Loss of seagrasses 'accelerating'
Nearly 30% of global seagrass beds have been lost since records began, and the rate of loss is accelerating, according to a new study.
Marine biologist Professor Gary Kendrick, of the University of Western Australia in Perth, and colleagues report their findings this week in the Proceedings of the National Academy of Sciences.
"The losses have been quite substantial," says Kendrick. "Every year we're losing about 110 square kilometres of seagrasses globally."
He and colleagues found that since 1980, 29% of seagrass has disappeared and the overall rate of loss has accelerated from 0.9% a year, before 1940, to 7% a year, since 1990.
In the largest study of its kind, Kendrick and colleagues analysed 215 studies of seagrass beds in shallow coastal waters from around the world.
They found seagrass is being lost from east and west North America, the Caribbean, Mediterranean, Europe, parts of East Asia, Southeast Asia, as well as tropical and temperate Australasia.
Nutrient culprit
Nutrients in sewage and run-off from agriculture and industry are the major cause of seagrass death, says Kendrick.
These nutrients trigger the growth of algae, plants and animals that grow above or on seagrass, and stop it from getting the sunlight it needs.
"In Western Australia, in Cockburn Sound, we've lost 80% of our seagrasses. Over 1200 hectares of seagrasses have been lost in the last four decades," says Kendrick.
"The loss of seagrass there can be tied directly to nutrient input in the form of nitrogen."
Lungs of the ocean
Kendrick says the rate of seagrass loss is comparable to the loss of tropical rainforest.
He says studies have found seagrass fixes as much carbon dioxide as tropical forests, and is also a crucial part of the ocean food chain.
About 75% of seagrass feeds bacteria, which are the bottom of the ocean food chain, says Kendrick: "They actually feed the whole food web."
He says the other 25% of seagrass is eaten directly by animals such as dugongs, green turtles, fish, snails and crustaceans, as well as birds like geese and swans.
