Environment | Martinique

The brown plague

The French island of Martinique is under attack from rotting Sargasso algae and the toxic gases it releases

An older man with white hair stands on the beach and looks at the water, in front of him the whole beach is covered with brown algae.

Thierry Lebrun in front of his house, on the beach polluted by Sargassum weed

From his terrace, Thierry Lebrun has a wonderful view of Cayol Bay, north of the small town of Le Robert on the east coast of Martinique. Only a stretch of grass, framed by palm trees, lies between his house and the beach but this April, Lebrun, an anaesthetist at the island's university hospital (CHUM), had to forgo a refreshing swim in the Atlantic, despite the tropical heat. “I used to swim in the sea every day after work,” recalls Lebrun, who has lived here since 1992. Now he can only enjoy this particular piece of paradise if he holds his nose. A stench akin to rotten eggs hangs in the air, and what used to be a bright, sandy beach now resembles a muddy marsh, sloshing with brown water.

Thierry Lebrun is one of the many residents of Le Robert who suffer the effects of beached Sargassum algae. The floating algae, also called gulfweed or brown algae, is rough and sticky to the touch, and grows in bush-like clumps. Sargassum algae was first reported in Europe by 15th century sailors and lent its name to the Sargasso Sea in the Atlantic Ocean.

However, the Sargassum inundating the coastlines of the Caribbean since 2011 does not appear to have originated there. Satellite images point to the waters between Brazil and the Gulf of Guinea as its place of origin although why it’s spreading quite so vigorously, and whether the increase in nutrients such as nitrogen and nitrates in the runoff from intensive agriculture in the Amazon plays a role, is still being investigated.

As it grows, the Sargassum forms a kind of algal carpet, sometimes measuring hundreds of kilometres in length and several metres thick. As long as it remains floating on the water’s surface, it’s harmless, even beneficial, as it provides both food and shelter for other marine organisms. But when the brown algae inundates bays and mangrove swamps and washes up on beaches, it turns deadly, choking coral and fish and stopping turtles from laying eggs.

Once stranded the algae starts to rot, releasing toxic gases such as ammonia (NH3) and hydrogen sulphide (H2S); quickly, the Sargassum morphs from marine habitat to health hazard and environmental fiasco. “It feels like your nose is blocked. The stench even gets into your clothes,” reports Jocelyne, who lives with her 97-year-old mother near the beach in Le Robert. “Here we’re lucky because there’s usually a breeze,” she says, sluicingher terrace with a mop. After emptying the bucket, she plugs the drain with a piece of cloth. “So the smell doesn't creep up through the pipes,” she explains.

“Further massive inundations of Sargassum algae are a constant fear for those directly affected” 

“You get used to the smell,” says Thierry Lebrun, who acts as a kind of regional whistle-blower regarding the health hazards of the algae. He lists his symptoms: “Sore throat, itchy eyes, frequent headaches, indigestion.” Hydrogen sulphide can be smelled even in tiny quantities; the odour threshold is 0.13 ppm (parts per million). From 500 ppm upwards, neurological symptoms ranging from loss of consciousness to coma can occur, in addition to breathing, blood pressure and heart problems. As yet, no deaths directly caused by the algae have been reported but this may only be because the available data refers to short periods of time.

To envisage the health effects of the beached Sargassum, one only has to look at the damage caused by the ammonia and hydrogen sulphide fumes to local houses: blackened bathroom ceilings, walls and fittings, electrical household appliances that oxidise and give up the ghost with worrying frequency. The algal blooms have economic consequences too, most obviously for fishermen but for the tourism industry too. In times of high algae inundation, holidaymakers dreaming of Martinique's picture-postcard beaches are heartily disappointed.

Initially, the algal blooms were seasonal and coincided with the holiday season, which lasts from December to April. In 2015 and 2018, a vast amount of brown algae washed up in the Antilles, covering all the bays on the Atlantic coast and bringing economic life to a standstill. Since then, less algae has washed up but more frequently, so that inundations occur almost year round.

Between November 2018 and April 2019, the Martinique Chamber of Commerce and Industry conducted a survey of more than 500 tourism businesses in nine particularly affected towns. The majority reported high losses in revenue (€1,862,000 in total) and property damage (around €330,000). “When there’s a lot of algae, tourists have to wade through sludge. I often cancel tours in advance without telling the customers that an algal bloom is the reason,” admits Henri Louis Roussel, who estimates the decrease in his income at 40 percent. He has a kayak rental business south of Le Robert and in 2020 was forced to close his business for four months because of the algae.

Not far from Roussel’s kayak rental is the four-star Plein Soleil hotel, which has been semi-successful in containing the effects of the algae by cleaning twice as often and as intensively as before. “The smell is not as bad here, but we have a lot of property damage,” reports co-director Marie Guinée.

The best way to fight the worst effects of the algae is to get rid of it before it rots. The city of Le Robert has been deploying algae barriers made of floats and nets in the water since 2014; six of the municipality’s 41 kilometres of coastline are currently protected. Boats pull the algae out of the water using suction and bring it ashore to dry. If the algae has already reached land, it should be removed and dried, but not all stretches of the coastline are accessible and as yet, there is no one officially designated area to dry the Sargassum.

Besides, no one really knows what to do with the seaweed afterwards. "It’s a constant battle,” explains Bruno Leconte, who is in charge of algae management for the city. Yet he remains optimistic: “Little by little we’re finding a more permanent solution.” Leconte estimates that collecting the algae has “cost at least six million euro since the beginning of the crisis”.

The fact that even this huge financial outlay is insufficient makes many islanders shake their heads. Further massive inundations of Sargassum algae are a constant fear for those directly affected, many of whom are still desperately waiting for the rotting algae which washed up months ago to finally be removed. 

Translated by Andreas Bredenfeld and Louise East