The Impact of Sargassum Seaweed and Plastic on Beaches: Risks to Health and Marine Life

A huge pile of seaweed, full of plastic and bacteria, could have unhealthy effects on the coasts of Florida and the Caribbean. This is what Linda Amaral-Zettler recently published an article about, together with colleagues from the United States. Some media outlets have reported that these bacteria may include a “flesh-eating” species known as Vibrio vulnificus, but that is not the case.

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

Sargassum remains on the beach are next to smelly and heavy, according to the new research, filled with bacteria from the genus Vibrio. “It is clear that Vibrio colonizes both plastic waste 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 (NIOZ) and final author of the research.

The team identified a number of previously undescribed Vibrio species in water, plastic and algae samples that carry key genes shared by their pathogenic peers. “This means that these bacteria may also have the ‘machinery’ needed to infect humans and cause disease,” said Amaral-Zettler.

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

“I don’t think anyone has thought about these microbes and their ability to cause infection at this point,” said Tracy Mincer, first author at Florida Atlantic University. “We want to raise public awareness of these risks. We need to 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 should run screaming from Sargassum. But they should be responsible and realize that there are dangers in exposing yourself to these kinds of materials,” says Amaral-Zettler. It’s important to note that the Sargassum seaweed clumps are also high in plastic, which Vibrio bacteria can quickly attach to and multiply within minutes, the study found. In addition, there are also known risks associated with the Sargassum washing up on the beach, such as irritation of the eyes and throat due to toxic substances released from the decaying seaweed.

The Vibrio on seaweed can have consequences for the environment. For example, just like humans, fish can develop diarrhea after ingesting Vibrio bacteria. That extra stool provides extra nutrients in the water. This can lead to more Sargassum.

The algae infestations can choke coral reefs. In addition, the large amounts of algae cause a decrease in the oxygen in the water when the algae die and start to rot. This creates a “dead zone” in which other sea creatures cannot survive.