Jul 10, 2020 - Energy & Environment

Seagrass is good at storing CO2, but it's vanishing

A seagrass meadow. Photo: Centre for Marine Ecosystems Research at Edith Cowan University

A seagrass meadow. Photo: Centre for Marine Ecosystems Research at Edith Cowan University

Meadows of seagrass on the ocean floor are among the planet's most efficient ecosystems for absorbing and storing carbon.

Why it matters: Climate change, industrial and agricultural run-off, and development along coastlines are threatening the world's seagrass meadows.

  • About 161,150 hectares of seagrass have been lost along Australia's coasts since the 1950s, releasing carbon dioxide equivalent to that from 5 million cars each year, according to new research.

What they did: Cristian Salinas of Edith Cowan University and his colleagues compared carbon stored in the sediment of seagrass meadows with areas that no longer had seagrass in western Australia's Cockburn Sound.

  • A loss of seagrass by itself didn't account for the carbon dioxide emitted from the soil, the researchers report in the journal Global Change Biology.
  • Waves, tides and currents disrupted the soil and sand in shallow areas without seagrass, releasing the carbon sequestered in it.
  • They also found seagrass meadows in shallow water stored more carbon than those in deep water, making the nearshore an important area to preserve, Salinas notes.

The big picture: Seagrass meadows — made up of more than 70 species of the marine flowering plant — filter seawater, buffer ocean acidification, regulate carbon and are home to more than 20% of the world's largest fisheries.

  • "In one square meter is the same amount of carbon that can be sequestered in 30-40 square meters of forest," says Salinas.
  • About 7% of the habitat is lost each year, contributing up to 299 Tg of carbon to the atmosphere, according to a June report from the U.N. Environment Programme.
  • The U.N. and others are urging countries to preserve and restore seagrass as one way to address climate change.
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