TAMPA, Fla. (WFLA) — By now you’ve probably seen the countless headlines about the giant Sargassum seaweed invasion headed for Florida. These Sargassum blooms have been booming over the last several years, and although science has not nailed down the exact reasons why there is one common denominator.

WFLA’s Chief Meteorologist and Climate Specialist Jeff Berardelli spoke to Dr. Brian Barnes, an expert on marine sciences from USF. Barnes says 2022 was the biggest bloom we’ve ever seen and this bloom is shaping up to be about the same size, if not bigger.

Besides the unusual suspects like red tide and blue-green algae, sargassum has recently become a yearly concern. Nowadays, these blooms extend 5,000 miles clear across the Atlantic from Africa to the Gulf of Mexico.

2023 Great Sargassum Belt (red = highest concentration)

“Before 2011 we never saw anything like this. In 2011 something happened whereby we started to be able to see it in mass using satellites and quantify it,” Barnes explained. Since then, Barnes says each year the blooms are getting bigger.

Sargassum are naturally occurring and in moderation, it’s a good thing because the seaweed supports abundant marine life. But over the past few years, the extreme outbreaks are inundating beaches in the Caribbean and South Florida, making for an eyesore at first, and then a smelly, toxic mix as it decays.

A worker pauses from removing sargassum seaweed from the shore of Playa del Carmen, Mexico, Wednesday, May 8, 2019. The problem affects almost all the islands and mainland beaches in the Caribbean. (AP Photo/Victor Ruiz)

Scientists are not exactly sure what triggered the 2011 event past a threshold. It was likely a confluence of environmental events. But one thing stands out in the research – an overabundance of nutrients.

“You’ve got the seed and then the fertilizer could be coming from areas like the watersheds in the Congo in West Africa, the Orinoco in the Amazon and then also the Mississippi River in North America,” explained Barnes.

Sediment and nutrient discharge from the Amazon (NASA)

“People that track this have looked at the nutrient concentrations coming out of those rivers and you see higher amounts of nutrients. That is the type of fuel that can sustain this type larger biomass event.”

A 2021 paper found that over the last 4 decades, Nitrogen concentrations in the Sargassum have increased by 35%, and phosphorus has decreased by 44%, resulting in a 111% increase in the Nitrogen to Phosphorus ratio, essentially throwing off the balance.

While this part seems clear, the contribution of climate change is not.

“We know that the waters are warming, is that having something to do with the increase in sargassum?,” asks Berardelli. “It’s not as straightforward as you think. Some algae are pretty much the warmer the better and they just thrive on super hot temps. Sargassum aren’t there,” explains Barnes.

So, if climate change is having an impact on Sargassum it’s likely more indirect. There’s some research to suggest changes in Atlantic Ocean currents and dust from Africa may be factors, both of which can be affected by a changing climate.

Dust plumes from the Sahara Desert of Africa

But there is good news for the Tampa Bay area. Sargassum is typically not a threat here. Barns says that’s because the Loop Current, which transports Sargassum north from the Caribbean into the Gulf of Mexico, typically remains far offshore of Tampa Bay.

The Loop Current moves north from the Caribbean into the Gulf of Mexico, loops around, and then moves back southeast into the Florida Straits and out into the Atlantic Ocean.

The Sargassum makes the loop offshore in the central Gulf, then heads back south in between the Florida Keys and Cuba, and eventually back out into the Atlantic Ocean by way of the Gulf Stream.

The take home is this: whether it’s sargassum, red tide, blue-green algae, oxygen dead zones or dying sea grass and manatees, it’s all related to the endless flow of nutrient pollution into our waters. Until we fix that, algae blooms will continue to boom.