In the world’s largest seaweed restoration project, scientists observed an ecosystem from birth to full bloom.
As part of a more than 20-year project, researchers and volunteers spread more than 70 million eel seeds on plots of more than 200 acres, just beyond the vast expanses of salt marsh off the south end of Virginia’s east coast. Long-term control of restored seagrass beds reveals a highly resilient ecosystem that traps carbon and nitrogen that would otherwise contribute to global warming and pollution, the team reported on Oct. 7 in Science Advances. That success provides a glimmer of hope for the climate and ecosystems, the researchers say.
The project, led by the Virginia Institute of Marine Sciences and The Nature Conservancy, has now grown to cover 3,612 acres – and counting – in new marine beds. In comparison, the largest such project in Australia aims to restore 10 hectares of seagrass.
The results are “a game changer,” says Carlos Duarte. “It’s an example of how nature-based solutions can help mitigate climate change,” he says. Marine ecologist at King Abdullah University of Science and Technology in Thuwal, Saudi Arabia, is a leader in recognizing the carbon storage capacity of mangroves, marshes and marine grasses.
The Virginia team started with a blank board, says Robert Orth, a marine biologist at the Virginia Institute of Marine Sciences at Gloucester Point. The seagrass in these coastal lagoons had been wiped out by disease and a hurricane in the early 1930s, but the water was still clean enough to transmit the sunlight the plants require.
Within the first 10 years of restoration, Orth and colleagues witnessed a rapidly bouncing ecosystem in almost every indicator of ecosystem health: grass cover, water quality, carbon and nitrogen storage, and invertebrate and fish biomass ( SN: 16/02/17).
For example, the team monitored the amount of carbon and nitrogen the meadows captured from the environment and stored in the sediment as the cover of seagrass expanded. He found that meadows in place for nine or more years stored, on average, 1.3 times more carbon and 2.2 times more nitrogen than younger plots, suggesting that storage capacity increases as the meadows mature. meadows. In 20 years, the restored plots were accumulating carbon and nitrogen at a rate similar to that which would store natural beds and without disturbance of seagrass in the same place. Restored marine herb banks now sequester an average of about 3,000 tons of carbon a year and more than 600 tons of nitrogen, according to researchers.
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Seaweeds can have a blow. When a sudden wave of sea heat killed part of the seagrass, the meadow took only three years to regain its plant density. “We were amazed at how resilient these seagrass meadows were,” says Karen McGlathery, a coastal ecologist at the University of Virginia in Charlottesville.
She believes teamwork is more than just a good case study in restoration. “It offers a plan to restore and maintain healthy marine herb ecosystems” that others may adapt elsewhere in the world, she said.
Marine herbs are among the most valuable and endangered ecosystems in the world and are important globally as reservoirs of what is known as blue carbon, the carbon stored in oceanic and coastal ecosystems. Marine herbs store more carbon, for much longer, than any other terrestrial or oceanic habitat, preventing it from escaping into the atmosphere as carbon dioxide that traps heat. These underwater prairies also support inshore and coastal fishing and protect the coasts and other marine habitats. Despite their importance, marine herbs have declined by 30% worldwide since 1879, according to a study conducted Aug. 14 in Frontiers in Marine Science.
“The study helps fill large gaps in our understanding of how blue carbon can contribute to climate restoration,” McGlathery says. “It’s the first to put a number of how many restored carbon meadows take out of the atmosphere and store,” for decades and potentially for centuries.
The restoration is far from over. But it may already point the way to troubled ecosystems such as Florida Bay of Biscayne, which was once rich in seaweed but now suffers from water quality degradation and extensive fish death. Once the water is cleaned, Orth says, “our work suggests that seaweeds can recover quickly” (SN: 5/5/18).
McGlathery also believes the scale of team success should be uplifting for coastal communities. “In my early years here, there was no seaweed and there weren’t decades. Today, as far as I can swim, I see lush meadows, rays, the occasional seahorse. It's beautiful."