Record Sargassum Seaweed Blob Heading for Florida Beaches Already Swamped With Red Tide

Marine biologists are tracking a 5,000 mile-wide sargassum seaweed blob so large it’s visible from space, and it’s heading for Florida’s Gulf Coast. Sargassum blooms are nothing new, but scientists think this could be the largest one in history.

Scientists have found that climate change is causing ocean temperatures to rise, creating a more ideal environment for the algae to thrive. Meanwhile, urban and agriculture runoff is sending nitrates from fertilizers and other nutrients flowing into the ocean, feeding the bloom.

The blanket of seaweed spans twice the width of the continental U.S. and is already affecting some beaches in the Florida Keys. Parts of the Mayan Riviera were warned last week they could see three feet of sargassum buildup.

The thick mat of algae drifts between the Atlantic coast of Africa and the Gulf of Mexico, and provides habitat for marine life while absorbing carbon dioxide, but as it comes to shore it can block light from reaching coral reefs, and negatively impacts air and water quality as it decomposes.

The mess can trap boats and other machinery, block intake valves for power and desalination plants, and cause respiratory problems for humans as the rotting seaweed releases hydrogen sulfide.


The west coast of Florida is already grappling with an algae bloom called red tide, which results in massive amounts of dead fish washing ashore, as well as the deaths of marine mammals, sea turtles, sea birds.

There are also impacts for humans, including spring breakers. Florida’s Fish And Wildlife Conservation Commission warns people not to swim in or near red tide waters, which can cause skin irritation, rashes, burning and sore eyes.

The toxic red tide algae is known as Karenia brevis, and produces what are known as brevetoxins. The brevetoxins can also become airborne and cause coughing and congestion, especially affecting those with asthma or lung conditions.

Eating shellfish affected by the toxins can cause Neurotoxic Shellfish Poisoning leading to gastrointestinal issues, tingling of the mouth, and other symptoms.

NPR, Mote Lab & Aquarium

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