Mangrove, seagrass and tidal marsh ecosystems sequester up to five times more carbon than tropical rainforests, say marine scientists who are calling for their protection.
The scientists say that because carbon dioxide (CO2) builds up not only in the plants but also in the many layers of soil underneath, coastal ecosystems harbour carbon that is thousands of years old.
"We are now learning that, if destroyed or degraded, these coastal ecosystems become major emitters of CO2 for years after the plants are removed," Emily Pidgeon, marine climate change director at Conservation International, said in a release issued Thursday.
"In the simplest terms, it's like a long slow bleed that is difficult to clot. So we need to urgently halt the loss of these high-carbon ecosystems, to slow the progression of climate change," she added.
Pidgeon is part of a panel of 32 scientists, including those from the International Union for Conservation of Nature and the Intergovernmental Oceanographic Commission of UNESCO. The panel's goal is to advance science-based management of coastal ecosystems.
The panel estimates draining a typical coastal wetland, such as a mangrove forest or a marsh, releases 0.25 million tons of C02 per square kilometre for every metre of soil that's lost.
Between 1980 and 2005, 35,000 square kilometres of mangroves were removed from coasts around the world for human development or the creation of shrimp farms. That represents an area roughly the size of Belgium.