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Seagrasses Could Hold Secret to Averting Climate Change

Posidonia Oceanica, or Mediterranean seagrass, off the island of Naxos, Greece. Credit: Mark Burgess / CC BY-SA 3.0

Seagrasses, called by one researcher the Earth’s “forgotten ecosystem,” could hep us stave off further climate change if they are protected, as they ought to be all around the oceans and seas of the world.

As some of the oldest living organisms on the face of the earth — perhaps the oldest of all, some believe — this is the hypothesis of Emmett Duffy, the director of the Smithsonian’s Tennenbaum Marine Observatories Network who conducted research recently into the importance of these grasses in the ecosystem.

In a recent report in Smithsonian Magazine, he states that their ubiquitousness is deceiving: “They’re like the Serengeti grasslands of Africa — but hardly anybody knows about them.”

Often overlooked while the scientific community focuses on other sealife such as fish, shellfish and the great mammals of the oceans like whales, the humble seagrasses have survived for many millennia, perhaps even being the oldest living thing on the planet and serving an essential role in the health of our oceans and seas.

Seagrasses are some of the oldest living things on Earth

In the Mediterranean, scientists are now studying the common seagrass there, called Posidonia oceanica; they estimate that the largest grouping of grass — which are all clones of one another — is over nine miles. Its members have been sending out slow-growing rhizomes for at least tens of thousands of years.

Incredibly, this patch of grass may even be as old as 200,000 years, making it by far the oldest-known organism living on Earth.

Called Neptune grass, this is one of approximately 70 species of seagrasses that have spread over the eons across the shallower waters of the Earth, at a depth of less than ten feet, along the borders of every continent except Antarctica, and in seas worldwide.

Seaweed, which can be confused with seagrasses, are actually a form of algae, not true plants, and incredibly they did not form and evolve in the great waters of the Earth, but migrated there from land. Millions of years ago, as the largest dinosaurs the world has ever seen roamed the Earth, seagrasses moved from land and colonized the seas.

And since that time they have spread throughout every niche in this habitat. Unlike seaweed, seagrasses actually have true leaves, roots, rhizomes, veins — and even flowers. Incredibly, they even effect pollination in the sea, creating “buoyant seeds that can drift with the current before settling,” Smithsonian reports, with their leaves easily dealing with the adaptations needed to live under the salt water.

Seagrasses are “ecological engineers,” the researchers say, with their roots holding sediments in place and their leaves helping to keep silts from floating away, making the waters clearer.

Storm abatement, oxygenation of waters, shelter and fodder for sealife only some of benefits of seagrasses

Much like the mangrove forests that line tropical shores, seagrasses also of course keep storms from ravaging coastlines — even slowing water currents down. On a chemical level, as plants, they filter out polluting chemicals while they also give oxygen to the water, taking carbon dioxide down into the seafloor itself.

A U.N. report that was issued in 2020 estimates that seagrasses may be responsible for up to 18 percent of the ocean’s carbon sequestration — although they are over only 0.1 percent of the seabeds around the world.

Also of course, the swaying fronds of seagrasses are home to multitudes of sea creatures, forming vital habitat and shelter for them. The grasses also serve as fodder for turtles, sea horses, crustaceans, waterfowl and marine mammals.

Perhaps most incredibly of all, the vast swaths of seagrasses that line out shores are nurseries for no less than 20 percent of all the fish in the oceans and seas of the earth.

“Seagrasses are the forgotten ecosystem,” Ronald Jumeau, a United Nations representative from the Republic of Seychelles, states in the U.N. report. However, he says, they “are among the most productive natural habitats on land or sea.”

Some seagrasses up to 35 feet long

The colonization of the waters by seagrasses has led them to cover approximately 116,000 square miles of the seabed around the globe; although usually not more than a few feet or at most a meter long, some types of grasses are as much as 35 feet long, including the graceful Zostera caulescens, which has colonized the coasts of Japan.

