Florida seaweed bloom: What is sargassum and why are people worried about it?

Sargassum in the Florida Keys

It's due to be a record year for sargassum, a fast-spreading seaweed bloom which can be seen from Space.

Sargassum with its golden branches looks pretty and in normal amounts can be a good thing, but when it is expanding at the rate it is, it an be quite damaging.

According to the Sargassum Monitoring Unit, levels are higher than ever and the seaweed is washing up on beaches in Florida in the US earlier than expected ahead of its usual high season in May and June.

But what is sargassum and why is it such a problem?

What is sargassum?

Sargassum is a type of seaweed. It is yellow/brown and is sometimes known as the "floating golden rainforest".

Although most seaweed has roots, sargassum has 'berries' or gas filled bubbles which allow it to float.

Floating rafts of sargassum can stretch for miles across the ocean.

It can provide food and a place to live for a wide range of sea creatures such as fish, turtles and shrimp.

The Sargasso sea, an area in the North Atlantic defined by its currents, is named for the huge amount of sargassum which provides a unique ecosystem for the many marine animals which live there.

Some animals like the Sargassum crab, the Sargassum slug and the Sargassum pipefish have specially adapted to live there.

Why is sargassum a problem in Florida and parts of the Caribbean?

Sargassum on the shore of Le Gosier on the French overseas islands of Guadalope

In May 2011 sargassum was found near Brazil, far South of the Sargasso sea. By September 2011 it had spread from there to the coast of Africa.

This huge band of sargassum kept growing and scientists were puzzled as to why.

In June 2018, scientists recorded 20 million metric tons of seaweed, a 1,000% increase compared with the 2011 bloom for that month.

More than 24 million tons of sargassum covered the Atlantic in June 2022, according to the University of South Florida's Optical Oceanography Lab, this beat the record, set in 2018, by 20%.

It had increased from 18.8 million tons in May 2022.

It now spans thousands of miles along the Caribbean coastline.

While they don't know exactly what caused it to suddenly appear in such great amounts, scientists suggested it could be due to increase of water temperatures as a result of climate change and nitrogen-heavy fertilisers and sewage waste.

How is sargassum damaging?

Mexico has spent millions of pounds on removing Sargassum from its beaches

A lot of the areas affected by sargassum are very popular with tourists.

When the seaweed washes onto the beaches, it forms huge piles which start to rot and smell.

It is difficult and expensive to get rid of. Mexico has spent approximately $17 million (£14 million) on removing seaweed from its Caribbean beaches.

In February this year one Mexican state issued a red alert when excessive levels appeared on 40 beaches.

The French island of Guadeloupe in the Caribbean issued a health alert in late July 2022.

The gas called hydrogen sulphide it releases when it rots has been shown by some studies to cause breathing problems for people with asthma.

And although in the Sargasso sea the seaweed is an environmental haven, such blankets of sargassum near the coast can smother coral beds and prevent coastal fish from getting oxygen.

Marine mammals and turtles can get tangled up in the stuff and studies have shown the sargassum washed onto shore can affect nesting turtles.

Is there a solution to sargassum?

Scientists say there could be positive uses for the washed-up sargassum

Some scientists say in order to stop sargassum spreading there needs to be less deforestation and more sewage treatment, this would limit the amount of fertiliser getting into the water which is helping it to grow.

Other scientists and experts have looked at how sargassum might be used in a positive way.

In Mexico, sargassum seaweed has been partially used to make building bricks for low-cost homes.

And a 2020 study by UK researchers worked out a process which would cheaply turn sargassum seaweed into biofuel.