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New threat in seaweed blooms a concern for Florida's beaches

  • New threat in seaweed blooms concern for Florida's beaches
    Credit: Volusia Beaches Twitter account
  • Sargassum seaweed blooms can become a nuisance when large amounts wash up on shore, affecting tourism and wildlife.
  • Current removal challenges in the beaches of Florida have compounded as scientists have discovered that Sargassum may contain Vibrio bacteria, which can pose a risk to human health.

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Seaweed has been gaining attention for its benefits in various industries; one type of brown seaweed, Sargassum, provides important ecosystem services, but huge blooms of it may become a nuisance when large amounts arrive on shore. Large masses of Sargassum have been washing up on the beaches of Florida, and may carry with them an additional threat in the form of bacteria found in the decomposing algae, reports The Guardian.

The Great Atlantic Sargassum Belt is a mass of floating seaweed that stretches for 5,000 miles. While this seaweed is a natural part of the ocean food chain, massive blooms of Sargassum, fuelled by nutrient pollution from land sources, have been a problem for more than a decade, impacting tourism and wildlife. Rotting seaweed piles up on beaches and removal can be very costly.

The latest threat posed by Sargassum was discovered by scientists at Florida Atlantic University who found the Great Atlantic Sargassum Belt contains high levels of Vibrio bacteria, which could pose a risk for human health. They studied the pathogenic potential of bacteria colonising seaweed and plastic marine debris (PMD) in the Sargasso Sea – the first place where PMD was described in the 70s – and concluded that species of Vibrio in the open ocean warrant risk assessment as emerging pathogens, and “caution should also be exercised regarding the harvest and processing of Sargassum biomass until the risks are explored more thoroughly”.

Vibrio bacteria naturally live in the ocean, and a number of species cause an illness known as vibriosis in humans, according to the CDC. People can become infected consuming raw or undercooked seafood such as oysters. However, one species, Vibrio vulnificus, can cause a skin infection through an open wound; life-threatening wound infections can kill about 1 in 5 people, as some lead to necrotizing fasciitis, also known as “flesh-eating disease”.

The new threat has become a concern for clean-up crews and tourists, who are instructed to avoid direct contact with the seaweed. “It’s very alarming in the first place to see it on the beaches, and alarming to see all the plastic that is entangled in it. And now even more than that, there’s harmful bacteria too. That’s so scary,” said Sophie Ringel, from the non-profit Clean Miami Beach.

The Florida Department of Health advises people to avoid Sargassum, especially individuals with weakened immune systems. Meanwhile, the state's Department of Environmental Protection is working with the Florida fish and Wildlife Conservation Commission and local governments to monitor the seaweed belt and has allocated funds for clean-up efforts. Maintenance crews remove Sargassum with heavy machinery from the shoreline on Miami Beach and Key Biscayne, early most mornings, after surveyors check for turtle nests.

The good news, at least momentarily, is scientists have observed a 15% decrease in the amount of Sargassum in the Atlantic in May using satellite imaging. However, the amount of this seaweed has been increasing in recent years and is expected to continue to do so. A stark reminder of the impact we have on oceans and our duty to protect the ocean environment to prevent risks for ecosystems, public health and livelihoods, as we celebrate World Oceans Day today.

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