Trouble in paradise

By Tess De Klerk

Flying over the Caribbean Sea, we noticed large swathes of brown floating in the otherwise glistening waters. We kept staring out of our little window and the large brown patches just kept coming. Looking backwards from our high vantage point, looking forward as far as the eye could see, swathes of brown patches. Seafoam maybe? But the scale of it made that unlikely. We soon had our answer; sargassum seaweed – the scourge of the Caribbean

Since 2011, vast quantities of brown, bladdered, gas-filled seaweed have washed up on Caribbean coastlines, from the Lesser Antilles to Mexico’s Yucatán peninsula. Pre-2011, the cyclical algal blooms were largely beneficial while providing floating habitats for shrimp, whales, migratory birds and some 120 species of fish. Sea turtle hatchlings and juvenile fish would find shelter in the "golden floating rainforest" and nature was in balance. That was before the bloom exploded in size and volume; scientists using NASA satellite data recently clocked the floating seaweed belt at 5,549 miles long!

Now it entangles turtles, fish and dolphins too, fatally preventing them from surfacing for air.

The sargassum belt has been observed for as long as sailors have traversed the Atlantic, but in the past it has floated out at sea with small patches arriving at beaches, supporting the preservation of shorelines and sea banks. Now tons float up to shore, smothering seagrass meadows and coral reefs, choking beaches, harming human health and decimating tourist economies.

And it reeks! Sargassum itself isn't toxic but as it decomposes it releases hydrogen sulphide thus smells of rotten eggs and attracts swarms of insects. It turns crystal clear waters into a sulphurous brown mess. Swimmers can't get into the water, sometimes boats can't leave ports and locals tell of damage to household electronic equipment from the gases. Added to that, exposure to sulphide is blamed for neurological, respiratory, dermal and digestive symptoms. No wonder then, that Barbados declared the sargassum influx a national emergency in 2018.

BUT WHY THE EXPLOSION? Research gathered over the past decade has revealed three possible factors: Amazon discharge, Saharan dust clouds and warming temperatures.

Vast areas of heavily fertilised farmland and industrial-scale agriculture now exist where natural Amazonian forest used to be. Sewage and fertiliser run-off ends up in the Amazon River and flows out to sea, essentially over fertilising the Tropical Atlantic with excess nitrogen. Nutrients also pour into the Gulf of Mexico from the Mississippi River across which, climate change has caused dramatic increases in downpour and thus, runoff.

Saharan dust clouds that blow across the Atlantic Ocean is also believed to contribute to the explosion. The dust contains iron, nitrogen and phosphorus that fertilises plankton and algal blooms. These thick atmospheric dust plumes corresponded with a sargassum spike in 2015 and the worst incursion of sargassum in 2018.

A 30-year climate analysis by scientists with the National Oceanic and Atmospheric Administration revealed an overall warming trend of sea temperatures in the Caribean and Gulf of Mexico, with the most significant occurring over the past 15 years. Sargassum thrives in warmer water. Climate change also increases the upwelling of nutrients from deep ocean waters at the other end of the sargassum belt in West Africa.

Researchers are also exploring changes in ocean currents, which may be another contributing factor.

ENVIRONMENTAL ECONOMICS It was heartbreaking watching local people trying to stem the tide of mountains of seaweed with spades and pitchforks. The backbreaking work seemingly having no effect, their pristine beaches ruined. Our resort had heavy machinery working from dawn to dusk, some days achieving visible progress only to have even more sargassum pile up overnight – the work seemed pointless. We heard reports of seaweed six feet high, rotting in the Caribbean sun. The sulphurous scent of decay and unsightly mountains of seaweed is driving tourists away en masse from regions that depend on the industry. Some areas use offshore netting or floating bumpers to block or catch the seaweed which is then either diverted to 'sacrifice spots' or scooped up by expensive specialist boats and disposed of on land but as Rosa Rodríguez-Martínez, a researcher at the Universidad Nacional Autónoma de México tells us “None of the disposal sites, however, have been adequately prepared to avoid leachates (contaminated liquids) from reaching the aquifer,”

The cost of collecting and disposing of the rotting mass of algae off of Caribbean beaches peaked at US$120 million in 2018, and that number could rise considering the increasing amount of seaweed growing in the Atlantic. However, the tourism industry is not the only one affected by the large amounts of sargassum choking the environment. Fisheries from Florida to Mexico are concerned that the continued proliferation of algae in the Gulf will lead to a drop in fish stocks, potentially dealing a massive blow to the industry.

In 2019 the Mexican president enlisted the navy to help stop the tide of seaweed before it hit the coastline. Navy boats, manned by 300 personnel, now harvest sargassum from barriers installed at sea. As of May 2021, they’d collected more than 10,000 tons of it.

CAN THE PROBLEM BE SOLVED? It is important to note that the severity of the bloom ebbs and flows from year to year and area to area. One year a specific island might be hit particularly badly while the swathes might miss that same island entirely the following season but governments are expecting algal blooms to be as frequent as hurricanes – the new normal. Scientists and engineers have developed software and monitoring systems to predict where sargassum will make landfall, with varying degrees of success.

Communities have innovated ways of using it ranging from soap-making to biofuel and fertiliser. Some Mexican entrepreneurs are compressing the seaweed into bricks, used for construction but these small scale operations will hardly put a dent into the yearly deluge of pelagic seaweed.

In the long term, lasting solutions will come only through addressing climate change and the nitrogen footprint left by human activities.