Mounting loss of seagrass in the world’s oceans, vital for the survival of endangered marine life, commercial fisheries and the fight against climate change, reveals a major crisis in coastal ecosystems, a report said.
A global study of seagrass, which can absorb large amounts of planet-warming carbon dioxide, found that 29 percent of the world’s known seagrass had disappeared since 1879 and the losses were accelerating.
Seagrasses are flowering plants found in shallow waters. They were vanishing at the rate of about 110km² a year since 1980, said the study to be published in the US journal Proceedings of the National Academy of Sciences.
The study by Australian and American scientists found seagrass meadows were “among the most threatened ecosystems on earth” because of population growth, development, climate change and ecological degradation.
It said there were only about 177,000km² left globally.
“Seagrass meadows are negatively affected by impacts accruing from the billion or more people who live within 50km of them,” the report said.
The study said the loss of seagrass was comparable to losses in coral reefs, tropical rainforests and mangroves.
“Seagrasses are sentinels of change” and the loss of seagrass was an indicator of a deteriorating global marine ecosystem. “Mounting seagrass loss reveals a major global environmental crisis in coastal ecosystems,” it said.
It is estimated that 70 percent of all marine life in the ocean is directly dependent upon seagrass, according to US-based Seagrass Recovery.
Seagrasses are the only flowering plants that can live entirely in water. They are most closely related to lilies and are very different to seaweeds, which are algae.
Seagrass meadows provide important ecosystem services, said the study, citing an estimated US$1.9 trillion a year in nutrient cycling, enhancement of coral reef fish productivity, habitats for thousands of fish, bird and invertebrate species and a major food source for endangered dugong and turtles.
Seagrass beds are believed to rival rice paddies in their photosynthetic productivity or the ability to extract greenhouse gas carbon dioxide and convert it into oxygen and stored carbon matter.
One acre (0.4 hectares) of seagrass can lock away nearly 8 tonnes of carbon per year, which equals the carbon dioxide emissions from a car traveling more than 5,600km, Seagrass Recovery said.
The study said more than 51,000km² of grass had been lost in the past 127 years, with the largest losses (35 percent) occurring after 1980.