Sargassum en masse

You’ve probably heard it in the media for weeks now: a giant kelp mass about 5,000 miles wide is heading toward Florida, where it will engulf beaches with tons of nasty, decomposing algae, all the while releasing a noxious gas.

Inevitably, stories about this vast body of seaweed tend to refer to it as a stain, stirring up images of some 1950s B-movie monster coming to devour the Sunshine State, beaches, tourists, retirees and all. In fact, the so-called spot, although large, is well known to scientists and has been carefully studied for more than a decade. And it won’t just affect Florida. Here’s what we know about it.

It’s not a spot, it’s a bloom

A 2018 image of the belt, which is large enough to be seen from space. (Credit: NASA/Earth Observatory)

First, let’s call the stain what it is: an algal bloom. In this case, it is made from a type of brown algae, an algae known as sargassum.

This particular sargassum conglomerate even has an official name: The Great Atlantic Sargasso Belt, stretching from Africa to the Gulf of Mexico. Although it is believed to be the largest algal bloom on the planet, it is not one giant, continuous bloom, but several scattered across the Atlantic.

Read more: How did 5,500 miles of seaweed spread across the Atlantic?

What is Sargassum?

Sargassum itself has been floating in the ocean for a long time, about 30 million years. Unlike other types of seaweed that can attach to the seabed, sargassum drifts wherever the wind and tide take it, and is held to the water’s surface by a series of gas-filled pods.

Sargassum is too unique in that it is holopelagic, meaning it spends its entire life cycle in the open sea, rather than reproducing or originating from the ocean floor. Despite its ability to float, sargassum can be quite heavy – the current girdle is estimated to weigh 6 to 10 million tons.

The origin of Sargassum seaweed

(Credit: Public Domain/Wikimedia Commons)

Sailors have known about sargassum for hundreds of years – Christopher Columbus discovered it in the 15th century during his travels (or at least he was the first to document it in his journals). The word is derived from a Portuguese term for a similar-looking plant. Although sargassum species can be found in almost every ocean on the planet (except the Arctic Ocean – too cold), the seaweed usually originates from Sargasso Seaa large area of ​​the Atlantic Ocean whose boundaries are defined by ocean currents rather than by any land boundaries.

In the days of wooden sailing ships, this sea was particularly dangerous. Columbus, who is also credited with discovering the Sargasso Sea, noted concerns that massive clumps of floating kelp could trap a ship or hide dangerous shoals and reefs. Although it is possible for filamentous algae to foul a ship’s rudder, generally harmless sargassum mats pose little threat to a large ship.

The real danger to sailors was part of the Sargasso Sea, which included the infamous sea depression, an area that is feared because there is almost no wind. A becalmed sailing vessel can remain at sea for weeks or months, leaving a stranded crew with dwindling supplies of food and water. But you can’t blame seaweed for that.

Sargassum isn’t always bad

Sargassum serves as a habitat for about 70 different species, including crabs. (Credit: Jaimie Tuchman/Shutterstock)

Sargassum provides a unique ecosystem for a variety of sea creatures, according to the National Oceanic and Atmospheric Administration. Baby sea turtles love things and use the large mats as a species floating nursery. About 70 other species, including species of shrimp, crab, fish and even birds, have adapted specifically to the floating islands of sargassum as a habitat.

Like all seaweeds, sargassum is also excellent at sequestering carbon dioxide and producing oxygen through photosynthesis. This is all well and good for the environment. Unfortunately, other aspects of the environment contribute to the massive growth of seaweed, creating new problems.

Why is Sargassum a problem now?

(Credit: StephanKogelman/Shutterstock)

Thanks to climate change, even partially increased global temperatures translate into warmer water, accelerating algae growth. Meanwhile, changing ocean currents are influencing how far and wide the sargassum belt will spread. Since 2011, scientists have been watching the growth of the belt, which is large enough to be seen from space.

This isn’t even the first time stories about a “giant algae patch” have made their way into the news cycle. A few years ago, several stores, incl Find outbegan featuring news of the expanding belt, which is up to 5,500 miles wide, clogging Caribbean beaches and taking a serious hit to the tourism revenue of many resorts.

Read more: Stinky seaweed crosses the Atlantic Ocean in huge groups

The same will happen again this summer. Sargassum is now reported on beaches in the Florida Keys and will continue to wash ashore throughout the Gulf of Mexico.

What does this mean for people? Well, if you live in or plan to visit an area within the buoyancy belt, you may see a lot of sargassum landing on beaches at a depth of several feet. It would be extremely inconvenient to walk through it, and you should not try: among other reasons, you might be stung by the very small sea creatures that still inhabit the kelp.

Such huge amounts of sargassum can cause other problems as giant mats of seaweed have the potential to absorb all the oxygen from large areas of water, creating dead zones where other marine life cannot live. And once huge piles of sargassum begin to accumulate on the beach, everything begins to fall apart.

You can not write sargassum without gas and this seaweed is sure to deliver it when it reaches land. Decomposing sargassum releases ammonia and hydrogen sulfide, which, in addition to having an extremely unpleasant odor, can pose a health risk in concentrated amounts. At the very least, rotting algae can cause a lot of irritation to your eyes, nose, and throat—another reason to avoid getting near it.

Sargassum Solutions

(Credit: Kamira/Shutterstock)

Resorts from Florida to the Caribbean have already spent millions of dollars over the past few years deploying staff and equipment to remove stinking piles of sargassum from once-pristine beaches.

But to really solve the problems posed by such a huge amount of seaweed, what really needs to happen is a sustained effort not only to combat climate change, but also to reduce the amount of nutrients flowing into the ocean from places like Amazon River.

Nitrogen- and phosphorus-rich runoff from agricultural and other industries is believed to be a major factor in the enormous growth of sargassum. Until this can be corrected or reduced, you can expect future stories of the Great Atlantic Sargasso Belt when it may be even larger than it is today.

Read more: Algal blooms may have threatened these ancient cities

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