The coast may be clear now, but sargassum is heading from the Caribbean to Florida shores, scientists warn


A report by Amy Bennett Williams for USA Today.

Though the Lee and Collier coastlines are looking pretty clear at the moment, scientists warn beach-clogging blooms of sargassum may appear in the not-so-distant future.

University of South Florida oceanography professor Chuanmin Hu’s monthly sargassum forecast predicts that vast drifts of the floating giant lifeform – scientists don’t include it in the plant kingdom – could reach the Florida Straits next month.

The satellite-based model shows the sargassum currently making its way from the eastern Caribbean to South Florida. Depending on winds and current, researchers estimate an early July arrival.

On a recent afternoon, though, only the occasional strand of sargassum tumbled in the Sanibel surf.

Small amounts are a familiar sight on South Florida beaches, but in 2018 record-breaking amounts washed up, carpeting the shoreline in springy brown tangles that become foul-smelling as they decompose.

Last summer, it messed up Naples beaches, creating smelly headaches for city workers, who had to gather it up and haul it off.

The USF forecast isn’t calling for a catastrophic level of the stuff, but it does anticipate an above-average year. “The current is very fast,” Hu told USA Today Network Florida earlier this week. “It has reached Jamaica. In June, it could be transported into the eastern Gulf of Mexico.”

The most recent USF forecast said the total amount of sargassum grew from 4.3 million metric tons in March to 5.8 miin April — a 35 percent increase and about the same amount as in April 2015.

Sargassum is a macroalgae, commonly known as seaweed, and not to be confused with seagrasses, said Sanibel-Captiva Foundation research scientist Rick Bartleson.

Sargassum, which forms huge offshore mats, shelters young sea creatures, including baby sea turtles. The Sanibel-Captiva Foundation’s Rae Ann Wessel calls it “a floating hotel and nursery to a myriad of other organisms. Small sea turtles swim near the seaweed looking for cover and an easy meal of the shrimp and crabs that live there.”

The loggerheads that nest on Southwest Florida beaches swim thousands of miles to the Sargasso Sea in the North Atlantic to spend about a decade feeding on jellyfish, snails, crabs and shrimps protected from predators in the sargassum. “It is breakfast, lunch, dinner and home to them,” Wessel says.

Buoyed by small, gas-filled beads, sargassum gets pushed around by ocean currents. When waves break apart, the pieces reproduce asexually. Some of it eventually washes onshore, where it can make a nuisance of itself, snarling boat props and fouling beaches. Too much of it keep newly hatched sea turtles from reaching the water.

The island of Bonaire is already reporting sargassum beachings with the Bonaire National Parks Foundation asking for volunteers to help clean beaches. The Yucatan Times had an article April 26 saying Cancun is bracing for sargassum mats to reach its beaches in late May or June.

“This is the time of year the blooms start coming into the Caribbean and they are heading this way,” Brian LaPointe, a researcher at Florida Atlantic University’s Harbor Branch Oceanographic Institute, told the Sun Sentinel. “A number of islands have been reporting inundations.”

The 2018 seaweed ambush bled into 2019 with sargassum stacked thigh high south of the Palm Beach Inlet into July, but it was mostly gone from South Florida after Hurricane Dorian’s disastrous crawl through the northern Bahamas in early September that year.

While hurricane-induced waves can wash sargassum from the beaches, Hu said it’s unclear what impact tropical cyclones ultimately have on the bloom mats in the ocean. Heavy winds could churn up nutrients from lower levels of the water column that feed the blooms. At the same time, a turbulent ocean could burst the plants’ air bladders, LaPointe said.

LaPointe and Hu co-authored a study published last year in Science magazine that found sargassum growth spurts occur in years when runoff from the Amazon River includes large amounts of fertilizer. The seaweed can also increase when upwelling in the eastern Atlantic brings cooler water and nutrients from the bottom of the ocean to the surface.

— USA Today Network Florida Contributed to this report.

A field guide to some Southwest Florida seaweed

Red drift This is a catch-all term for several varieties of fast-growing saltwater plants. Common in the region’s estuaries and bays, where it anchors itself to rocks, submerged logs or even large pieces of scrap metal, it can be red, brown or green. Broken-off pieces are often found washed up on the shore, sometimes in such great quantity that they clog and foul the beaches and discourage visitors.

Dead man’s fingers: Though a common sight on Southwest Florida shores, this rubbery manroalgae in the Codium genusoriginated in the coastal areas of Japan and has since has made its way around the world. Also called “green sea fingers” for its swollen, finger-shaped branches that float in the water, or hang down the sides of rocks when the tide is out. These “fingers” consist of plump, rounded branches that originate from a central fleshy mass.

Sargassum: A favorite with young beach-goers because of its pea-sized air bladders, which can be popped like bubble wrap, those tiny organs are what allow this saltwater plant to float offshore, sometimes forming huge drifting rafts. Those floating mats become life-giving islands to a variety of seabirds, more than 100 fish species, 145 invertebrates and five sea turtles. Once harvested for cattle feed, it’s now federally protected because it’s so ecologically valuable. That is, when it’s alive. Once it’s washed up on the beach, it’s legally fair game for the kids.

— The News-Press archives contributed to this report.

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