(NEXSTAR) – For the past few months, scientists have been sounding the alarm about a 5,000-mile long belt of seaweed that was threatening to wreak havoc on Florida and Caribbean beaches. The bloom of sargassum, a type of seaweed that smells like rotten eggs when it washes ashore and can cause breathing issues, reached record size in March – an estimated 13 million tons, University of South Florida (USF) researchers said.

But something unexpected has happened, the university team said last week: The mass shrank.

The quantity of seaweed found in the Great Atlantic Sargassum Belt (GASB), which stretches from the western coast of Africa into the Gulf of Mexico, shrank by 15% between April and May, according to the team of researchers that monitors sargassum’s growth and movement.

“Such a decrease for this time of the year never occurred in history since the first year (2011) of the GASB,” they wrote.

The biggest reductions in seaweed mass happened far from U.S. beaches, all the way in the eastern Atlantic Ocean. Closer to home, sargassum quantities actually went up in the western Atlantic and the Gulf.

What does this mean for the beaches already being inundated with seaweed? The future is murky for most places, the researchers admit – but there is some hope for Florida.

In the Gulf of Mexico, “Sargassum quantity is likely to decrease in June, which should be good news to the residents along the Florida Keys and east coast of Florida,” the USF researchers said.

Still, they expect the problematic seaweed to be present in “substantial” amounts through June before decreasing later in the summer.

Since 2011, the seaweed’s geographic area has massively expanded. 

In normal quantities, sargassum can actually contribute to a healthy ocean ecosystem. The problems start when it comes on land and starts to rot. As it decays, sargassum lets off hydrogen sulfide and smells like rotten eggs, explains the Florida Department of Health.

It can irritate people’s eyes, nose and throat, and trigger breathing issues for people with asthma.

The Department of Health recommends beachgoers avoid touching or swimming near the seaweed. The small creatures that live inside it, like jellyfish larvae, could sting or cause your skin to itch.

The department also suggests using gloves if you have to handle sargassum and closing windows if you live near the beach to avoid breathing issues and bad smells.