Truly one of the most striking qualities of seagrass is that it makes sound. Carlos Duarte, a leading international seagrass expert at Saudi Arabia’s King Abdullah University of Science and Technology, describes that we can hear a “scintillating sound when you lie in seagrass meadows.”

This, he says, happens when oxygen bubbles produced by the seagrasses burst — which he likens to a sound “like little bells.” In a manifestation of the almost unfathomable intricacy of the natural world, Duarte believes that these tiny bell rings may be picked up by certain some sea animals that need the meadows of seagrass for vital habitat or even just temporary shelter.

He gives as an example, fish that have larvae which need to use the grass as a nursery, may use these tinkling sounds to guide them to just where they need to be.

Of course, like so much of the other living organisms in our natural world, seagrasses are also threatened, by the likes of runoff from commercial fertilizers, which fosters algae blooms which block out the sunlight needed by the grasses.

Scientists believe as much as seven percent of all the seagrasses of the world disappear each year, which is much like the level of decline seen in coral reefs and tropical rainforests as well.

Of course, the manatees, sea turtles and other animals that need the seagrasses for shelter and fodder are threatened in turn.

Powerful storms also of course wreak havoc, as they churn up waters especially along the shorelines, where the grasses tend to grow. An exceptionally severe hurricane in 1933 along the Eastern seaboard of the United States from North Carolina to Canada were almost completely destroyed all the seagrasses along the coast that hadn’t been killed off as the result of a slime mold disease.

Seagrass beds reestablished off East Coast of the US

But the resilience of the grasses was shown by its near complete recovery by the 1960’s, although some areas were still barren of the grasses they once were home to.

Robert Orth, a marine ecologist at the Virginia Institute of Marine Science, headed a team that determined to replant seagrasses where they had been eradicated, beginning their quest in 1999, when they planted eelgrass in the Atlantic.

After dispersing a total of 74.5 million eelgrass seeds into almost a square mile of seabed, his reseeding project has enjoyed tremendous success in the 21 years of its operation. Now with eelgrass covering almost 13 square miles of the ocean bottom, his is now seen by scientists as one of the most successful such efforts anywhere in the world.

Noting that sealife is using his seagrass beds for food and shelter once again, he tells Smithsonian “It’s a good-news story. If the plants aren’t challenged by water quality, they can spread naturally very quickly.”

Other areas in Florida, Europe and Australia have also experienced success in restoring seagrass beds, even by just utilizing passive restoration methods including reducing fertilizer runoff.

One of the most important tools yet in the effort to help seagrass thrive in our oceans and seas is the creation of a map of seagrass colonies globally, which will at the very least show scientists what kind of grass is growing where and what is most at risk.

Duffy, of the Smithsonian Institution, says “Getting an accurate global map of seagrass distribution is really important for understanding the fisheries that depend on them as well as their contributions to carbon storage.”

SeagrassSpotter app lets citizens do their part to help fragile ecosystem

He and his team are using footage obtained by drones to look at seagrasses along the North American Pacific Coast, where new outbreaks of the slime mold are now threatening  seagrass meadows.

As with so much of our world now, citizen scientists can also do their part; by using an app called SeagrassSpotter, they can report where they see seagrass beds in the ocean. Duarte, who lives near the Red Sea in Saudi Arabia, is even using radio signal-tagged marine animals to gather information.

“We are finding seagrass meadows by collaborating with sea turtles and tiger sharks,” he says.

Jonathan Lefcheck, a research scientist at the Smithsonian’s Environmental Research Center, is devoted to the effort to help seagrasses survive the depredations of humanity. “If we invest in seagrasses, they can help us in lowering the global concentration of carbon dioxide,” he explains, saying that this concept isn’t much different that that of realizing, as most people do now, that forests not only take C02 out of our atmosphere, they emit vital oxygen back into it.

He believes that seagrass meadows can work just as well as as a forest in taking out carbon dioxide and placing it down into the sediments, to stay there for decades or perhaps even centuries. He states hopefully, “I’m pitching seagrasses as an ally in climate change. They are an incredible ecosystem that continue to provide a wealth of benefits to humanity.”

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