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MIAMI (Reuters) - The world's seagrass meadows, a critical habitat for marine life and profit-maker for the fishing industry, are in decline due to coastal development and the losses are accelerating, according to a new study.
Billed as the first comprehensive global assessment of seagrass losses, the study found 58 percent of seagrass meadows are declining and the rate of annual loss has accelerated from about 1 percent per year before 1940 to 7 percent per year since 1990.
Published this week in the Proceedings of the National Academy of Sciences, the study, based on more than 200 surveys and 1,800 observations dating back to 1879, found that seagrasses are disappearing at rates similar to coral reefs and tropical rainforests.
"Seagrasses are disappearing because they live in the same kind of environments that attract people," James Fourqurean, a professor at Florida International University and a co-author of the study, said in an e-mailed response to questions.
"They live in shallow areas protected from large storm waves, and they are especially prevalent in bays and around river mouths."
Scientists say seagrass processes waste dumped into the sea, helps stabilize ocean-bottom sediments in coastal areas to reduce erosion, provide nurseries for fish and shellfish and feeding grounds for larger marine creatures, including those that live in coral reefs.
But the grasses can be damaged by polluted water from coastal development, decreasing water clarity, and by dredging and filling of meadows.
The scientists also said global climate change "is predicted to have deleterious effects on seagrasses." Many scientists believe greenhouse gases are causing the world to warm, leading to a host of environmental effects including warming and rising oceans.
Seagrass meadows are important food fisheries and host gamefish like tarpon, permit and bonefish.
A recent study estimated the annual economic value of seagrass at $3,500 per hectare (2.5 acres), Fourqurean said.
"Seagrass beds are at least as economically and ecologically important as tropical forests or coral reefs," he said.
The study, by a team of scientists from the United States, Australia and Spain, found that 29 percent of known seagrass meadows have disappeared since 1879. Over the entire 130-year period, seagrass was lost at a rate of 1.5 percent per year.
An estimated 19,690 square miles (51,000 square km) of seagrass has been lost since 1879 of a total estimated area of 68,350 square miles (177,000 square km), the researchers said.
"Globally, we lose a seagrass meadow the size of a soccer field every thirty minutes," said co-author William Dennison of the University of Maryland.
The scientists said 45 percent of the world's population lives on 5 percent of its land adjacent to the coast.
In the early 20th century, heavy seagrass losses were noted in North America and Europe, where the industrial revolution led to rapid coastal development.
Today, population growth in the regions bordering the Pacific and Indian Oceans are likely leading to the heaviest losses of seagrass, but those regions lack the scientific infrastructure to assess the loss, Fourqurean said.
He said mitigation efforts have had some success in saving and restoring seagrass. For example, in Florida, where treated sewage water is often dumped in the ocean, water managers in Tampa changed their method of treating wastewater and failing seagrasses rebounded.
Editing by Mohammad Zargham