics and estimated to sequester on average 6-8 mg CO2e/ha—about four times greater than global rates observed in mature tropical forests. About 30-50% of mangroves have been lost globally in the last 50 years and continue to be lost at a rate of 2% each year due to deforestation for construction of aquaculture ponds and other forms of unsustainable coastal development.
Tidal marshes, which are coastal wetlands with deep soils created through the accumulation of mineral sediment and organic material, sequester 6-8 Mg CO2e/ha—about 2 to 4 times greater than those observed in mature tropical forests. Tidal marshes filter pollutants from land runoff, helping to maintain water quality in coastal areas. They provide critical habitat for many stages of marine life; they absorb energy from storms and floods, helping to buffer the coast and prevent erosion. They are being lost at a rate of 1-2% through draining for coastal development, conversion to agriculture, and rising sea levels.
Seagrasses are found in meadows along the shores of every continent except Antarctica. Per hectare, seagrasses store up to twice as much carbon as terrestrial forests. Seagrass meadows filter sediment and other nutrients from water; they constantly build and secure sediment, buffering coasts from storms, flooding and erosion. They contribute habitats for a diversity of marine species and are among the most threatened ecosystem in the world. Global loss is 1.5% with a third of Earth’s seagrass ecosystems lost from pollution, land use, deforestation and dredging.
“The coastal ecosystems of mangroves, tidal marshes, and seagrass meadows provide numerous benefits and services that are essential for climate change adaptation along coasts globally, including protection from storms and sea level rise, prevention of shoreline erosion, regulation of coastal water quality, provision of habitat for commercially important fisheries and endangered marine species, and food security for many coastal communities. Additionally, these ecosystems sequester and store significant amounts of coastal blue carbon from the atmosphere and ocean and dense are now recognized for their role in mitigating climate change.”—TheBlueCarbonInitiative.org
“Despite these benefits and services, coastal blue carbon ecosystems are some of the most threatened ecosystems on Earth, with an estimated 340,000 to 980,000 hectares being destroyed each year. It is estimated that up to 67% and at least 35% and 29% of the global coverage of mangroves tidal marshes and seagrass meadows respectively have been lost. If these trends continue at current rates, a further 30–40% of tidal marshes and seagrasses and nearly all unprotected mangroves could be lost in the next 100 years. When degraded or lost, these ecosystems can become significant sources of the greenhouse gas carbon dioxide.”—TheBlueCarbonInitiative.org
Blue carbon ecosystems mitigate climate change by sequestering carbon dioxide from the atmosphere and oceans at significantly her rates, per unit area, than terrestrial forests. The carbon deposits are stored aboveground in the biomass of plants (tree trunks, stems, and leaves), below ground in the plant biomass (roots and rhizomes), and in the carbon-rich organic soils of these coastal ecosystems. Fifty to ninety-nine percent of the stored carbon is located in the soils below ground. These rich soil carbon stores can be up to six meters deep below the surface, where it can remain for a very long time—millennia.
Nina Munteanu is a Canadian ecologist / limnologist and novelist. She is co-editor of Europa SF and currently teaches writing courses at George Brown College and the University of Toronto. Visit www.ninamunteanu.ca for the latest on her books. Nina’s bilingual “La natura dell’acqua / The Way of Water” was published by Mincione Edizioni in Rome. Her non-fiction book “Water Is…” by Pixl Press(Vancouver) was selected by Margaret Atwood in the New York Times‘Year in Reading’ and was chosen as the 2017 Summer Read by Water Canada. Her novel “A Diary in the Age of Water” was released by Inanna Publications (Toronto) in June 2020.