An invasion is slowly advancing toward Florida’s shores: a massive island of seaweed. Weighing over six tons, it’s the latest in a series of algae blooms to plague Florida. While mats of this smelly brown algae have blanketed the tropical shores of the Caribbean before, this year may be the biggest bloom yet—spanning over 5,000 miles. Once confined to its namesake Sargasso Sea in the central Atlantic, a brown carpet now extends across the ocean. As we brace ourselves for the stacks of seaweed, the real culprit may be as slippery to pin down as the stuff itself.

Brown algae, or sargassum mats, are naturally occurring events, but since 2011, they’ve been popping up in the central Atlantic and Caribbean in much higher frequencies. Linked to a web of widespread phenomena, they impact tourism to human health. An important question remains are these brown, noxious beaches the new normal, a result of our heavy footprint on the planet? Or can we prevent them?

Sargassum blooms, veritable stacks of seaweed
A brown carpet of sargassum in Belize in gory detail

Seaweed by the Seashore

For starters, small mats of sargassum can be beneficial, providing food and protection for sea turtles, fish, crabs, and birds. They’re also important nursery areas for commercially fished species like mahi mahi, amberjacks, and jacks, while also helping to control beach erosion when washed ashore. The problem is when brown algae grows out of control. Large blooms can block sunlight, killing valuable seagrasses below. When the algae die and decompose, they can smother corals and deplete oxygen in the water, causing fish kills. Finally, they deter sea turtles from using critical nesting habitat, and hinder hatchlings as they attempt to swim offshore.

Sargassum Setbacks

With a smell of rotten eggs that can cause respiratory problems, it’s no wonder these slimy stacks of seaweed scare off tourists. When large algal blooms afflicted the Caribbean in 2018 and 2019, hotel occupancy dropped. For instance, in areas affected by sargassum blooms in 2018, Barbadian hotels saw their occupancy decline, while those in areas unmarred by seaweed enjoyed increased occupancy. Tourism in Caribbean islands can generate over $60 billion, making up a third to half of many countries’ GDP. Similarly, in Florida, tourism is one of the largest industries. It regularly contributes $80 to over $95 billion to the state’s GDP and supports millions of jobs.

To add insult to injury, the clean-up of sargassum is also expensive. In 2018, the Caribbean-wide clean-up cost over $120 million. And how to deal with the copious amounts of seaweed is problematic. Since it contains arsenic and other heavy metals, it’s unsuitable for eating or fertilizer. Yet leaving it alone can clog desalination and power plants, and damage fishing boats, equipment, and gear.

Sargassum blooms, veritable stacks of seaweed
More stinky sargassum, this time in Puerto Rico

Sources of the Stacks of Seaweed

Tackling the source of algal blooms is equally intractable. Like baking a loaf of bread, multiple ingredients are needed for an algal bloom. First, a seed population, or small amount of algae, is necessary for a bloom to take off. Then like sprinkling in some yeast, nutrient runoffs fuel algal blooms. Upwellings of nutrient-rich water in the eastern Atlantic contribute to a bloom’s growth, while polluted Amazon river discharges are another potential driver. Unfortunately, deforestation and fertilizer use in Brazil have both increased over time, and not surprisingly, so have levels of nitrogen in the waters east of Brazil. The U.S. is not off the hook either, since discharges from the Mississippi could be another contributing factor. On the other hand, higher temperatures on the ocean’s surface and lower salinity levels can suppress algal growth.

A Panamanian beach  unmarred by stacks of seaweek
Ahhh… a Caribbean beach unmarred by seaweed

Seaweed Solutions

What can we do to fend off the pending seaweed onslaught? Despite the hazards, entrepreneurs are taking a stab at the problem by developing products from the algae like fertilizers, particleboard, animal feed, compost, and charcoal. The Food and Agriculture Organization is also promoting ways to use the seaweed, for instance, in bricks, shoes, soap, and paper.

Another option is addressing the fuel behind algal blooms. A problem that’s only risen its slimy head in the last 10 years is clearly rooted in human activity. Cleaning up major rivers from the Mississippi to the Orinoco would help mitigate the blooms. While this would require major efforts, it may be the most permanent solution. If not, we may face additional sargassum-filled years, along with their hefty clean-up fees and damage to local industries.

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  1. Pingback:Stockpiles of Seaweed | Environmental conservat...

  2. Thanks for another great article! I have noticed an increase in seaweed along the beaches of Northern California over the past decade or so, but I didn’t understand the myriad of reasons behind this shift. I’m impressed by the solutions people are exploring, such as using seaweed to make particleboard, animal feed and compost, but it is disheartening that this change in sargassum is yet another ecological shift caused by human behavior.

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