Seaweed invades prestigious beaches in West Africa, Caribbean
July 17 2016 01:36 AM
A file photo of the River No. 2 Village Beach in Sierra Leone. Every summer for the last few years, there has been an influx of seaweed on beaches across Sierra Leone and other countries along the west coast of Africa. Photo by Annabel Symington

By Steff Gaulter

It might be too hot to use them at the moment, but the beaches in Qatar are beautiful. It’s nice to know they’ll still be there, ready to use, when the weather finally improves in the autumn. Not all countries are so lucky.
In many parts of West Africa and the Caribbean, vast amounts of seaweed is being found on some of the most prestigious beaches. The seaweed isn’t just ugly, it’s pungent and it’s coming ashore in such large quantities that it is in danger of ruining the tourism and the fishing industries.
Just in the past few weeks, Sierra Leone has again reported a huge magnitude of the seaweed has been washed up on its beaches. It’s a tragedy for the country which is famed for its white sands, beaches so beautiful that they were used as the backdrop for the 70s advert for the chocolate bar ‘Bounty’. Until the civil war in 1991, the sand used to host around 30,000 tourists a year. Now those numbers have dropped considerably, but the beaches remained pristine. However, that was before the influx of seaweed.
The amount of seaweed is so immense that some of the beaches are being cleared every day using dredgers, but it is still appearing in huge volumes. The stench is keeping tourists away and fishermen are complaining that they can’t even lower their nets, as they would simply fill with seaweed. This is having a disastrous effect on their livelihoods where many people live hand to mouth: if they don’t have fish to sell, they don’t have money or food to eat for their families.
This is not the first time that Sierra Leone has been inundated by the smelly seaweed. Every summer for the last few years, there has been an influx, and it has not only been confined to Sierra Leone. Nine countries along the west coast of Africa, spanning from Senegal to Nigeria, have also had their beaches clogged by the seaweed and the invasion has also affected the beaches across the other side of the Atlantic.
West Africa suffered its first influx in 2011, and at the same time parts of the Caribbean were also inundated, and more seaweed was also spotted off the coast of Brazil.
The type of seaweed that’s responsible for the inundation is sargassum, a brown substance which forms large floating mats. It’s an unusual type of seaweed because it reproduces on the surface of the ocean waves, rather than on the ocean floor like other seaweeds.
It usually lives in the Sargasso Sea, a three million square kilometre body of water in the north Atlantic to the east of the USA. The plant is so abundant in this region that the sea was named after it. It provides a critical habitat for many marine species such as mahi-mahi, tuna, eels and sea turtles. Not only does the seaweed provide food, but the vast mats also offer protection for huge numbers of juvenile fishes.
Until 2011, the mats of sargassum remained in the middle of the ocean. A small amount usually washed up along tropical shores, which wasn’t a problem. However, severe inundations can wipe out fish populations, harm tourism and cause coastal dead zones.
Seaweeds are a type of algae, so huge inundations are known as ‘harmful algae blooms’. 2011 is thought to be the first time that an inundation of such a great scale occurred that beaches from the Caribbean to West Africa were affected. Since then, however, the seaweed has been a recurring problem and 2015 saw a particularly intense inundation.
Scientists at the Gulf Coast Research Laboratory at the University of Southern Mississippi who are studying the inundations have used ocean currents to trace the seaweed back to its origins. They have demonstrated that the seaweed didn’t come from its usual habitat in the Sargasso Sea, instead it came from just south of the equator.
In 2010, the year before the first influx of seaweed, there were unusually high temperatures in the Atlantic.  It was also an unusual year for ocean currents, and scientists believe that some sargassum found itself stuck in a circulation just south of the equator. This seaweed was fed by rich nutrients from the outflows of the Amazon and Congo rivers, as well as dust which drifted in from Chad. The dust contains useful minerals such as nitrogen, phosphorus and iron. It is believed that the combination of warm water and nutrients allowed the sargassum to thrive in its new environment.
In summer months, this ocean circulation normally breaks down. In 2010, however, it didn’t and the sargassum was able to grow undisturbed for a whole year. In 2011 when the current finally did weaken, the sargassum escaped and floated silently to the beaches on either side of the Atlantic. Now that the seaweed is growing in this part of the ocean, it is impossible to say whether these inundations will eventually fade away, or whether they are now a permanent feature of the environment in West Africa and the Caribbean.
More research needs to be done, but tourism and fishing could seriously suffer if the vast quantities of seaweed continue to wash up onto the shore.

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