SARGASSUM BLOOMS AND MARINE PLASTIC BRING POTENTIALLY UNHEALTHY BACTERIA TO THE BEACH

Sargassum blooms and marine plastic bring potentially unhealthy bacteria to the beach. A huge mass of seaweed filled with plastic and bacteria could have unhealthy effects on the coasts of Florida and the Caribbean. This is what research in Linda Amaral-Zettler’s group recently published alongside colleagues in the United States. Some media have reported that among these bacteria might be a “flesh-eating” species known as Vibrio vulnificus, but that is not the case.

The brown alga, called Sargassum, is native to the Sargasso Sea in the North Atlantic Ocean. In recent years the algae have become a growing problem for beachgoers around the world as the algae wash ashore en masse.

Sargassum debris on the beach is, in addition to being smelly and immense, filled with bacteria of the genus Vibrio, according to the new research. “It is clear that Vibrio colonizes both plastic debris and Sargassum well. The Vibrio bacteria may also carry genes that are potentially pathogenic,” said Linda Amaral-Zettler, marine biologist at the Royal Netherlands Institute for Sea Research and senior corresponding author of the study.

The team identified several previously undescribed Vibrio species in water, plastic, and algal samples which carry key genes that their pathogenic relatives also have. “This means that these bacteria may also have the ‘machinery’ needed to infect humans and cause disease,” Amaral-Zettler said.

About a dozen species of bacteria in the genus Vibrio cause vibriosis, a disease that can occur when people ingest the bacteria or when the microbes infect an open wound. If eaten, the bacteria can cause severe diarrhoea, abdominal cramps, fever, and vomiting. As for wound infections, one species of Vibrio can sometimes cause so-called flesh-eating infections, scientifically known as necrotising fasciitis, in which the skin around the infected wound rapidly dies.

Risks of Sargassum and plastic on the beach 

“I don’t think anyone at this point has thought about these microbes and their ability to cause infections,” said Tracy Mincer, first author and scientist at Florida Atlantic University. “We want to make the public aware of these risks. We should be especially careful about harvesting and processing Sargassum biomass until the risks are more thoroughly investigated.”

And what does that mean for beachgoers? “I don’t think people need to panic about Sargassum, but they do need to be responsible and realise that there are dangers when you expose yourself to these kinds of materials,” Amaral-Zettler says. It is important to note that Sargassum seaweed masses can also contain a lot of plastic, to which Vibrio bacteria can quickly attach and multiply within minutes, the study found. There are also already known risks associated with Sargassum washing up on the beach, such as eye and throat irritation from toxins released by the rotting seaweed.

Risks to marine life 

The Vibrio on seaweed can have environmental consequences. For example, like humans, fish can get diarrhoea after ingesting the bacteria. That extra faeces provides extra nutrients in the water. This can lead to more Sargassum.  

Algal blooms can smother coral reefs. Also, the large amounts of algae cause a decrease in oxygen in the water as the algae die and rot. This causes a “dead zone” where other marine animals cannot survive.

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