On a warm May morning, a group of third-graders from Pensacola Beach Elementary huddled around vats of tangled seaweed, pulling apart clumps of amber-colored algae to reveal tiny crabs and other creatures hiding inside. Their teacher, Joy McLaurin, crouched among them, barefoot in the sand, shouting the day's science lesson over the surf.
She was interrupted mid-sentence by a rogue wave that barreled in, leaving the whole group soaking wet. The students laughed and shrieked with delight.
“You just learned the most important thing about the ocean,” McLaurin told them. “Never turn your back to it.”
For the students, the floating seaweed known as sargassum was a source of fascination. Elsewhere — across the Gulf Coast and Caribbean — it’s a growing source of dread. Massive mats of the algae are washing ashore in record-breaking quantities, rotting in the sun, destroying fishing gear, and driving away tourists.
And this year’s bloom? It’s among the worst ever. According to the University of South Florida, sargassum levels in April reached historic highs in the eastern Caribbean — more than double any previous April on record. And more is on the way.
For more than a decade, news story after news story has pointed to nutrient-rich runoff from major rivers like the Amazon and Mississippi as the most likely cause. That theory held intuitive appeal: fertilizer and other pollution flow downstream, feed the algae, and fuel its explosive growth. But new research from an international team of scientists has blown that tidy narrative out of the water.
“It’s very easy to make a conceptual connection between deforestation in the Amazon and nutrients in the river,” said Frank Muller-Karger, an oceanographer at the University of South Florida and co-author of the study. “It’s an easy connection — but it was published without evidence.”
Instead, Muller-Karger and his colleagues argue that a single, abnormal wind event in the winter of 2009–2010 may have kicked off a cycle that’s still playing out. Using 20 years of satellite imagery and ocean modeling, they discovered that unusually strong winds that winter pushed large amounts of sargassum southward from its traditional home in the North Atlantic into tropical waters.
Once there, it found “paradise,” as Muller-Karger put it — a warm, sun-drenched environment where upwelling currents bring deep-ocean nutrients to the surface. The algae thrived, bloomed, and began drifting westward into the Caribbean. In the years since, those blooms have become seasonal, self-sustaining phenomena.
“When these algae moved into the tropics, they could grow like crazy, basically all year round,” he said. “Whatever’s left the next year reforms by the wind, and the cycle continues.”
The 2009-2010 event appears to have been a one-off. But researchers say it marked a tipping point. The question is why. Muller-Karger says it may have been linked to a larger pattern of change.
“Climate change is full of surprises,” he noted. “You have these extreme events that are happening more often, so maybe that’s part of it.”
But the data aren’t conclusive. And that, Muller-Karger says, might be the lesson: Nature rarely follows a script — and neither should science. Sometimes, even our best theories get washed away.
Or, put another way: Never turn your back on the ocean.
