Seagrass dates back a long time – so long that dinosaurs likely roamed the earth. Thought to have many beneficial properties, seagrass is lately receiving much praise for its role in the ocean. Yet, when it comes to this flowering marine plant, things may not be entirely as they seem.
The argument in favour of seagrass
Seagrass brings many benefits to its surrounding environment. Not least of all is the provision of protective habitat for vulnerable populations of marine creatures. For example, the short-snouted seahorse and the spiny seahorse are protected species in the British Isles that enjoy increased safe haven thanks to a four-year seagrass replanting initiative that began in April 2021. Funded by the EU LIFE program, the seagrass replanting initiative is receiving significant praise.
Seagrass plays host to a diverse cast of biodiversity; research findings suggest 40 times more animals can be found in a seagrass meadow compared with bare sand. Anemones, prawns, lobster, jellyfish and a rainbow of other kinds of fish take shelter in a seagrass sanctuary. Tiny organisms burrow into the sand around its roots, including amphipods, echinoderms, worms and more. When the tides pull out, oceangoing birds feast on stray strands of seagrass and tasty molluscs hiding therein.
What’s more, seagrass is a blue carbon habitat, meaning it stores carbon dioxide on a long-term basis. Like mangroves and salt marshes, seagrass meadows offer a carbon sink that protects the atmosphere from excessive CO2 emissions.
Flat-leaved and emerald green, around 60 different species of seagrass can be found in shallow coastal waters around the world, including along much of the coastline of the USA and Canada. Seagrass helps lock in excess nutrient run-off from mainland agriculture and stabilizes sediment, aiding mangrove growth and staving off beach erosion.
So what’s the big deal?
Despite all the positive aspects of seagrass, there are some major concerns about its contribution to greenhouse gasses across the globe.
Seagrass is, in fact, a prominent contributor of methane to Earth’s atmosphere. A report published in the February 14 edition of PNAS found that seagrass actually continues to produce methane long after the plant has died. Seagrass species including eelgrass and turtle grass (thalassia testudinum) are particularly culpable in terms of methane creation.
Researchers concluded that:
The capacity of these [dead seagrass] sediments to produce methane may persist long after the meadow die-off, thus continuing to offset the blue carbon function of these ecosystems in the long run”. Unfortunately, the CO2-sinking powers of seagrass pale in comparison to its methane gas emission.
Methane is 25 times better able to trap heat in the earth’s atmosphere than carbon dioxide, meaning runaway methane production would surely undermine the efforts of reforestation projects like Treedom. There are many far better ways to love our planet than expanding the domain of methane-pumping meadows of seagrass.
As part of the latest research findings centre on Posidonia oceanica, which grows in the Mediterranean Sea, Scientists found:
Posidonia seagrasses additionally bury large amounts of plant material in the form of massive underground peat deposits [...] a feature analogous to terrestrial peatlands, another recognized source of methane to the atmosphere.
This means that not only is methane created in the short-term during the grass’ lifetime, but even as the plant degrades into layers atop the seabed, more methane is stored for future release.
It would seem that the regular leaf loss of Mediterranean seagrass contributes to methane production. Researchers noted: “As Posidonia plants shed their leaves year-round, we speculate that the resulting leaf debris deposited on the surrounding unvegetated sediment may act as an additional and persistent source of plant-derived methane precursors.”
Much work has been done to successfully raise awareness of the global meat industry’s contribution to methane production. However, almost all of the current publicity surrounding seagrass programs is overwhelmingly positive in tone, failing to mention its methane contribution.