February 16 2017 Carl Zimmer NY Times Full article here
Every continent save Antarctica is ringed by vast stretches of seagrass, underwater prairies that together cover an area roughly equal to California.
Seagrass meadows, among the most endangered ecosystems on Earth, play an outsize role in the health of the oceans. They shelter important fish species, filter pollutants from seawater, and lock up huge amounts of atmosphere-warming carbon.
The plants also fight disease, it turns out. A team of scientists reported on Thursday that seagrasses can purge pathogens from the ocean that threaten humans and coral reefs alike. (The first hint came when the scientists were struck with dysentery after diving to coral reefs without neighboring seagrass.)
But the meadows are vanishing at a rate of a football field every 30 minutes. Joleah B. Lamb, a postdoctoral researcher at Cornell University and the lead author of the new study, said she hoped it would help draw attention to their plight….
…The plants also draw fertilizer runoff and other pollutants out of the water, locking them safely away in meadow soil. Scientists have estimated that an acre of seagrass provides more than $11,000 worth of filtering every year….
In one survey, they collected seawater and put it in petri dishes to see if colonies of disease-causing bacteria known as Enterococcus grew from the samples. Levels of the bacteria in water from seagrass meadows, they found, were a third of the levels in water from other sites. In a second search, the scientists grabbed fragments of DNA floating in seawater. By examining the sequences, they identified 18 kinds of disease-causing bacteria. Water from the seagrass meadows had only half the level of this DNA, compared with water collected at other sites. The scientists next turned their attention to coral reefs around the islands. Reefs next to seagrass meadows, they found, were half as diseased as those without meadows.
…Seagrass meadows can store enormous amounts of carbon. Their soils don’t decompose because they have very little oxygen in them. As a result, seagrass meadow soil around the world has accumulated an estimated nine billion tons of carbon.
As seagrass meadows disappear, that carbon is being released back into the ocean. Some of it may make its way into the atmosphere as heat-trapping carbon dioxide. As dire as the situation has become, there is cause for hope. In recent years, Dr. Orth and his colleagues have successfully restored seagrass meadows off the coast of Virginia. “Now we have 6,200 acres of seagrass,” he said, “where in 1997 there wasn’t a single blade of grass.