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There's a Seaweed Blob Wider than America Coming to Clog Your Prop

It's hard to rattle a veteran boater -- they've seen it all before. Big water, bad weather, and boat trouble are just a few things things that cause the grey hair on a captain's head.

But sometimes, something so odd comes along that even captains tilt their heads.

There is a blob of seaweed wider than America headed for the East Coast. Move over white whales, giant squid, and assorted sea creatures, there is a new sea monster.

A massive raft of seaweed is headed across the Caribbean and towards the U.S. coast, seemingly with a beeline for the entire stretch between Key Largo and Fort Lauderdale. The seaweed is an algae species known as Sargassum. It grows in masses that remain afloat thanks to small air-filled sacs in their leaf structures. The floating masses are actually quite common, but 2023 will be different.

The blobs form between the Caribbean and West Africa in the Sargasso Sea (notice the name), at which point currents push them west into the East Coast of North America. This summer a unique combination of nutrient-rich water, steady currents, and bad luck have created an unusually large mass.

While some scientists are trying to downplay the potential for a big blob in 2023, this year's Sargassum bloom is already clogging coastlines along the Eastern Seaboard and the island chains to the southeast. Small arrivals have already been recorded on several Florida beaches. The current mass is expected to span more than 5000 miles (8000 kilometers) and stretches all the way from the coast of Africa to the Gulf of Mexico. Locations as far away as Mexico have been told to prepare for up to three feet of Sargassum on their beaches.

In an interview with Scientific American, Brian Lapointe, an oceanographer at Florida Atlantic University, said the phenomenon is here to stay: “2018 was the record year, and we’ve had several big years since. This is the new normal, and we’re going to have to adapt to it.”

Not only do the masses wreak havoc on both commercial and recreational boat traffic around the coast, once they reach the shore they put an enormous burden on local resources that have to collect and remove the rotting remains.

The 2023 mass has been dubbed the Great Atlantic Sargassum Belt, which is both apt and epic. According to Chuanmin Hu, an oceanographer at the University of South Florida in the Scientific American piece, the 2022 mass was the heaviest ever recorded in the Atlantic, accounting for over 22 million metric tons of seaweed. His team uses satellite from NASA and the National Oceanic and Atmospheric Administration (NOAA) to calculate their size. Hu is confident the 2023 mass will be the largest yet.

As the blob has gained steam through the month of March, Hu proffered: “This month there should be more. There’s no doubt. Even in the first two weeks, I have seen increased amounts.” The masses peak in June but arrivals can occur as late as October.

Now, that's not to say that Sargassum is entirely a bad thing. It may be a scourge to boaters, but it's a boon for the ocean. The bloom is essentially its own floating ecosystem, absorbing CO2 and nutrients while providing food and resources to marine wildlife. It's only once it reaches the shore and beings rotting that it becomes a nuisance.

Locations in Florida like Fort Lauderdale, and as far south as Key Largo, are already seeing Sargassum blooms wash up on shore. Not only does this block beaches and disrupt tourist and recreational traffic, the rotting weeds also release hydrogen sulfide gas, which has a pungent aroma like rotten eggs. Repeated exposure can also irritate the sinuses and eyes, causing headaches, nausea, and breathing issues.

Lapointe says the total size of 2023 Sargassum bloom can't be predicted yet. The warmer summer weather and the movement of the mass in conjunction with tides and currents will ultimately determine its final size.

“This is pretty early in the Sargassum season to see that much coming in, so I think that’s also fueling some of the concern about what’s to come,” Lapointe told Scientific American.

So what does this mean for boaters?

Generally speaking, it will require boaters to modify their trips and navigation routes in accordance with the location of the bloom(s). The Florida Department of Environmental Protection even has an Algal Bloom Dashboard where you can check the status and location of seaweed in your area. The University of South Florida's Optical Oceanic Laboratory also offers Sargassum Outlook Bulletins every month.

Boaters will also be at an increased risk of clogging their impeller or propeller. Trying to go through one of the blooms is nearly impossible. Make sure you have the proper propeller to match your boat and know how to maintain it. If you're a jet boater, you'd also be wise to weigh the pros and cons of going out in a Sargassum bloom.

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