Sargassum beginning to wash ashore on Riverside Conservancy’s newly installed living shoreline.
BY LISA D. MICKEY
It’s been called “the blob” and its arrival has elicited plenty of hand-wringing as shoreline deposits of the Great Atlantic Sargassum Belt have landed on beaches from Florida to the Caribbean.
A rootless, leafy, floating algae that typically forms an expansive raft of seaweed in the middle of the Atlantic Ocean’s Sargasso Sea, sargassum has dominated summer environmental headlines this year.
Why? Because the sargassum patch heading this way measures around 5,500 miles long and 300 miles wide. According to one National Public Radio (NPR) report, that’s “more than double the width of the contiguous U.S.”
Scientists speculate Atlantic beaches could experience the largest deposits of sargassum ever recorded from this seaweed patch weighing over an estimated 10 million tons. And as it moves west, the sargassum takes along with it whatever is in the ocean – including plastics, debris and high amounts of chemicals accumulating in ocean waters.
Once it reaches shore, all of that organic material piles up on beaches on the high-tide line known as beach wrack. The decaying seaweed produces both an unpleasant smell and a physical impediment for popular tourist sites.
Its massive accumulations on beaches also create an obstacle course for nesting sea turtles. And the swept-up collection of oceanic items in the beach-stranded sargassum also can deposit danger for beachgoers navigating across or through the thick clumps of gnarly vegetation.
“It is truly acting like a big broom mop out there in the equatorial gyres that can make the piles of sargassum dangerous to walk over,” said Dr. Wendy Anderson, a Stetson University professor and head of Stetson’s environmental science and studies department.
“After Hurricane Irma [in 2022], I found hypodermic needles, boards with rusty nails and other sharp, dangerous objects embedded in the Sargassum piles,” she added.
Sargassum is a natural occurrence that occupies a two-million-square-nautical-mile area in the middle of the North Atlantic. That sanctuary for marine life provides habitat and food for a cornucopia of animals, including sea turtles, which spend their early years living in the protection of the vegetative raft.
The Sargasso Sea lies off the west coast of Florida. Photo by Lopez Miranda et al. (CC BY 4.0).
The sargassum raft is surrounded by the Gulf Stream on the west, the North Atlantic Current on the north, the Canary Current on the east and the North Equatorial Current to the south. The ocean’s gyres swirl around the sargassum and largely contain the area, which is home to some species that only live in the unique biodiversity found there.
What is different, however, is that in recent years, much larger amounts of sargassum have deposited on Atlantic beaches from April to October -- largely during the months of June and July. This year’s sargassum deposit already is the largest ever recorded.
Scientists have puzzled over why the so-called “monster blooms” have started showing up on beaches -- sometimes dumping feet of brown, rotting seaweed on some beaches in Mexico and the Caribbean, requiring heavy equipment to clear resort areas and sea-turtle nesting sites.
Florida Atlantic University’s Brian Lapointe, who has studied sargassum for more than four decades, points to human influence for affecting oceanic nitrogen levels.
The density of sargassum in the ocean has been increasing over time.
“It’s almost like sargassum is a barometer for how global nitrogen levels are changing,” he said in a March NPR interview this year. “We’re using more fertilizer, burning biomass, cutting down forests and increasing wastewater from cities, all of which sends ammonium, nitrate and phosphate down major river systems.”
And those river systems, including the Mississippi, Amazon and Congo, connect to the oceans – which ultimately impacts Florida’s 1,350 miles of shoreline.
While Anderson’s studies at Stetson have looked more at impacts of beach plants and animals once sargassum has reached shore, rather than addressing the cause of the sargassum explosion, she agrees that nitrogen from the deforested Amazon, as well as atmospheric nitrogen dioxide, are key factors in the change.
She also believes that Saharan dust is a contributing factor.
“A lot of phosphorus blows off in that dust and settles out over the equatorial Atlantic where sargassum accumulates in small gyres,” said Anderson, whose Stetson environmental science students have served internships at Riverside Conservancy. “More Saharan dust is coming from expanding desertification and climate change.”
Dr. Stephen P. Leatherman agrees that Saharan dust clouds blown across the Atlantic contribute to accumulations of iron, nitrogen and phosphorus in the ocean’s sargassum beds. In a story he penned for Maritime Executive, the coastal geoscientist from Florida International University pointed to “dust storms in Saharan Africa” and “biomass burning in central and southern Africa” as human activities affecting the Sargasso Sea.
“As [the dust clouds] blow across the Atlantic, they help fertilize seaweed,” he said.
Some have suggested that the massive piles of sargassum could be used as organic fertilizer once cleaned of saltwater residue and dried, but Dr. Lapointe’s research has found that sargassum deposits “contain heavy metals, including arsenic,” which could pose risks for water tables.
In addition to the undesirable presence of such large amounts of sargassum comes the concern over how it could potentially choke out fragile coral reefs and important fisheries or change the pH in waters surrounding these sites.
As for sargassum entering the Indian River Lagoon in massive amounts, Anderson acknowledged that some sargassum will find its way into the estuary, but she doubts the tide will bring in enough of the seaweed for a negative impact.
“We could see some impacts from nutrient loading or hypoxia as it starts to decompose in the water,” said Anderson, who also serves as chair of Volusia County’s Soil & Water Conservation District Board of Supervisors. “[Sargassum] could settle down on top of the remaining and recovering seagrass beds and, like local algae, block sunlight.”
A piece of ocean plastic embedded within sargassum- a common occurrence in the newly washed up vegetation.
Anderson is most concerned about the amount of plastic embedded in sargassum that is washing onto shorelines. She noted that NASA predicts approximately 13 million tons of fresh sargassum will land on Florida and Caribbean beaches this year equaling between 2.5 to 3 million tons of dry material.
“The amount of plastic in that amount of dry material could be anywhere from 97,000 tons to more than 490,000 tons of plastic coming onto beaches,” Anderson said. “It’s good to get that plastic out of the ocean, but then what do we do with it when it returns to us embedded in the sargassum?”
Sargassum itself is not dangerous. It collects on coastal wrack lines with tides and provides a food source for shorebirds and ghost crabs. It also can dry and wash up against dunes, helping to collect sand, as well as to serve as compost for existing dune plants.
“The county budget for beach management is already strapped and removing [sargassum] is very expensive,” Anderson added. “Raking it up closer to the base of the dunes helps ‘clean the beach,’ while still leaving the material in a place where it can contribute to dune regeneration and support dune vegetation expansion.”
No doubt, beach goers this summer may have to navigate unusually large piles of sargassum, and sea turtles using beaches to nest will be challenged more than ever.
But looking ahead, Anderson does not see a change in the amount of sargassum that is predicted this year for Florida’s shorelines, the Caribbean islands and Mexico’s Yucatan peninsula.
“Nothing is going to stop it from coming ashore,” she said. “It is a fact of life for nearly all Florida beaches this year and into the foreseeable future.”