Restoring seagrass meadows can be a ‘triple win’ for climate, wildlife and fish

When boats full of seagrass seeds set sail off the English coast in April, it was with an ambitious agenda – to carry out England’s largest seagrass restoration project.

The goal is to plant eight hectares of seagrass meadows off the country’s southern coast over the next four years. In a massive community effort, volunteers bagged seeds at the National Marine Aquarium in Plymouth, and planters from the Ocean Conservation Trust (OCT) dropped the bags on the seabed. The seeds will eventually poke through the bags and start growing on the ocean floor. 

By Milorad Mikota – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=102000353

Seagrass matters, because – while it is thought to sequester carbon 35 times faster than a tropical rainforest – much of it has disappeared, a recent study found. The findings, though, . “should highlight the massive opportunities in restoring these habitats,” the researchers wrote in The Conversation. “Reviving the UK’s seagrass meadows could help fight the climate emergency, rebuild wildlife populations and put beleaguered fisheries back on a path to productivity.”

The newest project adds to an existing list of initiatives, including a WWF-led project that is replanting seagrass in West Wales, oysters being laid in the Durnoch Firth and coastlines being reshaped to encourage saltmarshes in Somerset, the researchers said.

But a bigger vision is needed, one comparable to a massive 20-year American project that planted thousands of hectares of seagrass off the Virginia coast. It is, so far, the world’s largest seagrass restoration project.

Researchers and volunteers planted more than 70 million eelgrass seeds over more than 200 hectares, of the southern end of Virginia’s Eastern Shore. Long-term monitoring of the restored beds reported last October shows that the seagrass is trapping carbon and nitrogen and thus offering a nature-based solution to help mitigate climate change.

Led by the Virginia Institute of Marine Science and The Nature Conservancy, the project now covers more than 3,612 hectares in new seagrass beds. One of the most interesting aspects of the US project is that the scientists were able to observe the new ecosystem from its birth to its full flowering. Seagrass in the inshore lagoons had been wiped out in the 1930s but the water was still clear so the plants could soak up sunlight.

Within the first 10 years, the ecosystem rebounded across almost every indicator — seagrass coverage, water quality, carbon and nitrogen storage, and invertebrate and fish biomass. The researchers found that seagrass meadows that were nine years or older stored, on average, 1.3 times more carbon and 2.2 times more nitrogen than younger plots, and within two decades, the restored plots accumulated carbon and nitrogen at rates similar to what natural, undisturbed seagrass beds in the same location would have stored. The beds are now sequestering on average about 3,000 metric tons of carbon per year and more than 600 metric tons of nitrogen, the researchers report.

The UK study found that while 44% or more of the UK’s seagrass has been lost since the 1930s, when it was a common sight on coasts. While this has affected both fisheries and carbon sequestration, there are still 8,493 hectares (20,987 acres) of mapped seagrass.

By Partonez – Own work, CC BY-SA 4.0, https://commons.wikimedia.org/w/index.php?curid=99488839

The scale of the loss, while immensely depressing, also underlines the massive opportunities that could come from restoring the meadows. “We estimated that the UK’s meadows once stored 11.5 million tonnes of carbon, equivalent to the annual emissions of 7.7 million cars… could also have sheltered 400 million fish, and annually filtered pollution equivalent to the amount of urine produced by the entire population of Liverpool each year.”

Business also is getting into the ‘blue carbon’ business. One Maine-based startup, Running Tide Technologies, is experimenting with farming kelp in order to ‘restore and then accelerate’ how seaweed soaks up carbon from the atmosphere. Founder Marty Odlin, who comes from generations of fishermen, is working with a team of engineers, software developers, oceanographers, maritime professionals, data scientists and hatchery technicians to bury large amounts of kelp at the bottom of the ocean. It finances its work through the sale of carbon credits to businesses which want to offset emissions.

The seeds are grown in a hatchery, and once matured, the kelp is put into biodegradable buoys. From his uncle’s re-purposed lobster boat, he and his team use ocean currents to move the kelp to deep water where it can be sunk. As they grow, the plants eventually become too heavy for the buoy, and sink to the bottom of the ocean, where the water pressure pushes the kelp into the sea floor.

Sources:

Seagrass meadows shrank by 92% in UK waters – restoring them could absorb carbon emissions and boost fish. The Conversation, Mar. 4, 2021

How planting 70 million eelgrass seeds led to an ecosystem’s rapid recovery. Science News, Oct. 14, 2020

Ocean rewilding: England’s largest seagrass restoration project gets under way. Positive News, Apr. 21, 2021

This startup grows kelp then sinks it to pull carbon from the air. CNN, May 3, 2021

The unexpected, underwater plant fighting climate change. TED Talk, Aug. 2021