What do we know about the huge mass of seaweed approaching the Caribbean?

21-03-23

A huge mass of seaweed originating in the Atlantic is heading towards Florida and other coasts in the Gulf of Mexico and the Caribbean, where it could litter beaches with foul-smelling and potentially deadly piles, and severely disrupt the region's tourism industry.

In the Atlantic, a type of seaweed known as sargassum has been accumulating rapidly since 2011, and scientists have been monitoring the phenomenon ever since. At more than five thousand nautical miles long, from the coast of Africa to the Gulf of Mexico, this year's mass of sargassum may be the longest ever recorded.

Dr Brian Lapointe, a researcher at Florida Atlantic University's Harbor Branch Oceanographic Center, predicts that the seaweed will be abundant on Florida's beaches by July, when the blob will continue to move westward into the Caribbean and the Gulf of Mexico this summer.

Throughout December and January, the sargassum bloom doubled in size, according to Lapointe. "It was bigger in January than it has ever been since this new sargassum growth region started in 2011," Lapointe told Rosemary Church.

"This is a completely new oceanographic phenomenon that is creating such a problem - a catastrophic problem - for tourism in the Caribbean region, where it is piling up on beaches up to 5 or 6 feet deep," Lapointe added.

He noted that in Barbados, local people were using "1,600 dump trucks a day to clean the beaches of this seaweed and make them suitable for tourists and beach recreation".

Although the terms "sargassum" and "sargassum nations" are sometimes used interchangeably, the two most common species of sargassum in the Atlantic are distinct. The algae have their advantages when drifting in the sea.

"This floating habitat provides food and protection for fish, mammals, seabirds, crabs and others," according to the Sargassum Information Hub website, which is a joint project of several research institutions. "It serves as critical habitat for endangered loggerhead sea turtles and a nursery ground for a variety of commercially important fish such as mahi mahi mahi, jack mackerel and amberjack.

Sargassum causes problems when it washes ashore, where it can form impassable mounds and release a gas that has been likened to rotten eggs. In a short time, it can go from helping to harming marine life.

It is produced in such large quantities that it absorbs oxygen from the water and creates what we call dead zones," explains Lapointe.

According to Lapointe, sargassum is equally harmful to people. Hydrogen sulphide, the gas given off by the decomposing algae, is poisonous and can cause breathing difficulties. "You have to be very careful when cleaning beaches," he warned.

Arsenic can be found in the flesh of seaweed, making it poisonous both when eaten and when used as fertiliser.

"If you're collecting this seaweed somewhere to use as fertiliser, you have to be very careful, especially if you're using it as food and fibre for human consumption," Lapointe told CNN.

The Sargasso Information Centre points to the millions of dollars needed to clean up the piles of algae that have washed up on beaches.

According to oceanographer Dr Gustavo Jorge Goni of NOAA's Atlantic Oceanographic and Meteorological Laboratory, algae growth varies from year to year depending on ecological factors, such as variations in nutrients, rainfall and wind conditions, as well as plant and crop growth on land.

Goni also noted that ocean currents can affect the annual growth and accumulation of sargassum. Algae can also feed on phosphorus and nitrogen in the ocean.

Lapointe took samples from the area where the sargassum originated and compared them with older samples from the 1980s; he found that the nitrogen level had increased by 45%. The exponential expansion of the bloom has led scientists to suspect a rebound.

The EPA reports that rivers can discharge phosphorus and nitrogen into the ocean from human activities such as agriculture and fossil fuel production.

According to Goni, researchers are studying possible solutions to reduce their impact on beaches, such as sinking the algae to the ocean floor or harvesting it for use in commercial products such as soap.

Goni warns that scientists' current understanding of sargassum growth may change as more is known about these accumulations.

"What we think we know today may change tomorrow," he says.