How to Harness Mega Seaweed Blobs For a More Sustainable Future

On Oct. 7, 1492, Christopher Columbus, aboard his ship the Santa María, had been at a complete standstill for 21 days, trapped in a very strange sea which he would later name the Sargasso Sea—sargazo in Spanish meaning “gulfweed.” Today, the Sargasso Sea—an elliptical expanse in the southwestern Atlantic at the center of which lies Bermuda—is six times the size of France, and is the only sea in the world with no shoreline. There was great anxiety among Columbus’s sailors as their already heavily rationed food supplies dwindled the longer they remained stuck. Not the slightest wind, not the slightest wave, only this tangle of seaweed as far as the eye could see—it felt as though the Santa María was destined to stay bogged down in the golden mass forever. But finally, a light breeze came and helped bush them through towards the shores of the Bahamas.
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As far back as 2,000 years ago, people were warned of the impenetrable Sargasso Sea. What caused such a mass of seaweed likely remained a mystery to Columbus. But today we have a better picture of what’s causing this phenomenon. The incredible accumulation of algae over millions of square miles is linked to a vortex created by the convergence of three great marine currents of the Atlantic—this clockwise circulation, generated as the ocean currents collide with one another, is known as the North Atlantic gyre. That vortex, and an excess of agricultural nutrients and chemicals that leak into the sea, is to blame. The resulting massive blobs of sargassum (a type of brown seaweed, also known as “golden tides”) are a growing challenge—as Florida is right now experiencing—but this seaweed also presents a multitude of untapped opportunities.

The first golden tides noticed in the U.S. were reported off the coasts of Texas and Florida in the 1980s. And since 2011, the proliferation of sargassum in the Caribbean has accelerated exponentially, multiplying its biomass tenfold in the space of a few years. The Great Atlantic Sargassum Belt now covers an area from Central America to the coast of West Africa. From Texas to Abidjan, these huge rafts form a strip of nearly 5,600 miles.

Read more: The Ocean Farmers Trying to Save the World With Seaweed

In the open sea, sargassum contributes to biodiversity by providing a refuge for turtles, crabs, and fish. But when their proliferation takes them near the coasts at the bottom of the Gulf of Mexico, they prevent light from penetrating which causes the corals and seagrasses to die. Once dead, the coral and seagrasses decompose and absorb all the oxygen, creating deserted areas on the shoreline to the detriment of fish, crustaceans, and turtles.

On land, however, they cover the shores for several miles in heaps over three feet thick, releasing a stench similar to rotten eggs as they decompose. The hydrogen sulfide they emit causes eye irritation, nausea, sore throat or ears, or itchy skin. This phenomenon destroys all tourist activities in disadvantaged areas where this income is essential to the population. The seaweed also clogs the propellers of fishing boats, preventing fishermen from working.

These mountains of seaweed are not exclusive to the Sargasso Sea. Today, much of the seaweed originates from a more southerly region, opposite Brazil, at the mouth of the Amazon. The banks of the world’s largest river have been suffering for years from the ravages of intensive agriculture and deforestation, and are spitting out an incalculable amount of nitrogen, phosphorus, and other waste into the ocean. Exhausted and leached soils regurgitate hundreds of thousands of gallons of pollutants and wastewater and act on the seaweed like oil thrown onto a fire: the seaweed proliferates and accumulates by millions of tons.

In 2011, there were 10 million metric tons of sargassum, in 2018, this figure reached 20 million metric tons. The problem with the sargassum is they’re incredibly difficult to eradicate, especially as their routes through the sea are almost impossible to predict. Studies are underway into offshore booms or boats specifically built to harvest them alive offshore, but the difficulty in predicting the location of the seaweed and the dates of its proliferation makes it complicated to implement these innovations. There are also some proposals to develop a means of sinking the seaweed in the open sea in order to sequester the carbon from its biomass in the marine sediments for thousands of years to come.

Read more: How Seaweed Helps Cows Become Better Climate Citizens

Rather than get rid of the seaweed, though, some people hope to transform it into something more useful. The most profitable potential at present seems to be in its alginate, which can be processed into biomaterials. Local investors in places such as Mexico, the Dominican Republic, and France are demonstrating a growing interest in using sargassum in biodegradable packaging. Other entrepreneurs are starting to manufacture building bricks using this sargassum. In 2018, a Mexican company built a house in two weeks from sargassum harvested on the coast of Puerto Morelos. It was dried and mixed with wet raw earth to form bricks which then hardened in the sun. According to studies by scientists from the National Autonomous University of Mexico (UNAM), a house made from these bricks can withstand earthquakes and strong winds. The bricks obtained by incorporating this brown seaweed provide much more resilience than traditional ones.

These solutions aren’t without their challenges. Industrial processing plants enabling these applications would be a possibility, but working out where to put them is complex given the imprecise location of the algal bloom from year to year. And the stakes are high. If no solution is found, then the very sargassum that struck terror into Columbus’s sailors could destroy the coastal resources—both biological and economic—of Central America and even Africa in the years to come. Unfortunately, there is no indication right now that the countries bordering the Amazon River are committed to taking action to limit deforestation, pollution, and the influx of nutrients and minerals into the ocean. After all, we must remember that sargassum is not the cause of our problems—it is a symptom.

Seaweed is too often perceived as a risk. On the contrary, it represents an opportunity. Its bad reputation is linked to the economic and ecological damage caused throughout the world by tides of seaweed that we’ve been unable to control or fully understand. So we must ask ourselves: What keys to progress might be hidden in seaweed and in our capacity to rediscover the ocean today?

The Seaweed Revolution by Vincent Doumeizel, translated by Charlotte Coombe, published by Hero in Hardback and ebook. Published in the U.K. on April 25, 2023 and in the U.S. on Sept. 5 2023.