Florida Algae Blob | The Great Atlantic Sargassum Belt, a 5,000-mile algal bloom visible from space, is now reaching the beaches of Florida

A 5,000-mile belt of algae lurking in the Atlantic Ocean has already begun washing up on Florida beaches.

The Great Atlantic Sargassum Belt — as the biomass is called that stretches from West Africa to the Gulf of Mexico — contains scattered patches of algae on the open sea rather than a coherent clump of sargassum. It’s not a new event, but satellite images taken in February showed an earlier onset than usual for such a large open-ocean accumulation.

University of South Florida researchers It was recently estimated that the algal bloom weighed 13 million tons and was still growing.

The European Space Agency said the bloom is visible from space and is likely the largest algal bloom ever recorded.

Once it washes ashore, sargassum is a nuisance – a thick, brown alga that blankets beaches, releasing a pungent odor as it decays and entangling people and animals who enter it. For hotels and resorts, beach clearance can result in 24/7 operations.

Here’s a look at this year’s sargassum algal bloom:

WHAT IS SARGASSUM?

A leafy brown alga adorned with what appear to be berries. The algae float in the open ocean and, unlike other algae, multiply on the water surface, supported by air-filled structures that give it buoyancy.

Sargassum originates in a vast stretch of the Atlantic Ocean called the Sargasso Sea, which lies well off the southeastern United States. The Sargasso has no land borders; Instead, four dominant ocean currents form its boundaries.

The matted brown algae stretches for miles across the ocean and provides breeding, food and habitat for fish, sea turtles and seabirds, according to the National Oceanic and Atmospheric Administration.

“It’s a dynamic, ever-changing set of parts of this great mass,” said Rick Lumpkin, director of NOAA’s Physical Oceanography Division. “It’s not a big continuous blob that flies straight to South Florida.”

WHY IS THIS A PROBLEM?

Sargassum accumulates on beaches, where it quickly decomposes under the hot sun, releasing gases that smell like rotten eggs.

In recent years, Sargassum has carpeted the beaches of some Caribbean islands and Mexico’s Yucatán Peninsula during the spring and summer months. Beach resorts and towns and hotels are struggling to keep up with the massive amounts of seaweed washing ashore.

WHAT IS THIS YEAR?

Some sargassum has already reached beaches in Key West, said Chuanmin Hu, a professor of oceanography at the University of South Florida. But most of it will arrive in the summer, Hu said.

“What’s unusual this year compared to previous years is that it started early,” Hu said. Normally, the algae bloom in spring and summer, but “this winter we already have a lot.”

South Florida, the Caribbean and the Yucatán Peninsula typically see accumulations of sargassum during the summer months and could expect the same this year, Hu said.

IS SO MUCH SARGASSUM UNUSUAL?

It’s a lot, but it was worse.

Scientists estimate that there are more than 10 million tons of sargassum in the belt this year. Lumpkin called it “one of the strongest years, but not the strongest” since scientists began closely monitoring the biomass using satellite imagery in 2011.

He said there were more in 2018. The years 2019 and 2021 also saw a lot of sargassum, he said.

WHAT CAUSES IT?

Scientists aren’t entirely sure, partly because it wasn’t closely monitored until 2011.

“We know that to get a lot of seaweed you need nutrients and you need sunlight. Of course there will be more sunlight as you get closer to the equator,” said Mike Parsons, a professor of marine sciences at Florida Gulf Coast University.

Parsons and other experts say agricultural runoff seeping into the Amazon and Orinoco rivers and eventually the ocean could explain the belt’s increased growth on the west side. Parsons said warming water likely helps the algae grow faster. Changes in wind patterns, ocean currents, rainfall and drought can also affect blooms.

“It may be that some years the entire belt is fed more than others by dust containing iron and other nutrients from the Sahara,” NOAA’s Lumpkin said.

It is unclear whether climate change is playing a role. Hu said extreme weather, which is becoming more common due to climate change — strong wind events, storms, more precipitation — could be contributing.

IS SARGASSUM HARMFUL TO HUMAN HEALTH?

It may be. As sargassum decomposes, it releases ammonia and hydrogen sulfide, which are responsible for the rotten-egg stench. Brief exposure isn’t enough to make people sick, but prolonged exposure — especially for people with respiratory problems — can be dangerous, scientists say.

Hu said this could be a problem for hotel workers and others who may spend hours cleaning the decaying sargassum off beaches.

Rotting on the beach, Sargassum can become a problem. It can damage coastal ecosystems and also supports the growth of fecal bacteria.

The Associated Press contributed to this report.